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Introduction The rectifier diode is a semiconductor device that converts AC into DC. Usually it contains a PN junction with two terminals, a positive electrode and a negative electrode. The most important characteristic is unidirectional conductivity. In electronic circuits, its breakdown voltage is high, the reverse leakage current is small, and the high temperature performance is good. Generally, it can be made of materials such as semiconductor germanium or silicon. In addition, high-voltage and high-power rectifier diodes are made of high-purity single crystal silicon (it is easy to reverse breakdown when there is more doping). This kind of device has a large junction area and can pass a large current (up to thousands of amperes), but the operating frequency is not high, generally below tens of KHz. Rectifier diodes are mainly used in various low-frequency half-wave rectifier circuits. If require full-wave rectification, several diodes need to be connected to form a rectifier bridge. What is a Rectifier? (AC to DC) Catalog Introduction Ⅰ Common Parameters Ⅱ Rectifier Diodes Selection Ⅲ Rectifier Common Failures Ⅳ Rectifier Diodes Detection Ⅴ Rectifier Diode Replacement 5.1 Replacing Rules 5.2 Commonly Used Rectifier Models List Ⅵ Rectifier Diode Circuit Types 6.1 Half-Wave Rectifier Circuit 6.2 Full-Wave Rectifier Circuit 6.3 Bridge Rectifier Circuit Ⅶ High-frequency Rectifier Diodes Ⅷ FAQ Ⅰ Common Parameters The rectifier diode uses the unidirectional conductivity of the PN junction to convert alternating current into pulsating direct current. Rectifier diodes have a large leakage current, and most of them are diodes packaged with surface mount materials. The parameters of the rectifier diode include the maximum rectifier current, which refers to the maximum current value allowed by the rectifier diode for long-term operation. It is the main parameter of the rectifier diode and the main basis for the option of the rectifier diode. Except it, other important parameters are introduced here.(1) Maximum average rectified current IF: It refers to the maximum forward average current allowed to pass through the diode during long-term operation. The current is determined by the PN junction area and the heat dissipation conditions. It should be noted that the average current passing through the diode cannot be greater than this value, and has heat dissipation.(2) Maximum reverse working voltage VR: It refers to the maximum reverse voltage allowed to be applied across the diode. If it is greater than this value, the reverse current (IR) will increase sharply, and the unidirectional conductivity of the diode will be destroyed, causing reverse breakdown. Usually take half of the reverse breakdown voltage VB as VR.(3) Maximum reverse current IR: It is the reverse current allowed to flow through the diode under the highest reverse working voltage. This parameter reflects the quality of the unidirectional conductivity of the diode. Therefore, the smaller the current value, the better the diode quality.(4) Breakdown voltage VB: It refers to the voltage value at the sharp bend point of the reverse volt-ampere characteristic curve of the diode. When the reverse is a soft characteristic, it refers to the voltage value under a given reverse leakage current condition.(5) The highest operating frequency fm: It is the highest operating frequency of the diode under normal conditions. It is mainly determined by the junction capacitance and diffusion capacitance of the PN junction. If the operating frequency exceeds fm, the unidirectional conductivity of the diode will not be well reflected.(6) Reverse recovery time trr: It refers to the reverse recovery time under the specified load, forward current and maximum reverse transient voltage.(7) Zero-bias capacitor CO: It refers to the sum of the capacitance of the diffusion capacitance and the junction capacitance when the voltage across the diode is zero. It is worth noting that, due to the limitation of the manufacturing process, even the same type of diode has a large dispersion of its parameters. The parameters given in the manual are often within a range. If the test conditions change, the corresponding parameters will also change. For example, the IR of the 1N5200 series silicon plastic rectifier diode measured at 25°C is less than 10uA, and at 100°C IR becomes less than 500uA.     Ⅱ Rectifier Diodes Selection Rectifier diodes are generally planar silicon diodes, which are used in various power rectifier circuits. When selecting a rectifier diode, the parameters such as its maximum rectifier current, maximum reverse working current, cut-off frequency and reverse recovery time should be mainly considered.The rectifier diode used in the ordinary series stabilized power supply circuit does not require high reverse recovery time of the cut-off frequency. The rectifier diode with the maximum rectified current and maximum reverse working current should meet the requirements of the circuit.The rectifier diode used in the rectifier circuit of the switching regulated power supply and the pulse rectifier circuit should be a rectifier diode with a higher operating frequency and shorter reverse recovery time (such as RU series, EU series, V series, 1SR series, etc.) or select fast recovery diodes, or Schottky rectifier diode.     Ⅲ Rectifier Common Failures (1) Inadequate lightning protection and poor overvoltage protection. The rectifier device is not equipped with lightning protection and overvoltage protection devices. Or insufficient routine maintenance of the equipment.(2) Poor operating conditions. In the indirect drive generator set, because the calculation of the speed ratio is incorrect or the ratio of the diameters of the two belt pulleys does not meet the requirements of the speed ratio, the generator runs at a high speed for a long time, so the rectifier is at a higher voltage for a long time. It accelerates the rectifier aging, and was damaged by premature breakdown.(3) Poor operation management. The load failure or diode breakdown doesn’t fixed in time.(4) Poor equipment installation or manufacturing process. The generator set has been operating under large vibration for a long time, which affects the rectifier tube operation. At the same time, because the generator set speed is unstable, the working voltage of the rectifier tube also fluctuates, which greatly accelerate the aging and damage of the rectifier tube.(5) The specifications and models of the rectifier tube do not match. When replacing a new rectifier tube, wrongly replace the tube whose working parameters do not meet the requirements or the wiring is wrong, causing the rectifier tube to breakdown and damage.(6) The safety margin of the rectifier tube is too small. The overvoltage and overcurrent safety margin of the rectifier tube is too small, so that the rectifier tube cannot withstand the overvoltage or the peak value of the overcurrent transient process that occurs in the generator excitation circuit and is damaged. Figure 1. Diode as Rectifier Symbol     Ⅳ Rectifier Diodes Detection Here is a more general and simple method. Remove all the rectifier diodes in circuit, use the 100×R or 1000×R ohm range of a multimeter to measure the two lead wires of the rectifier diode (adjust and test twice). If the resistance values measured twice are very different, for example, the resistance value is as high as a few hundred kΩ to infinity, or the resistance value is only a few hundred Ω or less, indicating that the diode is good (except under special circumstances). If the resistance value measured twice is almost the same and the resistance value is very small, it means that the diode has been broken down and cannot be used. In addition, if the resistance values measured twice are both infinite, it means that the diode has been internally disconnected and cannot be used.     Ⅴ Rectifier Diode Replacement   5.1 Replacing Rules After the rectifier diode is damaged, you should replace with the same model or another model with the same parameters.Generally, rectifier diodes with high withstand voltage (reverse voltage) can be substituted for rectifier diodes with low withstand voltage, while rectifier diodes with low withstand voltage cannot be replaced with rectifier diodes with high withstand voltage. A diode with a high rectification current value can be substituted for a diode with a low rectification current value, while a diode with a low rectification current value cannot be substituted for a diode with a high rectification current value.   5.2 Commonly Used Rectifier Models List Material Model Reverse Voltage Operation (peak) Average Rectified Current   Silicon Rectifier Diode 1N4001 50V 1A (Ir=5uA,Vf=1V,Ifs=50A) 1N4002 100V 1A 1N4003 200V 1A 1N4004 400V 1A 1N4005 600V 1A 1N4006 800V 1A 1N4007 1000V 1A 1N4148 75V 4PF, Ir=25nA,Vf=1V 1N5391 50V 1.5A (Ir=10uA,Vf=1.4V,Ifs=50A) 1N5392 100V 1.5A 1N5393 200V 1.5A 1N5394 300V 1.5A 1N5395 400V 1.5A 1N5396 500V 1.5A 1N5397 600V 1.5A 1N5398 800V 1.5A 1N5399 1000V 1.5A 1N5400 50V 3A (Ir=5uA,Vf=1V,Ifs=150A) 1N5401 100V 3A 1N5402 200V 3A 1N5403 300V 3A 1N5404 400V 3A 1N5405 500V 3A 1N5406 600V 3A 1N5407 800V 1A (Ir=5uA,Vf=1V,Ifs=50A) 1N5408 1000V 1A   Ⅵ Rectifier Diode Circuit Types The power grid supplies users with alternating current, and various electrical devices require direct current. Rectification is the process of converting AC into DC. Utilizing the device with unidirectional conductivity, the current of alternating direction and magnitude can be converted into direct current. The following introduces three main rectifier circuits composed of crystal diodes.   6.1 Half-Wave Rectifier Circuit Figure 2. Half-Wave Rectifier Circuit The figure shows the simplest rectifier circuit. It is composed of power transformer B, rectifier diode D and load resistor Rfz. The transformer transforms the voltage into the required alternating voltage e2, and then D transforms the AC into pulsating DC.The transformer threshold voltage e2 is a sine wave voltage whose direction and magnitude change with time, and its waveform is shown in Figure (a). In the 0~K time, e2 is a positive half cycle, that is, the upper end of the transformer is positive and the lower end is negative. At this time, the diode is in forward conductive conduction, and e2 is added to the load resistor Rfz through it. Within π~2π, e2 is in negative half cycle, the lower end of the transformer secondary is positive, and the upper end is negative. At this time, D bears the reverse voltage and does not conduct, and there is no voltage on Rfz. In the time of π~2π, the process of 0~π time is repeated, and in the time of 3π~4π, the process of π~2π time... half-cycle through Rfz, a single right direction voltage is obtained on Rfz (up positive and lower negative), as shown in Figure (b), which achieves the purpose of rectification. But the load voltage Usc, and the load current also changes with time, so it is usually called pulsating DC. Figure 3. Half-Wave Rectifier Wave This rectification method of removing the first half week and leaving half a week is called half wave rectification. It is not difficult to note that the half-wave rectification is at the expense of consuming half of the AC in circuit, and the current utilization rate is very low. According to it, half-wave rectifier diode is commonly used in high voltage and small current occasions, and is rarely used in general radio devices.   6.2 Full-Wave Rectifier Circuit Figure 4. Full-Wave Rectifier Circuit If some adjustments are made to the structure of the rectifier circuit, a full-wave rectifier circuit that can be obtained. The figure above is the electrical schematic diagram of the full-wave rectifier circuit.The full-wave rectifier circuit can be regarded as a combination of two half-wave rectifier circuits. A tap needs to be drawn in the middle of the secondary coil of the transformer to divide the secondary coil into two symmetrical windings, so as to get two voltages e2a and e2b of equal size but opposite polarity to form two energized circuits.The working principle of the full-wave rectifier circuit can be illustrated by the waveform diagram. Between 0 and π, e2a is a positive voltage to Dl, D1 is turned on, and a up positive and down negative voltage is obtained on Rfz. e2b is a reverse voltage to D2, and D2 is not conductive (see Figure(b) ). In the time of π-2π, e2b is a positive voltage to D2, D2 is turned on, and the voltage obtained on Rfz is still up positive and down negative voltage, therefore e2a is a reverse voltage to D1, and D1 is not conductive (see figure (c). Figure 5. Full-Wave Rectifier Circuit Wave Repeated this way, because the two rectifier elements D1 and D2 conduct electricity in turn, the result is that the load resistor Rfz has the same direction of current at the positive and negative half cycles, as shown in Figure(b). This is full-wave rectification, which not only uses the positive half-cycle, but also cleverly uses the negative half-cycle. Full-wave rectifier greatly improves the rectification efficiency. Figure 6. Full-Wave Rectifier Circuits This circuit requires the transformer to have a secondary center tap that makes the two ends symmetrical, which brings a lot of trouble to the production. In addition, in this circuit, the maximum reverse voltage that each rectifier diode can withstand is twice the maximum value of the transformer secondary voltage, so diodes should withstand higher voltages.   6.3 Bridge Rectifier Circuit Figure 7. Bridge Rectifier Circuit The bridge rectifier circuit is the most used rectification circuit. It has the advantages of a full-wave rectifier circuit as long as two diode ports are connected to form a bridge structure, so its shortcomings are overcome to a certain extent.The bridge rectifier circuit is as follows: Figure 8. Bridge Rectifier Circuit (a) When e2 is a positive half cycle, D1, D3 and the direction voltage, D1, D3 are turned on; D2, D4 are applied with reverse voltage, they are turned off. E2, Dl, Rfz, and D3 are energized a loop in the circuit. On Rfz, a positive and negative half-wave washing voltage is formed. When e2 is a negative half cycle, a positive voltage is applied to D2 and D4, and they are turned on; Apply reverse voltage to D1 and D3, they are cut off. E2, D2Rfz, and D4 are energized a loop in the circuit, and the other half-wave rectified voltage is also formed on Rfz. Figure 9. Bridge Rectifier Circuit (b) If repeated, a full-wave rectified voltage at Rfz is made. The waveform diagram is the same as the full-wave rectifier. It is not difficult to see from the figure that the reverse voltage of each diode in the bridge circuit is equal to the maximum value of the secondary voltage of the transformer, which is half smaller than the full-wave cleaning circuit.     Ⅶ High-frequency Rectifier Diodes The rectifier diode in the switching power supply must have the characteristics of low forward voltage reduction and fast recovery, and should also have sufficient output power. The following three types of high-frequency diodes can be used: fast recovery rectifier, ultra-fast recovery rectifier, and Schottky diode rectifier.Fast recovery and ultra-fast recovery rectifier diodes have moderate and high forward voltage drop, and the range is from 0.8 to 1.2V. These two types of rectifier diodes also have higher cut-off voltage parameters. Therefore, they are particularly suitable for use in low-power auxiliary power circuits with output voltages around 12V.Compared with general rectifier diodes, the reverse recovery time difference between fast recovery rectifier diodes and ultra-fast recovery rectifier diodes is reduced to the nanosecond level, thus greatly improving the efficiency of the power supply. According to experience, when choosing a fast recovery rectifier diode, its reverse recovery time should be at least 1/3 of the rise time of the switching transistor. These two kinds of rectifier diodes also reduce the switching voltage spike, because it will affect the ripple of the output DC voltage.Whether fast recovery rectifier diodes and ultra-fast recovery rectifier diodes used in switching power supplies need a heat sink, which depends on the maximum power of the circuit. Under normal circumstances, the allowable junction temperature is 175°C during manufacture. The manufacturer has a technical parameters provided for the designer to calculate the maximum output operating current, voltage, and case temperature. Even under the action of a large forward current, the forward voltage drop of Schottky rectifier diodes is very low, only about 0.4V. Moreover, as the junction temperature increases, its forward voltage drop decreases. Therefore, Schottky rectifier diodes are particularly suitable for low-voltage output circuits around 5V. Its reverse recovery time is negligible, because this device is a semiconductor device with majority carrier. During the switching process of the device, there is no need to remove the stored charge of the minority carrier.Schottky rectifier diodes have two major shortcomings: First, the reverse cut-off voltage tolerance is low, about 100V; second, the reverse leakage current is large, making the device more susceptible to have heat breakdown than other types of rectifier devices. Of course, these shortcomings can also be overcome by adding a transient overvoltage protection circuit and appropriately controlling the junction temperature.     Ⅷ FAQ 1. How does a rectifier diode work?A rectifier is a device that converts an Alternating Current (AC) into a Direct Current (DC) by using one or more contact diodes. ... In simple words, a diode allows current in just one direction. This unique property of the diode allows it to act sort of a rectifier by converting an alternating current to a DC source.   2. What is a function of rectifier diode?A rectifier diode is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC).   3. What is the function of diode in rectifier circuit?A characteristic of diodes is that current flows (forward direction) or current does not flow (reverse direction) depending on the direction of applied voltage. This works to convert alternating current (AC) voltage to direct current (DC).   4. Which is used as rectifier?We know that the core use of rectifier is to convert AC current into DC current. The rectifier consists of semiconductor diodes to do this function.   5. What is the limitation of a diode rectifier?Disadvantages of Full Wave Bridge RectifierIt needs four diodes. The circuit is not suitable when a small voltage is required to be rectified. It is because, in this case, the two diodes are connected in series and offer double voltage drop due to their internal resistance.   6. What is the ideal rectifier diode efficiency?It is the ratio of DC output power to the AC input power. The rectifier efficiency of a full-wave rectifier is 81.2%.   7. What is a fast recovery rectifier?Definition: Fast Recovery Diode is a semiconductor device which possesses short reverse recovery time for rectification purpose at high frequency. A quick recovery time is crucial for rectification of high-frequency AC signal. Diodes are mostly used in rectifiers because they possess ultra-high switching speed.   8. Which diode is fast recovery diode?FRD stands for fast recovery diodes. They offer high-speed support and generally have a trr of approximately 50 to 100 ns. With a VF of approximately 1.5V, it is rather large when compared to general rectifying diodes. Another generic term for the FRD type would be a “High-speed Diode.”   9. What is ultra fast recovery diode?A fast diode is a faster-than-standard current rectifier. ... A fast rectifier typically recovers ten times faster than a standard rectifier, and an ultrafast designation is usually applied to rectifiers designed to beat the standard rectifier recovery by being more than fifty times faster.   10. What is the difference between a Schottky diode and a rectifier diode?Schottky diode, also known as barrier diode is mainly used in low voltage circuits because the forward voltage drop of Schottky diode(Vf) is less than a rectifier diode. The forward voltage drop of a Schottky diode is typically in the range of . 25 to 0.5 V whereas the Vf of a rectifier diode is around 0.7 volts.   11. What is Schottky barrier rectifier?The Schottky diode or Schottky Barrier Rectifier is named after the German physicist Walter H. Schottky, is a semiconductor diode designed with a metal by the semiconductor junction. It has a low-forward voltage drop and a very rapid switching act. ... Actually, it is one of the oldest semiconductor devices in reality.

IntroductionThe manufacture of each semiconductor components products requires hundreds of processes. After sorting, the entire manufacturing process is divided into eight steps: Wafer Processing, Oxidation, Photography, Etching, Film Deposition, Interconnection, Test, and Package.Figure 1. Semiconductor Parts Manufacturing ProcessCatalogIntroductionⅠ Wafer ProcessingⅡ OxidationⅢ PhotomaskⅣ EtchingⅤ Film DepositionⅥ InterconnectionⅦ TestⅧ PackageⅠ Wafer ProcessingFewer people know, all semiconductor processes start with a grain of sand. Because the silicon contained in sand is the raw material needed to produce wafers. A wafer is a round slice formed by cutting a single crystal column made of silicon (Si) or gallium arsenide (GaAs). To extract high-purity silicon materials, silica sand is required, a special material with a silicon dioxide content of up to 95%, which is also the main raw material for making wafers. Wafer processing is the process of making and obtaining wafers.Semiconductor Production Process Explained① Ingot CastingFirst, the sand needs to be heated to separate the carbon monoxide and silicon, and the process is repeated until the ultra-high purity electronic grade silicon (EG-Si) is obtained. High-purity silicon melts into a liquid, and then solidifies into a single-crystal solid form called an "ingot", which is the first step in semiconductor manufacturing. The manufacturing precision of silicon ingots (silicon pillars) is very high, reaching the nano level.② Ingot CuttingAfter the previous step is completed, you need to cut off both ends of the ingot with a diamond saw, and then cut it into slices of a certain thickness. The diameter of the ingot slice determines the size of the wafer. Larger and thinner wafers can be divided into more units, which helps reduce production costs. After cutting the silicon ingot, it is necessary to add a "flat area" or "indent" mark on the slice, so that it is convenient to set the processing direction based on it as a standard in the subsequent steps.③ Wafer Surface PolishingThe thin slice obtained through the above-mentioned cutting process is called a "die", that is, an unprocessed "raw wafer". The die surface is uneven, and it is impossible to directly print circuit patterns on it. Therefore, it is necessary to first remove surface defects through grinding and chemical etching processes, then form a smooth surface through polishing and then cleaning residual contaminants. Ⅱ OxidationThe role of the oxidation process is to form a protective film on the surface of the wafer. It can protect the wafer from chemical impurities, prevent leakage current from entering the circuit, diffusion during ion implantation, and the wafer from slipping off during etching.Figure 2. OxidationThe first step of the oxidation process is to remove impurities and pollutants, such as organic matter, metals and evaporation residual moisture with four steps. After the cleaning is completed, the wafer can be placed in a high temperature environment of 800 to 1200 degrees Celsius, and a layer of silicon dioxide is formed by the flow of oxygen or vapor on the wafer surface. Oxygen diffuses through the oxide layer and reacts with silicon to form oxide layers of different thicknesses, which can be measured after the oxidation is complete.✔️Dry Oxidation and Wet Oxidation MethodAccording to the different oxidants in the oxidation reaction, the thermal oxidation process can be divided into dry oxidation and wet oxidation. The former uses pure oxygen to produce a silicon dioxide layer, which is slow but the oxide layer is thin and dense. The latter requires both oxygen and high solubility. The characteristic of water vapor is that the growth rate is fast, but the protective layer is relatively thick and the density is low.Figure 3. Dry Oxidation and Wet Oxidation MethodIn addition to the oxidizer, there are other variables that affect the thickness of the silicon dioxide layer. First of all, the wafer structure, surface defects and internal doping concentration will affect the rate of formation of the oxide layer. In addition, the higher the pressure and temperature generated by the oxidation equipment, the faster the oxide layer will be formed. In the oxidation process, it is also necessary to use dummy wafers according to the location of the wafers in the unit to protect the wafers and reduce the difference in oxidation degree. Ⅲ PhotomaskPhotomask is the use of light to "print" circuit patterns onto a wafer. We can understand it as semiconductor parts drawing on the surface of the wafer. The higher the fineness of the circuit pattern, the higher the integration of the product chip, which can only be achieved through advanced photomask technology. Specifically, it can be divided into three steps: photoresist coating, exposure and development.① Coated PhotoresistThe first step in drawing a circuit on a wafer is to coat photoresist on the oxide layer. Photoresist changes the chemical properties of the wafer to become "photographic paper". The thinner the photoresist layer on the surface of the wafer, the more uniform the coating, and the finer the patterns that can be printed. In addition, this step can use the "spin coating" method.Figure 4. Coating PhotoresistAccording to the difference of UV light reactivity, photoresist can be divided into two types: positive glue and negative glue. The former will decompose and disappear after being exposed to light, leaving a pattern of unreceived areas, while the latter will polymerize after being exposed to light to let the pattern of the light-receiving part appear.② ExposeAfter covering the photoresist film on the wafer, the circuit can be printed by controlling the light irradiation. This process is called "exposure." We can selectively pass light through the exposure equipment. When the light passes through the mask containing the circuit pattern, the circuit can be printed on the wafer coated with a photoresist film underneath.Figure 5. ExposureDuring the exposure process, the finer the printed pattern, the more components can be accommodated in the final chip, which helps to improve production efficiency and reduce the cost of individual components. ③ DevelopmentThe step after exposure is to spray developer on the wafer, in order to remove the photoresist in the area not covered by the pattern, so that the printed circuit pattern can be revealed. After the development is completed, it needs to be checked by various measuring equipment and optical microscopes to ensure the quality of the drawing of the circuit diagram. Ⅳ EtchingAfter the photolithography of the circuit diagram is completed on the wafer, an etching process is used to remove any excess oxide film and only the semiconductor circuit diagram is left. To do this, liquid, gas or plasma is used to remove the unselected parts.There are two main etching methods, depending on the material used: wet etching that uses a specific chemical solution for chemical reaction to remove the oxide film, and dry etching that uses gas or plasma.1) Wet EtchingFigure 6. Wet Etching MethodWet etching that uses chemical solutions to remove oxide films has the advantages of low cost, fast etching speed, and high productivity. However, wet etching has the characteristics of isotropy, that is, its speed is the same in any direction. This will cause the mask (or sensitive film) and the etched oxide film to not be completely aligned, making it difficult to process very fine circuit diagrams.2) Dry EtchingDry etching can be divided into three different types:The first is chemical etching, which uses etching gas (mainly hydrogen fluoride). Like wet etching, this method is also isotropic, which means that it is not suitable for fine etching.The second method is physical sputtering, that is, ions in the plasma are used to strike and remove the excess oxide layer. As an anisotropic etching method, it has different etching speeds in the horizontal and vertical directions, so its fineness must exceed that of chemical etching. However, the disadvantage of this method is that the etching speed is slow, because it completely relies on the physical reaction caused by ion collision.Figure 7. Physical SputteringThe third method is reactive ion etching (RIE). It combines the first two methods, that is, while using plasma for ionized physical etching, and chemical etching is performed with free radicals generated after plasma activation. In addition to the etching speed exceeding the first two methods, RIE can use the characteristics of ion anisotropy to achieve high-definition pattern etching.Figure 8. Reactive Ion Etching (RIE)Now dry etching has been widely used to improve the yield of fine semiconductor circuits. Maintaining the uniformity of full-wafer etching and increasing the etching speed are crucial. Today's most advanced dry etching equipment is supporting the production of the most advanced logic and memory chips with higher performance. Ⅴ Film DepositionIn order to create the micro devices inside the chip, we need to continuously deposit layers of thin films and remove the excess parts by etching, and add some materials to separate the different devices. Each transistor or memory cell is constructed step by step through the above process. The "thin film" we are talking about here refers to a "membrane" whose thickness is less than 1 micron (μm, one millionth of a meter) and cannot be manufactured by ordinary mechanical processing methods. Here the process of putting a thin film containing the desired molecular or atomic unit on the wafer is "deposition."Figure 9. DepositionTo form a multi-layer semiconductor structure, we need to fabricate a device stack first, that is, alternately stacking multiple thin metal (conductive) films and dielectric (insulating) films on the surface of the wafer, and then repeat the etching process to remove excess parts and form a three-dimensional structure. Technologies that can be used in the deposition process include chemical vapor deposition (CVD), atomic layer deposition (ALD) and physical vapor deposition (PVD). The methods using these technologies can be divided into dry and wet deposition.① Chemical Vapor DepositionFigure 10. Chemical Vapor DepositionIn chemical vapor deposition, the precursor gas chemically reacts in the reaction chamber and generates a thin film attached to the surface of the wafer and by-products that are drawn out of the chamber.Plasma-enhanced chemical vapor deposition requires the use of plasma to generate reactive gas. This method reduces the reaction temperature and is very suitable for temperature-sensitive structures. In addition, the use of plasma can also reduce the number of depositions, which can often lead to higher quality films.② Atomic Layer DepositionFigure 11. Atomic Layer DepositionAtomic layer deposition forms a thin film by depositing only a few atomic layers at a time. The key to this method is to loop the independent steps in a certain order and maintain good control. Coating the precursor on the wafer surface is the first step, after which different gases are introduced to react with the precursor to form the required substances on the wafer surface.③ Physical Vapor DepositionFigure 12. Physical Vapor DepositionPhysical vapor deposition refers to the formation of thin films by physical means. Sputtering is a physical vapor deposition method. Its principle is that atoms of the target material are sputtered out by the bombardment of argon plasma and deposited on the wafer surface to form a thin film.In some cases, the deposited film can be treated and improved by techniques such as ultraviolet heat treatment. Ⅵ InterconnectionThe conductivity of semiconductors is between conductors and non-conductors (ie insulators). This characteristic allows us to fully control the current. Through wafer-based lithography, etching and deposition processes, transistors and other components can be constructed, but they also need to be connected to achieve power and signal transmission and reception.Metal is used for circuit interconnection because of its conductivity, which is need to meet the following conditions:✔️Low Resistance: Since the metal circuit needs to pass current, the metal in it should have low resistance.✔️Thermochemical stability: The properties of the metal material must remain unchanged during the metal interconnection process.✔️High Reliability: With the development of integrated circuit technology, even a small amount of metal interconnect materials must have sufficient durability.✔️Manufacturing Cost: Even if the previous three conditions have been met, high cost is not suitable for the mass production.The interconnection process mainly uses two substances, aluminum (Al) and copper (Co).Figure 13. Al and Co Interconnection Process✔️Aluminum Interconnect ProcessThis process starts with aluminum deposition, photoresist application, and exposure and development, removing any excess aluminum and photoresist before entering the oxidation process through etching tech. After the foregoing steps are completed, repeat them until the interconnection is completed.With its excellent electrical conductivity, aluminum is also easy to lithography, etch, and deposit. In addition, it has a lower cost and a better adhesion to the oxide film. The disadvantage is that it is easy to corrode and has a low melting point. In addition, in order to prevent the reaction of aluminum and silicon from causing connection problems, it is also necessary to add a metal deposit to separate the aluminum from the wafer, which is called a "barrier metal."Aluminum circuits are formed by deposition. After the wafer enters the vacuum state, the thin film formed by aluminum particles will adhere to the wafer. This process is called "Vapour Deposition" and includes chemical vapor deposition and physical vapor deposition.✔️Copper Interconnection ProcessWith the improvement of semiconductor process precision and the shrinking of device size, the connection speed and electrical characteristics of aluminum circuits are gradually unable to meet the requirements. For this reason, we need to find new conductors that satisfy the requirements of both size and cost. With its lower resistance, so it can achieve faster connection speed. What’s more, copper is more reliable because it is more resistant to electromigration than aluminum, which is the movement of metal ions that occurs when current flows through the metal.However, copper does not easily form compounds, so it is difficult to vaporize and remove it from the wafer surface. To solve this problem, we no longer etch copper, but the dielectric materials, so that metal circuit patterns composed of trenches and via holes can be formed, and then copper is filled into the aforementioned to help interconnection, which is called "inlaid process".Figure 14. Copper Interconnection BarriersAs the copper atoms continue to diffuse into the dielectric, the insulation of the latter will decrease and produce a barrier layer that prevents the copper atoms from continuing to diffuse. Then a very thin copper seed layer will be formed on the barrier layer. After this step, electroplating can be carried out, that is, the high-aspect-ratio graphics are filled with copper. After filling, the excess copper can be removed by a metal chemical mechanical polishing (CMP) method. After completion, an oxide film can be deposited, and the excess film can be removed by photolithography and etching processes. The full entire process needs to be repeated continuously until the copper interconnection is completed.It can be seen from the above comparison that the difference between the copper interconnection and the aluminum interconnection is that the excess copper is removed by metal CMP instead of etching. Ⅶ TestThe main goal of the test is to check whether the quality of the semiconductor chip meets a certain standard, thereby eliminating defective products and improving the reliability of the chip. In addition, products that are tested and defective will not enter the packaging step, which helps to save cost and time. Electronic die sorting (EDS) is a testing method for wafers.EDS is a process for inspecting the electrical characteristics of each chip in the wafer state and thereby improving the semiconductor yield. EDS can be divided into five steps, as follows:Electrical Die Sorting (EDS)1）EPMTest whether the electrical parameters of transistors, capacitors, diodes and other devices meet the standards.2）Aging TestTest method of applying a certain temperature and AC/DC voltage to the wafer.3）TestPerform temperature, speed and motion tests on the wafer through the probe card.4）RepairReplace the components in the defective wafer and test again.5）InkUse special ink to mark defective chips.1) EPMEPM is the first step in semiconductor chip testing. This step will test every device (including transistors, capacitors, and diodes) that the semiconductor integrated circuit needs to use to ensure that its electrical parameters meet the standards. The measured electrical characteristic data will be used to improve the efficiency of the semiconductor manufacturing process and product performance (not to detect defective products).2) Wafer Aging TestThe semiconductor defect rate comes from two aspects, namely, the rate of manufacturing defects (higher in the early stage) and the rate of defects occurring throughout the life cycle afterwards. Wafer aging test refers to testing the wafer under a certain temperature and AC/DC voltage to find out which products may have defects in the early stage, that is, to improve the reliability of the final product by discovering potential defects.3) Parameters TestTemp TestHigh TemperaturVerify that the chip can work at a temperature that exceeds the maximum temperature by 10% or higher.Low TemperaturVerify that the chip can work at a temperature that lower the minimum temperature by 10% or more.Room TemperaturCheck whether the chip can work at room temperature (25°C).The high and low temperature test requirements for storage semiconductors are 85-90℃ and -5-40℃ respectively.Speed TestCoreCheck whether the core functions are valid.SpeedTest movement speed.Motion TestDCApply direct current to check whether the current and voltage are normal.ACApply alternating current to test movement characteristics.FunctionCheck whether all functions are normal.4) RepairRepairing is the most important test step, because some defective chips can be repaired, and you only need to replace the defective components.5) InkThe chips that failed the electrical test have been sorted out in the previous steps, but they still need to be marked to distinguish them. In the past, we needed to mark defective chips with special inks to ensure that they can be identified with the naked eye. Today, the system automatically sorts them based on the test data values. Ⅷ PackageSquare chips (also called single wafers) of equal size are formed on the wafers processed by the previous several processes. The next thing to do is to obtain individual chips by cutting. The chip that has just been cut is very fragile and cannot exchange electrical signals, so it needs to be processed separately. This process is packaging, including forming a protective shell on the outside of the semiconductor chip and allowing them to exchange electrical signals with the outside. The entire packaging process is divided into five steps, namely wafer sawing, single wafer attachment, interconnection, molding, and packaging testing.1) Wafer SawingTo cut countless densely arranged chips from the wafer, we must first grind the back of the wafer until its thickness can meet the needs of the packaging process. After grinding, we can cut along the scribing line on the wafer until the semiconductor chip is separated.There are three types of wafer sawing techniques: blade cutting, laser cutting and plasma cutting. Blade cutting refers to cutting wafers with diamond blades, which is prone to generate frictional heat and debris and thus damage the wafers. Laser cutting has higher precision and can easily handle wafers with thin thickness or small scribing line pitch. Plasma cutting uses the principle of plasma etching, so even if the scribing line pitch is very small, this technology can also be applied.2) Single Wafer AttachmentAfter all the chips are separated from the wafer, we need to attach the individual chips (single chip) to the substrate (lead frame). The role of the substrate is to protect the semiconductor chips and allow them to exchange electrical signals with external circuits. A liquid or solid tape adhesive can be used to attach the chip.3) BondFigure 15. BondingAfter attaching the chip to the substrate, we also need to connect the contact points of the two to achieve electrical signal exchange. There are two connection methods that can be used in this step: wire bonding using thin metal wires and flip chip bonding using spherical gold or tin blocks. Wire bonding is a traditional method, and flip-chip bonding can speed up semiconductor product manufacturing.4) MoldingFigure 16. MoldingAfter completing the connection of the semiconductor chip, it is necessary to use a molding process to add a package to the outside of the chip to protect the semiconductor integrated circuit from external conditions such as temperature and humidity. After the packaging mold is made as required, we put the semiconductor chip and the epoxy molding compound (EMC) into the mold and seal it. The sealed chip is in its final product.5) Package TestThe chip that has the final form must pass the final defect test. All that enters the final test is the finished semiconductor chip. They will be put into the test equipment, set different conditions such as voltage, temperature and humidity, etc. for electrical, functional and speed tests. The results of these tests can be used to find defects, improve product quality and production efficiency. Frequently Asked Questions about Semiconductor Manufacturing Steps1. What is a semiconductor and how is it made?Semiconductors are made from materials that have free electrons in their structure that can move easily between atoms, which aids the flow of electricity. ... Silicon has four electrons in its outer orbital, which allows the covalent bonds to form a lattice and thus form a crystal. 2. How many steps are in a manufacturing semiconductor?In semiconductor device fabrication, the various processing steps fall into four general categories: deposition, removal, patterning, and modification of electrical properties. 3. How is semiconductor manufactured?In the manufacturing process of IC, electronic circuits with components such as transistors are formed on the surface of a silicon crystal wafer. A thin film layer that will form the wiring, transistors and other components is deposited on the wafer (deposition). The thin film is coated with photoresist. 4. What type of operation is semiconductor processing?In semiconductor device fabrication, the various processing steps fall into four general categories: Deposition, Removal, Patterning, and Modification of electrical properties. Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. 5. What chemicals are used in semiconductor manufacturing?Semiconductors chemstry is mainly organized around the chemical treatment by solvents and acido-basic attacks of semiconductors. Chemistry of solvents : the main chemicals used during this stage are trichloroethylene, acetone, isopropanol and also other alcohols such as denatured ethanol.

What is a Laser Diode?A laser diode (injection laser diode, or diode laser) is a semiconductor device that can generate laser light, emitting a narrow light containing a single color, which is similar to a light-emitting diode (LED). The three conditions for generating laser light are: achieving particle number inversion, meeting threshold conditions and resonance conditions. Since laser diodes are extremely electrostatic sensitive, they should be used with care to prevent static electricity. They can be divided into homojunction laser, single heterojunction (SH) laser, double heterojunction (DH) laser and quantum well (QW) laser according to the different PN junction materials.Topics Covered in this GuideLaser Diode Tech Guide in 2021What is a Laser Diode?Laser Diode SpecificationsLaser Diode CharacteristicsLaser Diode ApplicationsHow Does a Laser Diode Work?What is the Laser Diode Symbol?What are the types of Laser Diode?Laser Diode Using TipsHow to Test a Laser Diode?How to Make a Laser Diode?How to Power a Laser Diode?How to Build a Laser Diode Driver Circuit?How to Wire a Laser Diode?How to Select the Right Laser Diode?How to Drive Pulse Laser Diode?What is Power Source of 532 Laser Diode?What is the Difference between Laser Diode(LD) and LED?What is the Wavelength Range of a Laser Diode?Is Diode Laser Permanent?Is LED a Laser Light?How Long do Diode Lasers Last?Can an LED be Used as a Laser?What are the Advantages of Using Laser Diode Instead of an LED?What is the Disadvantage of Laser?FAQsLaser Diode Specifications(1) Wavelength– It is the laser tube working wavelength, including 635nm, 650nm, 670nm, 690nm, 780nm, 810nm, 860nm, 980nm, etc, used for photoelectric switch laser.(2) Threshold Current– The current at which the laser tube starts to generate laser oscillation. For general low-power laser tubes, the value is about tens of mA, and the threshold current of laser tubes with multi-quantum well structure can be as low as 10mA or less.(3) Operating Current– It is the drive current that laser tube to achieve the rated output power, which is more important for the design and commissioning of the laser drive circuit.(4) Vertical Divergence Angle– It is the open angle that the laser diode's light-emitting band in the direction of the vertical PN junction, generally in the 15˚ ~ 40˚ or so.(5) Horizontal Divergence Angle– It is open angle that the laser diode's light-emitting band in the parallel direction with the PN junction, generally in 6˚ ~ 10˚ or so.(6) Monitoring Current– It is the current flowing on the PIN tube when the laser tube is at rated output power. Laser Diode CharacteristicsThe basic structure of the semiconductor laser diode is shown in the figure. A pair of parallel planes perpendicular to the PN junction surface form the Fabry-Perot resonant cavity, they can be the solution surface of the semiconductor crystal, but also can be polished plane. The remaining two sides are relatively rough to eliminate the laser action in other directions than the main direction. In addition, lasers consist of three main components: a lasing medium (solid, liquid or gas), a stimulating energy source (pump) and an optical resonator.Figure 1. Semiconductor Laser Diode StructureOne of the characteristics of laser diodes is the ability to modulate the intensity of their output light directly from current. Because the relationship between output optical power and input current is mostly linear, laser diodes can use analog or digital current to directly modulate the output light intensity, no need for expensive modulators, which makes the diode more economical to use.The most important characteristic of a diode is its unidirectional conductivity, and laser diodes, as one of the diode types, have the same features. In a circuit, current can only flow in from the positive terminal of the diode and out from the negative terminal. The following are specific descriptions.1) Forward FeatureIn electronic circuits, the diode conducts when the positive terminal of the diode is connected to the high potential terminal and the negative terminal to the low potential terminal. In terms of this connection, it called forward bias. In addition, when the forward voltage applied to both ends of the diode is very small, the diode still cannot conduct and the forward current flowing through is very small. Only when the forward voltage reaches a certain value (this value is called the "threshold voltage", about 0.2V for germanium tubes and 0.6V for silicon tubes), the diode can conduct. After it, the voltage across the diode remains basically unchanged (about 0.3V for germanium and 0.7V for silicon diode), which is called the "forward voltage drop".2) Reverse FeatureIn electronic circuits, the positive terminal of the diode is connected to the low potential terminal, and the negative terminal is connected to the high potential terminal. When there is almost no current flowing through the tube, the diode is in the cutoff state. This connection called reverse bias. Diode in reverse bias, there will still be a weak reverse current flow through, called leakage current. When the reverse voltage across the diode increases to a certain value, the reverse current will increase sharply, the diode will lose its unidirectional conductive characteristics, this state is called diode breakdown. Laser diode injection current must be greater than the critical current density, which is related to the temperature of the contact surface and indirectly affects the tube performance, to meet the residence reversal conditions and emit laser. When operating at high temperatures, the critical current increases, reducing efficiency and even damaging the component. Laser Diode ApplicationsAs the most common type of laser products, laser diodes have the advantages of high efficiency, small size and long life, but their low output power (generally less than 2mW), poor linearity and monochromaticity are not good for cable TV system applications, because they cannot transmit multi-channel and high-performance analog signals. Based on the advantages of laser diodes, they play a important role in many applications areas. For example, in the return module of bi-directional optical receivers, uplink transmission generally uses quantum well laser diodes as the light source. Also it is widely used in the computer on the CD-ROM drive, laser printer in the print head, bar code scanner, laser ranging, laser medical, optical communications, laser indication and other small power optoelectronic equipment. The lighting, laser surgery, laser welding and laser weapons and other high-power equipment have laser diodes too.Compared with LEDs, With different light source, lasers are more powerful and operate at faster speeds than LEDs, and they can also transmit light farther with fewer errors. They are also much more expensive than LEDs.Figure 2. Laser DiodeHow Does a Laser Diode Work?Light Emitting PrincipleLight emission in semiconductors is usually caused by carrier complexation. When a positive voltage is applied to the PN junction, it will weaken the PN junction barrier, forcing electrons to be injected into the P region from the N region, and holes to be injected into the N region from the P region. These non-equilibrium electrons and holes injected near the PN junction will be compounded, thus emitting photons of wavelength λ with the following equation.λ=hc/EgWhere: h - Planck's constant, c - speed of light, Eg - band gap width of the semiconductor.The above luminescence phenomenon due to the spontaneous compounding of electrons and holes is called spontaneous radiation. When the spontaneous radiation generated by the photon through the semiconductor, once the electron-hole pair has been emitted near, it can excite the two composite to generate new photons. This photon has been induced to excite the carrier compound and issued a new photon known as excited radiation.If the injection current is large enough, a carrier distribution opposite to the thermal equilibrium state will be formed, that is, the particle number reversal. When the carrier within the active layer in the case of a large number of inversion, a small amount of spontaneous radiation generated by the photons due to the resonant cavity two end reflect and then have induction radiation, resulting in frequency-selective resonance positive feedback, or a gain for a frequency. When the gain is greater than the absorption loss, a coherent light with good spectral lines can be issued from the PN junction, that is, the laser.How Laser Diodes Work?As for Laser diode light-emitting principle, the P-N junction in a laser diode is formed by two doped GaAs layers. It has two flat-ended structures, parallel to a end (highly reflective surface) and a partial reflection. Laser diodes emit coherent light in which all the waves are at the same frequency and phase. The wavelength of the light to be emitted is exactly related to the length of the junction. When the P-N junction is forward biased by an external voltage, the electrons move through the junction and recombine as in a normal diode. When the electrons are compounded with holes, photons are released. These photons hit the atoms, causing more photons to be released. As the forward bias current increases, more electrons enter the depletion region and cause more photons to be emitted. Eventually, some of the photons randomly drifting in the depletion region strike the reflecting surface vertically, thus reflecting back along their original path. The reflected photons are again reflected back from the other end of the junction. This movement of photons from one end to the other is continuous several times. During the photon motion, more atoms release more photons due to the avalanche effect. This process of reflection and production of more and more photons produces a very intense laser beam.Each photon produced in the emission process explained above is identical to the other photons in terms of energy level, phase relationship and frequency. Thus, the emission process gives a laser beam of a single wavelength. To produce a laser beam, the current in the laser diode must be made to exceed a certain threshold level. Currents below the threshold level force the diode to behave as an LED, emitting incoherent light. What is the Laser Diode Symbol?The laser diode symbol used is often the same one used for light emitting diodes in circuit diagrams. It uses the basic semiconductor diode symbol with arrows indicating the generation and emanation of light.Figure 3. Laser Diode Symbol What are the types of Laser Diode?There are several types of laser diodes:✔️Quantum well lasers✔️Quantum cascade lasers✔️External-cavity diode lasers✔️Interband cascade lasers✔️Separate confinement heterostructure lasers✔️DHL (double heterostructure lasers)✔️DFB-LD (distributed feedback laser diode)✔️DBR-LD (distributed bragg reflector laser)✔️FBG (FBG laser diodes laser diodes)✔️VCSEL ( vertical-cavity surface-emitting laser)✔️VECSEL(vertical-external-cavity surface-emitting-laser)✔️MOEMS-LD (micro-opto-electro-mechanical systems laser diode) Laser Diode Using Tips1) laser diode emitted laser light may cause harm to the human eyes. When using, don’t directly watch the light source. It requires warning signs.2) The device needs a suitable drive power supply, the instantaneous reverse current should not exceed 2uA, and the reverse voltage should not exceed 3V. In the power supply on and off, to prevent inrush current. When testing the drive circuit with an oscilloscope, disconnect the power supply and then connect the oscilloscope probe, if the probe is tested under power on, the inrush current may damage the device.3) The device should be stored or worked in a clean environment.4) Working at higher temperatures will increase the threshold current, lower conversion frequency and accelerate the aging of the device. When adjusting the amount of light input, use the optical power meter to detect to prevent exceeding the large rated output.5) The output power works higher than the specified parameters, which will accelerate the aging of the components.The following measures can be taken to slow down device aging.    a. Driving the laser diode with a DC constant current source.    b. Connect a current limiting resistor in series with a bypass capacitor to the laser diode circuit.    c. Since an increase in the temperature of the laser diode will increase the current flowing through it, the heat dissipation measures must be applied to ensure that the device operates within a certain temperature range.(4) To avoid the laser diode breakdown due to withstand excessive reverse voltage, it can be connected in reverse parallel on both ends of the fast silicon diode.(6) The machine needs to be fully dissipated or used under cooling conditions to prevent high temperature use. The output wavelength of the laser is affected by the operating current and heat dissipation, to maintain good heat dissipation conditions and reduce the temperature of the tube core when working.7) Diodes are electrostatic sensitive devices, to take appropriate anti-static measures.Figure 4. Injection Laser DiodeHow to Test a Laser Diode?a. Resistance measurement methodRemove the laser diode, use a multimeter R × 1k or R × 10k file to measure its positive and negative resistances. If normal, the forward resistance value is between 20~40kΩ, and the reverse resistance value is ∞ (infinity). If the measured forward resistance value has exceeded 50kΩ, it means that the performance of the laser diode has declined. If the measured forward resistance value is greater than 90kΩ, it means that the diode has been seriously aged, can no longer be used.b. Current measurement methodUse a multimeter to measure the voltage drop across the load resistor in the laser diode drive circuit, and then estimate the current value flowing through the tube according to Ohm's law. When the current exceeds 100mA, if the laser power potentiometer is adjusted, and no significant change in current, the laser diode can be judged to be seriously aged. If the current increases sharply and out of control, it means that the optical resonant cavity of the laser diode has been damaged.c. Pins DetectionThe laser diode has three pins: LD transmitter, PD receiver, LD-N common1) To distinguish between LD and PD. Use R × 1k block to measure the resistances of laser diode three pins. If a resistance value between the two pins reaches a few thousand ohms, at this time, the black pen is connected to the end of the PD anode, the red pen is connected to the pin for the common terminal, the remaining pin for the LD cathode, so as to distinguish the PD part (bc part of the figure) and LD part ( This distinguishes the PD part (bc part of the figure) and the LD part (ab part of the figure).2) Detect the PD part. PD part of the laser diode is essentially a photosensitive diode, using a multimeter test method is as follows: R × 1k block to measure its resistance, if the forward resistance of a few thousand ohms, the reverse resistance is infinite, it initially indicates that the PD part is good. If the forward resistance is 0 or infinity, it shows that the PD part has been bad. If the reverse resistance is not infinity, it means that the PD part has reverse leakage and the tube quality has become poor.3) Detect the LD part. Use the multimeter R × 1k block to measure the forward resistance of the LD part, that is, the black pen connected to the common terminal b, red pen connected to the a, the forward resistance should be between 10kΩ ~ 30kΩ, the reverse resistance should be infinity. If the measured forward resistance value is greater than 55kΩ, the reverse resistance value of 100kΩ or less, indicating that the LD part has been seriously aging, so the use of the effect will become worse. How to Make a Laser Diode?Step 1: Before made a laser diode, you should clear somethings firstly, including safety equipment, procedures, training in place, as well as disposal etc. Step 2: Build a working laser yourself you start with buying the diode. then you need a lens , and a heat sink , and a powersupply that won't blow it (they're very sensitive) .... all these components are on online, and that's quiet a tricky job ...much easier and cheaper to buy an assembled laser.Step 3: Spend a couple of pounds to purchase a laser pointer, and pull the diode & circuit out of that.Step 4: Don't power it up when it's direction is not firmly fixed away from your eyes, from anyone's eyes , and there might be reflective surfaces on the beam path nearby. Pay attention, do it legally where you are. How to Power a Laser Diode?Laser diodes are operated in forward conduction mode within a specified current range that is optimal for lasing operation, because they are current-driven devices. Laser diode power supplies can operate in one of two modes, constant current (CC) and automatic power control (APC). Most, but certainly not all, smaller laser diodes (5.6- and 9-mm packages) are operated in APC mode. For APC operation, the power supply must have a photodiode mounted inside the laser diode package. How to Build a Laser Diode Driver Circuit?Firstly, you should know that a laser diode driver circuit is a circuit which is used to limit the current and then supplies to the laser diode, and then follow the below steps:Step 1: Have a project with laser diode.Step 2: Find out all the useful parts and their parameters from your project.Step 3. Build the circuits according to the related project schematic.Step 4. Connect the Laser Diode and test it. How to Wire a Laser Diode?According to unidirectional conductivity, laser diodes only allow current to flow in one direction, and they're always polarized. First look at the positive and negative poles of the diode, and then the positive potential is connected to the anode of the diode, and the negative potential is connected to the cathode of the diode. How to Select the Right Laser Diode?Choose a laser diode for your application according to the following steps:Step 1: Turn application requirements into laser parametersStep 2: Selecting the laser typeStep 3: Selecting the laser materialStep 4: Make your final chart and go searching How to Drive Pulse Laser Diode?Laser Diode Driver is to provide current to the laser diode. With the amount of current controlled by the user or some automatic apparatus, you can drive a pulse laser diode. In addition, a laser driver can only regulate the current as long as the laser voltage stays within certain limits, so you should have a check the circuit parameters to select a proper diode driver. What is Power Source of 532 Laser Diode?Check the following table to find out the power source of 532 laser diode:532nm Green Laser DiodePowerPackageDescription0.004WTO-Can- Integrated Photodiode- Compact Size0.005WTurn-Key Module- Compact Size- Long Lifetime0.01WTurn-Key Module- Fiber-Coupled Output- Integrated Photodiode0.1WTO-Can- Integrated Photodiode- Compact Size0.2WTO-Can- Integrated Photodiode- Mode-Hop Supression0.4WButterfly- Integrated Photodiode- Integrated Heater0.5WButterfly- Internal Heater- Integrated PhotodiodeWhat is the Difference between Laser Diode(LD) and LED?LDs and LEDs both emit photons to produce light, but both of them have many differences according to the following table:ParametersLDLEDWorking PrincipleStimulated emissionSpontaneous emissionOmnidirectional emissionFull FormLight Amplification by Stimulated Emission of RadiationLight Emitting DiodeResponseFast response in comparison to LEDSlow responseDriving CurrentRanges from 5 to 40mARanges from 50 to 100mANature of Emitted LightCoherent and MonochromaticIncoherent and consists of various colors.Junction Area during ManufacturingNarrow and small JunctionWide Junction AreaBandwidth RangeRanges from 1MHz to 2MHZRange from10 to 50THzPower to light Conversion EfficiencyApprox 70 %Approx 30%Numerical Aperture of the obtained Light BeamExtremely low as compared to LEDs.Higher in LEDsCostHigh cost and thus used in the specific application.Low cost and thus economicalWhat is the Wavelength Range of a Laser Diode?Diode lasers deliver wavelengths ranging from 810 to 1064 nm. Diode lasers are compact and portable solid-state units. They are used strictly for soft tissue procedures and penetrate 2 to 3 mm or more into soft tissue, depending on the wavelength and tissue biotype. Is Diode Laser Permanent?Diode lasers use a single wavelength of light that has a high abruption rate in melanin. As the melanin heats up it destroys the root and blood flow to the follicle disabling the hair growth permanently. ... Diode lasers deliver high frequency, low fluence pulses and can be safely used on all skin types. Is LED a Laser Light?LEDs typically last longer than lasers, while lasers are faster. ... LEDs have a higher output with wider bandwidths, meaning that they can produce a broad range of less-concentrated light. Lasers have a lesser output and a small bandwidth, produced with a tiny pinpoint of light. How Long do Diode Lasers Last?Typical lifetime of laser diode modules are 25,000 to 50,000 hours. If the laser diode temperature continues to rise exceeding the maximum operating temperature, the diode can be catastrophically damaged or the long term performance may degrade significantly. Can an LED be Used as a Laser?The LED and laser emit light in a relatively narrow range of wavelengths. However, lasers put all their energy in a single wavelength, which emits from a tiny spot. LEDs spread the energy over more wavelengths and send that light from a larger spot into wide cone. What are the Advantages of Using Laser Diode Instead of an LED?It produces a very intense beam of light or infrared radiation which is having following properties. Laser diode used in optical fiber systems are made of gallium arsenide phosphide. The laser having size of grain of sand can produce power output of about 10 mWatt. ON/OFF switching speed of laser is faster than LED. What is the Disadvantage of Laser?Following are the drawbacks or disadvantages of Laser:It is expensive and hence more expenditure to the patients requiring laser based treatments.It is costly to maintain and hence more cost to doctors and hospital management. Increases complexity and duration of the treatment based on laser devices or equipments. FAQs1. Why do we prefer GaAs for laser diode?GaAs advantagesGaAs devices are relatively insensitive to overheating, owing to their wider energy band gap, and they also tend to create less noise (disturbance in an electrical signal) in electronic circuits than silicon devices, especially at high frequencies. 2. What is the advantage of laser over LED?The output power of a 1 watt LED can be < 100 milliwatts. Besides dramatic differences in total output, the laser also offers a significant advantage in terms of how usable that power is to the optical system. Specifically, the laser is a point source of coherent light that produces a well-behaved beam. 3. Why is laser light monochromatic?Monochromatic Laser LightThe light from a laser typically comes from one atomic transition with a single precise wavelength. So the laser light has a single spectral color and is almost the purest monochromatic light available. 4. What happens if the laser diode is forward biased?Forward bias injects charges into the junction, causing spontaneous emission of photons. When the diode is forward-biased, charges are injected into the active area of the junction, while electrons and holes recombine in the junction, creating spontaneous emission of photons. 5. Is a laser diode an LED?Light-emitting diodes (LEDs), like laser diodes, generate radiation via electrical current injection into a junction. LED light comes from spontaneous emission, whereas laser diode light arises from stimulated emission. Thus, LEDs generally have lower output powers and omnidirectional emission.

IntroductionThe transistor is one of the basic semiconductor components, which has the function of current amplification in electronic circuit. It is made of two PN junctions very close to each other on a semiconductor substrate. Two PN junctions divide the entire semiconductor into three parts: The middle part is the base area, and the two sides are the emitter and the collector. What is NPN Transistor? For BeginnerCatalogIntroductionⅠ NPN Transistor Arrangement and SymbolⅡ How Do NPN Transistors Work?Ⅲ NPN Transistor Uses: A Controllable ValveⅠ NPN Transistor Arrangement and SymbolBefore explaining the principle, let's first understand the basic structure and symbols of the NPN transistor. To identify the NPN transistor pins, it will be Collector (c), Base (b) and Emitter (e).Figure 1. NPN Transistor Structure and SymbolNPN transistor is composed of two N-type semiconductors and one P-type semiconductor. Generally, an NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). The arrangement is shown in the Figure 1. Ⅱ How Do NPN Transistors Work?Here is the main description to illustrate the basic principle and function of NPN transistors.1) Current AmplificationThe following analysis is only for NPN silicon transistors. As shown in the figure above, we call the current flowing from the base B to the emitter E the base current Ib; the current flowing from the collector C to the emitter E is called the collector current Ic. The directions of these two currents are both flowing out of the emitter, so an arrow is used on the emitter E to indicate the current direction.The amplification function of the transistor is: the collector current is controlled by the base current (assuming that the power supply can provide a large enough current to the collector), and a small change in the base current will cause a large change in the collector current: the change in the collector current is β times the change in the base current, that is, the current change is amplified by β times, so we call β the magnification of the transistor (β is generally much larger than 1). If we add a changing small signal between the base and the emitter, it will cause a change in the base current Ib. After the change in Ib is amplified, it leads to a big change in Ic. If the collector current Ic flows through a resistor R, it can be calculated according to the Ohm's Law formula U=R*I, and the voltage on this resistor will change greatly. According to the voltage on this resistor, so we can get the amplified voltage signal. In short, the change satisfies a certain proportional relationship.2) Bias CircuitWhen the transistor is used in the actual amplifier circuit, it is also necessary to add a suitable bias circuit. There are several reasons for this. First of all, due to the non-linearity of the transistor's BE junction (equivalent to a diode), the base current must be generated after the input voltage reaches a certain level (for silicon tubes, 0.7V is often used). When the voltage between the base and the emitter is less than 0.7V, the base current can be considered as zero. However, in practice, the signal to be amplified is often much smaller than 0.7V. If no bias is applied, such a small signal is not enough to cause a change in the base current (because when it is less than 0.7V, the base current is all 0).Add a suitable current to the base of the transistor (called the bias current, and the resistor in the figure used to provide this current, is called the base bias resistor). When a small signal follows this bias current are superimposed together, a small signal will cause a change in the base current, and the change in the base current will be amplified and output on the collector. Another reason is meeting the requirement of the output signal range. If there is no bias, then only those increased signals will be amplified, but the decreased signals will be invalid (because the collector current is 0 when there is no bias, and it cannot be reduced). With bias, let the collector have a certain current in advance. When the input base current becomes smaller, the collector current can be reduced; when the input base current increases, the collector current increases. Both the reduced signal and the increased signal can be amplified.3) NPN Transistor SwitchLet's talk about the saturation mode of the transistor. As shown in the figure above, because of the limitation of resistance Rc (Rc is a fixed value, then the maximum current is U/Rc, where U is the power supply voltage), the collector current cannot increase indefinitely. When the base current increases and the collector current cannot continue to increase, the transistor enters a saturated state. The general criterion for judging whether the transistor is saturated is: Ib*β>Ic.In a saturation state, the voltage between the collector and the emitter of the transistor will be very small, which can be understood as a switch. In this way, when the base current is 0, the collector current is 0 (this is called the triode cut-off), which is equivalent to the switch off; when the base current is large, it is equivalent to the switch on. In cut-off and saturation state, a transistor is equal to a switch.4) Operational StateIf we replace the resistor Rc with a bulb in the above figure, then when the base current is 0, the collector current is 0, so the bulb is off. If the base current is relatively large (greater than the current flowing through the bulb divided by the magnification β), the transistor will saturate, and the bulb will light up. Since the control current only needs to be a little larger than β of the bulb current, a small current can be used to control the on and off of a large current. If the base current increases slowly, the brightness of the bulb will also increase (which is a saturation process).The figure below is a basic transistor switch circuit. The base should connect a base resistor (R2), and the collector connects with a load resistor (R1).Operational ModeNPNCut-offUne<UonUc>UbActiveUbe>UonUc>UbSaturationUbe>UonUc<UbNPN transistor uses the B-E current (IB) to control the C-E current (IC). The E pole has the lowest potential, and usually the C pole has the highest potential during normal amplification, that is, VC>VB>VE.NPN base extremely high voltage, the collector and emitter are short-circuit and low-voltage, and the collector and emitter are open-circuit.NPN is suitable for two situations:If the input is a high level and the output needs a low level, NPN is better.If the input is a low level and the output needs a high level, NPN is better.2N2222 NPN Transistor PinoutⅢ NPN Transistor Uses: A Controllable ValveNPN is a component that uses b (base) current Ib to drive the current Ic flowing through CE, and its working principle is much like a controllable valve.Figure 2. A Controllable ValveThe blue water flow in the thin pipe on the left impacts the lever to open the valve of the large water pipe, allowing the larger red water flow to pass through the valve. The larger the blue water flow, the greater the red water flow in the big pipe. If the magnification is 100, then when the blue water flow is 1 kg/hour, then 100 kg/hour of water is allowed to flow through the large pipe. The principle of the transistor is the same. When Ib (base current) is 1mA, a current of 100mA is allowed to pass through Ice.Figure 3. NPN Transistor DiagramLet's analyze this circuit. If its magnification is 100, and ignore the base voltage. The base current is 10V÷10K=1mA, so the collector current should be 100mA. According to Ohm's law, the voltage on Rc is 0.1A×50Ω=5V. Then the remaining 5V is on the C and E poles of the transistor. Now if we let Rb be 1K, then the base current is 10V÷1K=10mA, according to the magnification of 100, is Ic 1000mA? If it is really 1A, then the voltage on Rc is 1A×50Ω=50V. The power supply voltage has been exceeded, and the transistors have become generators? This is not the case. See below:Figure 4. NPN Transistor Compared to A ValveContinue the metaphor. When the control current is 10mA, the valve on the main water pipe is opened to allow 1A current to flow, but can 1A be realized? No, because there is a resistor on it, it is equivalent to a fixed valve. It is stringed on top of the main water pipe. When the opening of the lower controllable valve is greater than the opening of the upper fixed resistor, the water flow will not increase any more, but will be equal to the water flow passing through the fixed valve opening above. Therefore, it is useless to open the lower transistor to a large opening. Therefore, we can calculate the maximum current of the fixed resistor 10V÷50Ω=0.2A, which is 200mA. That is to say, in the circuit, the base current increases and the collector current also increases. When the base current Ib increases to 2mA, the collector current increases to 200mA. When the base current increases again, the collector current will no longer increase, and it will not move at 200mA. At this time, the upper resistor also acts as a current limiter.  Let us understand the status of the IO in the microcontroller.Figure 5. AT89S51/52 The circuits with 24 IO ports of P1-P3 in the single-chip microcomputer are as shown in the figure above. Usually the purpose of using electronic circuits is to allow devices to obtain a certain current to make them work. For example, to make light-emitting diodes bright, a current of more than 1mA is generally required. However, the single-chip microcomputer is a smart chip. It can make logical analysis and judgments by detecting the voltage value of each IO port, and outputs high or low voltage as the result signal. Therefore, it can be seen that the IO ports of the single-chip microcomputer focus on voltage, not the current flowing through R and the transistor. Here what is the relationship between the voltage and current of the IO port in the single-chip microcomputer?  Continue the water pipe example.Suppose we let the valve of R open larger and let the control valve below be fully closed. At this time, as shown in Figure 6, it can be seen that the pressure at point P is the same as the water tank. When we fully open the following control valve, as shown in Figure 7, the water will flow through the pipeline with a large flow, and the pressure at point P is 0 at this time. This principle is very similar to electronic circuits. The logic quantity measured at the output point P is 1 (power supply voltage) or 0 (0 potential) by transistor turning off or on. However, there is a problem with this process, that is, when the output of point P is required to be 0, the transistor will be turned on very large, and the current flowing through it will be very large. There are 32 IO ports on the single-chip microcomputer, which consumes a lot of power. Look at Figure 8. If we close the upper valve R very small and close the lower control valve fully, then the pressure at point P will still the same as the water tank, which is the same as in Figure 6 above. When we open the control valve greatly, as shown in Figure 9, although the pressure at point P is also 0, the flow of water passing through at this time is greatly reduced. In this way, we can either output 1 or 0. So very little water is consumed. The circuit in the single-chip microcomputer does exactly this. The resistance R on it is about 50K, and the maximum current is 5V÷50K=0.1mA. In other words, when P outputs 1, no current is consumed, and when P outputs 0, the current consumed is 0.1mA. Because of its large pull-up resistance R, for beginners, it is necessary to have certain methods to directly drive LEDs or other loads. Here to share the various situations when the IO port is connected to the load.Figure 10. AT89S51/52 & 74HC373Let's take a look at the situation of connecting TTL devices first. When P1.0 is connected to an input pin of 74HC373, and the input impedance of TTL is very high, about a few hundred K to M ohm level. We assume 500K resistor to P1.0 to ground. In this way, when the transistor is turned on, the P1.0 point is at a low level, and a current of 0.1mA flows through Rc and then through the transistor to the ground, and no current flows through Ri. When the transistor is cut off, the current flows through Rc and then flows to the ground through Ri. Due to the resistor voltage divider effect, there are partial voltages on Rc and Ri, and the voltage at point P1.0 is the divided voltage of Rc and Ri. Total current is 5V÷(50K＋500K)=0.009mA, then the voltage at point P1.0 is 0.009mA×500K=4.5V. TTL stipulates that output 2.4~5V is high level. So this connection is correct. Now let's take a look at the situation of using S51 to drive the LED.AT89S51 Correct ConnectionLet’s take a look at the situation in Figure 11. Obviously, only P1.0 is a high potential to light the luminous tube, so the transistor must be cut off. In this case, the current flows through Rc to the luminous tube and then to the ground. To make the luminous tube turn on, there must be a threshold voltage exceeding 2.1V at both ends of the luminous tube. Therefore, the current flowing through the luminous tube is (5V-2.1V)÷50K=0.058mA, which is too weak to conduct.Look at Figure 12. It can be seen from the figure that P1.0 must be at a low potential if the luminous tube turned on. The transistor of the P1.0 port must be turned on. At this time, the current flows all the way through Rc to the transistor and then to the ground. The other way consumes 2.1V on the luminous tube. Then current flows through with almost no resistance, but the maximum current of the triode of the IO port cannot exceed 15mA. If it exceeds, the triode will be burned out, so this connection method is incorrect. So how can these two connections be able to drive the light-emitting tube? See below: AT89S51 Incorrect ConnectionLooking at Figure 13, a resistor Ri is connected between P1.0 and Vcc. When the transistor is turned on, two currents will flow through its c, e pole, one is the 0.1mA current on the internal R, and the other is the current on Ri. In order to prevent the transistor from over-current and burn out, we must make sure the resistance value, Ri=5V÷15mA=0.333K, which is about 330 ohms. At this time, the current flowing through the transistor is about 15mA, and the light-emitting tube is not bright at this time. When the transistor is turned off, both currents will flow through the luminous tube. The current flowing through the internal resistance of S51 is (5V-2.1V)÷50K=0.06mA, which is so small that we can ignore it. The current flowing through Ri is (5V-2.1V)÷330Ω=0.0087A, which is 8.7mA. However, the current consumed when the luminous tube is off is greater than the current consumed when the luminous tube is on. If many IO ports are used to light up many LEDs, such a circuit is not economical.Look at Figure 14, after connecting a resistor in series with the luminous tube between Vcc and P1.0. When the transistor is turned on, the two currents will flow through the c, e after confluence. The current on the internal resistance is still 0.1mA. The current on the ce should be less 15mA. If exceeds 15mA, the resistance is determined as (5V-2.1V) ÷ 15mA = 0.193K, which is about 200 ohms. In this way, the current flowing through the luminous tube is about 15mA, and the luminous tube is on. When the transistor is cut off, it blocks the paths of these two currents, so no current is consumed. Low level P1.0 directly drives the light-emitting tube. It can be seen that this circuit consumes 15mA of current when the light-emitting tube is on, and does not consume current when it is off, so this circuit is effective. S51 direct drive digital tube generally also uses this principle. Frequently Asked Questions about NPN Transistor1. What is meant by NPN transistor?An NPN transistor is the most commonly used bipolar junction transistor, and is constructed by sandwiching a P-type semiconductor between two N-type semiconductors. An NPN transistor has three terminals– a collector, emitter and base. The NPN transistor behaves like two PN junctions diodes connected back to back. 2. How do NPN transistors work?The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter "emits" electrons into the base, which controls the number of electrons the emitter emits. ... The transistor is kind of like an electron valve. 3. What is a NPN transistor used for?NPN transistors are mainly used in switching applications. Used in amplifying circuit applications. Used in the Darlington pair circuits to amplify weak signals. NPN transistors are used in the applications where there is a need to sink a current. 4. Which is better PNP or NPN transistor?A NPN transistor has electrons as majority charge carriers whereas the PNP transistor has holes as majority charge carrier. ... mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that's why they are preferred. 5. What does NPN mean?NPN stands for Negative, Positive, Negative. Also known as sinking.

When it comes to low-power, high-current, and ultra-high-speed semiconductor devices, many electronics hobbyists or engineers must first think of Schottky diodes (SBD). But do you really know how to use Schottky diodes? Compared with other diodes, what is special about Schottky diodes? This article will answer these questions for you and introduce Schottky diodes in details. This short video gives a brief introduction to Schottky Diode Catalog I. Schottky Diode Brief Introduction II. How does Schottky Diode Work? III. The Structure of Schottky Diode IV. How to Test Schottky Diode? V. Pros and Cons of Schottky Diode VI. Where to Use Schottky Diode? VII. How to Use Schottky Diode Correctly? FAQ I. Brief Introduction to Schottky Diode  Schottky diodes are named after their inventor, Dr. Schottky. The full name is: Schottky RecTIfier Diode (abbreviated as SR), also called: Schottky barrier diode, or SBD.   Schottky diode is a low-power, ultra-high-speed semiconductor device. The most notable feature is its extremely short reverse recovery time (can be as small as a few nanoseconds), and the forward voltage drop is only about 0.4V. It is mostly used as high-frequency, low-voltage, high-current rectifier diodes, freewheeling diodes, protection diodes, and also useful as rectifier diodes and small-signal detector diodes in circuits such as microwave communications. It is more common in communication power supplies, inverters, etc.   A typical application of Schottky diodes is in the switching circuit of a bipolar transistor BJT. By connecting a Shockley diode to the BJT to clamp, the transistor is actually close to the off state when the transistor is on, thereby improving the transistor’s performance. Switching speed. This method is a technique used in the TTL internal circuits of typical digital ICs such as 74LS, 74ALS, and 74AS.   The biggest feature of Schottky diodes is that the forward voltage drop VF is relatively small. In the case of the same current, its forward voltage drop is much smaller. In addition, its recovery time is short. It also has some shortcomings: the withstand voltage is relatively low, and the leakage current is slightly larger. It must be fully considered when selecting. II. How does Schottky Diode Work? Schottky diodes are metal-semiconductor devices made of precious metals (gold, silver, aluminum, platinum, etc.) A as the anode and N-type semiconductor B as the cathode. The barrier formed on the contact surface of the two has rectification characteristics.   Because there are a large number of electrons in N-type semiconductors, and there are only a small amount of free electrons in noble metals, electrons diffuse from the high concentration of B to the low concentration of A. Obviously, there are no holes in metal A, and there is no diffusion movement of holes from A to B.   As electrons continue to diffuse from B to A, the electron concentration on the surface of B gradually decreases, and the electrical neutrality of the surface is destroyed, so a potential barrier is formed, and the direction of the electric field is B→A. But under the action of this electric field, the electrons in A will also produce a drifting movement from A→B, thereby weakening the electric field formed by the diffusion movement.   When a space charge region with a certain width is established, the drifting movement of electrons caused by the electric field and the diffusion movement of electrons caused by different concentrations reach a relative balance, forming a Schottky barrier.   The internal circuit structure of a typical Schottky rectifier is based on an N-type semiconductor, and an N-epitaxial layer with arsenic as a dopant is formed on it. The anode uses materials such as molybdenum or aluminum to make a barrier layer. Use silicon dioxide (SiO2) to eliminate the electric field in the edge area and improve the withstand voltage of the tube.   The N-type substrate has a small on-state resistance, and its doping concentration is 100% higher than that of the H-layer. An N+ cathode layer is formed under the substrate, and its function is to reduce the contact resistance of the cathode. By adjusting the structural parameters, a Schottky barrier is formed between the N-type substrate and the anode metal.   When a forward bias is applied to both ends of the Schottky barrier (the anode metal is connected to the positive pole of the power supply, and the N-type substrate is connected to the negative pole of the power supply), the Schottky barrier layer becomes narrower and its internal resistance becomes smaller; on the contrary, if When reverse bias is applied to both ends of the Schottky barrier, the Schottky barrier layer becomes wider and its internal resistance becomes larger.   In summary, the structure principle of Schottky rectifier is very different from PN junction rectifier. The PN junction rectifier is usually called the junction rectifier, and the metal-semi-conductor rectifier is called the Schottky rectifier.   Aluminum-silicon Schottky diodes manufactured by the silicon plane process have also come out, which not only saves precious metals, but also Significantly reduce costs and improve the consistency of parameters. III. The Structure of Schottky Diode The structure and materials of the new high-voltage SBD are different from the traditional SBD. Traditional SBD is formed by contacting metal and semiconductor. The metal material can be aluminum, gold, molybdenum, nickel, titanium, etc., and the semiconductor is usually silicon (Si) or gallium arsenide (GaAs).   Since electrons have higher mobility than holes, in order to obtain good frequency characteristics, N-type semiconductor materials are selected as the substrate. In order to reduce the junction capacitance of the SBD and increase the reverse breakdown voltage without making the series resistance too large, a high-resistance N-thin layer is usually epitaxially on the N+ substrate.   CP is the parallel capacitance of the shell and tube, LS is the lead inductance, RS is the series resistance including the semiconductor body resistance and lead resistance, and Cj and Rj are the junction capacitance and junction resistance (both are functions of bias current and bias voltage), respectively.   As we all know, there are a large number of conductive electrons inside a metal conductor. When the metal is in contact with the semiconductor (the distance between the two is only an order of magnitude of the atom), the Fermi level of the metal is lower than the Fermi level of the semiconductor. At the sub-energy level corresponding to the conduction band of the semiconductor inside the metal, the electron density is less than that of the conduction band of the semiconductor.   Therefore, after the two contact, electrons will diffuse from the semiconductor to the metal, so that the metal is negatively charged and the semiconductor is positively charged. Since metal is an ideal conductor, negative charges are only distributed in a thin layer with the size of an atom on the surface.   For N-type semiconductors, the donor impurity atoms that have lost electrons become positive ions, which are distributed in a larger thickness. As a result of the diffusion and movement of electrons from the semiconductor to the metal, a space charge zone, self-built electric field and potential barrier are formed, and the depletion layer is only on the side of the N-type semiconductor (all the barrier zone falls on the semiconductor side).   The direction of the self-built electric field in the barrier zone points from the N-type region to the metal. With the increase of the thermionic self-built field, the drift current opposite to the diffusion current direction increases, and finally a dynamic equilibrium is reached, forming a contact potential between the metal and the semiconductor Barrier, this is the Schottky barrier.   When the applied voltage is zero, the diffusion current of electrons is equal to the reverse drift current, achieving dynamic equilibrium. When a forward bias is applied (that is, a positive voltage is applied to a metal and a negative voltage is applied to a semiconductor), the self-built field is weakened and the barrier on the semiconductor side is lowered, thus forming a positive current from the metal to the semiconductor.   When a reverse bias is applied, the self-built field increases, and the barrier height increases, forming a smaller reverse current from the semiconductor to the metal. Therefore, the SBD, like the PN junction diode, is a non-linear device with unidirectional conductivity. IV. How to Test Schottky Diode? Here we show you three testing method for three different diodes. 1. Detect low-power crystal diodes   A. Discrimination of positive and negative electrodes   (1) Observe the symbol mark on the housing. Usually the diode is marked with the symbol of the diode on the housing of the diode, one end with a triangular arrow is the positive electrode, and the other end is the negative electrode.   (2) Observe the color dots on the shell. The case of point contact diodes is usually marked with polar color points (white or red). Generally, the end marked with a colored dot is the positive electrode. Other diodes are marked with a color ring, and the end with the color ring is the negative electrode.   (3) Based on a measurement with a smaller resistance value, the end connected to the black test lead is the positive electrode, and the end connected to the red test lead is the negative electrode.   B. Detect the highest working frequency fM. The operating frequency of crystal diodes can be found in the relevant characteristic table. In practice, they are often distinguished by observing the contact wires inside the diode.    For example, point contact diodes are high-frequency tubes, and surface contact diodes are mostly low-frequency tubes. In addition, you can also use the multimeter R×1k block to test, generally the forward resistance is less than 1k high frequency tube.   C. Detect the highest reverse breakdown voltage VRM. For alternating current, because of constant changes, the highest reverse working voltage is also the peak alternating current voltage that the diode bears.   It should be pointed out that the highest reverse working voltage is not the breakdown voltage of the diode. Under normal circumstances, the breakdown voltage of the diode is much higher than the maximum reverse working voltage (about twice as high).   2. Detection of high frequency varistor diodes   A. identification diode positive and negative   The difference in appearance between high-frequency varistor diodes and ordinary diodes is that their color code is different. The color code of ordinary diodes is generally black, while the color code of high-frequency varistor diodes is light. Its polarity law is similar to that of ordinary diodes, that is, the end with the green ring is the cathode, and the end with the green ring is the anode.   B. Measure the forward and reverse resistance to judge whether it is good or bad   The specific method is the same as the method of measuring the forward and reverse resistance of ordinary diodes. When using a 500-type multimeter to measure the R×1k gear, the forward resistance of a normal high-frequency varistor diode is 5k～55k, and the reverse resistance is infinity.   3. Transient voltage suppression diode (TVS) detection   Use a multimeter to measure the quality of the tube. For a unipolar TVS, according to the method of measuring ordinary diodes, the forward and reverse resistance can be measured. Generally, the forward resistance is about 4kΩ, and the reverse resistance is infinite.   For the two-way polar TVS, the resistance between the two pins should be infinite when the red and black test leads are arbitrarily exchanged. Otherwise, the tube has poor performance or has been damaged. V. Pros and Cons of Schottky Diode Pros:  Schottky diodes have the advantages of high switching frequency and reduced forward voltage, but their reverse breakdown voltage is relatively low, mostly not higher than 60V, and the highest is only about 100V, which limits its application range.   Like in the switching power supply (SMPS) and power factor correction (PFC) circuit, the freewheeling diode of the power switch device, the high frequency rectifier diode of 100V or more used in the transformer secondary, the 600V～1.2kV high speed diode in the RCD snubber circuit, and For PFC boosting 600V diodes, only fast recovery epitaxial diodes (FRED) and ultra-fast recovery diodes (UFRD) are used.   The reverse recovery time Trr of UFRD is also above 20ns, which cannot meet the needs of 1MHz～3MHz SMPS in fields such as space stations. Even for SMPS with hard switching of 100kHz, due to the large conduction loss and switching loss of UFRD, the case temperature is very high, and a larger heat sink is required, which increases the size and weight of SMPS, which does not meet the requirements of miniaturization and lightness. Development trend.   Therefore, the development of high-voltage SBDs above 100V has always been a research topic and a hot spot of concern. In recent years, SBD has made breakthrough progress. High-voltage SBDs of 150V and 200V have been put on the market, and SBDs with more than 1kV made of new materials have also been successfully developed, thus injecting new vitality and vitality into their applications.   Cons:  The biggest disadvantage of Schottky diodes is their low reverse bias voltage and large reverse leakage current. For example, Schottky diodes using silicon and metal as materials have the highest reverse bias voltage rating. To 50V, and the reverse leakage current value is a positive temperature characteristic, it is easy to increase rapidly as the temperature rises, and it is necessary to pay attention to the hidden concern of thermal runaway in practical design.   In order to avoid the above-mentioned problems, the reverse bias voltage of the Schottky diode in actual use will be much smaller than its rated value. However, the technology of Schottky diodes has also progressed, and its reverse bias voltage rating can reach up to 200V. VI. Where to Use Schottky Diode? The structure and characteristics of SBD make it suitable for high-frequency rectification in low-voltage and high-current output occasions. It is used for detection and mixing at very high frequencies (such as X-band, C-band, S-band and Ku-band). Used as a clamp in high-speed logic circuits. SBD is often used in ICs. SBD*TTL integrated circuits have long become the mainstream of TTL circuits and are widely used in high-speed computers.   In addition to the characteristic parameters of ordinary PN junction diodes, SBD electrical parameters used for detection and mixing also include intermediate frequency impedance (referring to the impedance presented by the SBD to the specified intermediate frequency when the rated local oscillator power is applied, generally between 200Ω and 600Ω) , Voltage standing wave ratio (generally ≤ 2) and noise figure, etc. VII. How to Use Schottky Diode Correctly? Schottky diodes are widely used in circuits such as switching power supplies, frequency converters, and drivers. In different applications, different factors need to be considered, and different devices have different performances. Therefore, when selecting Schottky diodes, the following key parameters need to be considered comprehensively.   1. The conduction voltage drop VFVF is the voltage drop across the diode when the diode is forward-conducting. When the current through the diode is larger, the VF is larger; when the diode temperature is higher, the VF is smaller.   2. The reverse saturation leakage current IRIR refers to the current that flows through the diode when the reverse voltage is added to the two ends of the diode. The reverse leakage current of the Schottky diode is relatively large. The choice of Schottky diode is to choose a diode with a smaller IR as much as possible.   3. The rated current IF refers to the average current value calculated according to the allowable temperature rise during long-term operation of the diode.   4. The maximum surge current IFSM allows excessive forward current to flow. It is not a normal current, but an instantaneous current, which is quite large.   5. Even if the maximum reverse peak voltage VRM does not have reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later.   This reverse voltage that can be applied is not an instantaneous voltage, but a forward and reverse voltage repeatedly applied. Because the AC voltage is added to the rectifier, its maximum value is a specified important factor.   The maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. Currently Schottky's highest VRM value is 150V. FAQ 1. What is Schottky diode used for? Schottky diodes are used for their low turn-on voltage, fast recovery time and low-loss energy at higher frequencies. These characteristics make Schottky diodes capable of rectifying a current by facilitating a quick transition from conducting to blocking state. 2. What is the difference between Schottky diode and normal diode? In the normal rectifier grade PN junction diode, the junction is formed between P type semiconductor to N type semiconductor. Whereas in Schottky diode the junction is in between N type semiconductor to Metal plate. The schottky barrier diode has electrons as majority carriers on both sides of the junction. 3. How does Schottky diode work? In a Schottky diode, a semiconductor–metal junction is formed between a semiconductor and a metal, thus creating a Schottky barrier. The N-type semiconductor acts as the cathode and the metal side acts as the anode of the diode. This Schottky barrier results in both a low forward voltage drop and very fast switching. 4. What are the two important features of a Schottky diode? We have seen here that the Schottky Diode also known as a Schottky Barrier Diode is a solid-state semiconductor diode in which a metal electrode and an n-type semiconductor form the diodes ms-junction giving it two major advantages over traditional pn-junction diodes, a faster switching speed, and a low forward bias. 5. What is Schottky diode made of? Schottky diodes made from palladium silicide (PdSi)[clarification needed] are excellent due to their lower forward voltage (which has to be lower than the forward voltage of the base-collector junction). 6. Why Schottky is called hot carrier diode? When a Schottky diode is in unbiased condition, the electrons lying on the semiconductor side have a very low energy level when compared to the electrons present in the metal.Thus, the electrons cannot flow through the junction barrier which is called the Schottky barrier. If the diode is forward biased, electrons present in the N-side get sufficient energy to cross the junction barrier and enters the metal.These electrons enter into the metal with tremendous energy. Consequently, these electrons are known as hot carriers. Thus the diode is called a hot-carrier diode. 7. What is Schottky barrier rectifier? The Schottky diode or Schottky Barrier Rectifier is named after the German physicist “Walter H. Schottky”, is a semiconductor diode designed with a metal by the semiconductor junction. It has a low-forward voltage drop and a very rapid switching act. ... Actually, it is one of the oldest semiconductor devices in reality. 8. What is meant by Schottky effect? Schottky effect, increase in the discharge of electrons from the surface of a heated material by application of an electric field that reduces the value of the energy required for electron emission. ... The effect is named after its discoverer, the German physicist Walter Schottky. 9. Why Schottky barrier is formed? When a metal is put in direct contact with a semiconductor, a so called Schottky barrier can be formed, leading to a rectifying behavior of the electrical contact. 10. What is the barrier potential of Schottky diode? The forward voltage drop ranges from 0.3 volts to 0.5 volts. The barrier of forward voltage drop is made of silicon. The forward voltage drop is proportional to the doping concentration of N type semiconductor. Due to high concentration of current carriers, the V-I characteristic of Schottky diode is steeper.

IntroductionA p-n junction is an interface or a boundary between n-type and p-type semiconductor materials, inside a semiconductor. One of the crucial keys to solid state electronics is the nature of the P-N junction. For example, a PN Junction Diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only. And the p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons. Why pn junction exists? and How does it work? What is p-n junction diode?PN Junction IntroductionCatalogIntroductionIntroductionⅠ PN Junction Basic1.1 PN Semiconductor1.2 PN Junction ReviewⅡ PN Junction Characteristic2.1 Unidirectional Conductivity2.2 Reverse Breakdown2.3 Volt-Ampere Characteristic2.4 Capacitance CharacteristicⅢ Typical Example: Transistor PN JunctionⅠ PN Junction Basic1.1 PN SemiconductorN-type SemiconductorIn silicon crystal (or germanium crystal) doped with a small amount of impurity phosphorus element (or antimony element), since semiconductor atoms (such as silicon atoms) are replaced by impurity atoms, among the five outer electrons in the outer layer of phosphorus atoms four of them form covalent bonds with the surrounding atoms, and the extra electron is almost unbound and becomes a free electron more easily. Therefore, the N-type semiconductor has become a semiconductor with a higher concentration of electrons, and its conductivity is mainly due to the conduction of free electrons.P-type SemiconductorIn silicon crystal (or germanium crystal) doped with a small amount of impurity boron element (or indium element), since semiconductor atoms (such as silicon atoms) are replaced by impurity atoms, the three outer electrons in the outer layer of boron atoms and a semiconductor atom form a covalent bond, at this time, a "hole" is generated. This hole may attract bound electrons to "fill", making the boron atom a negatively charged ion. In this way, this type of semiconductor has a higher concentration of "holes" ("corresponding to" positive charges) and becomes a substance capable of conducting electricity.1.2 PN Junction ReviewP-N junction is formed by joining n-type and p-type semiconductor materials, which is a two terminal device that allows electric current in one direction and blocks electric current in another direction.Figure 1. How is PN Junction FormedOn a silicon wafer, different doping processes are used to form an N-type semiconductor on one side and a P-type semiconductor on the other side. We call the area near the interface of the two semiconductors a PN junction.After the P-type semiconductor and the N-type semiconductor are combined, since the free electrons in the N-type region are more and the holes are less, the concentration difference between electrons and holes appears at their junction. Due to the difference in the concentration of free electrons and holes, some electrons will diffuse from the N-type region to the P-type region, and some holes will diffuse from the P-type region to the N-type region. As a result of their diffusion, the P region loses holes, leaving negatively charged impurity ions, and the N region loses electrons, leaving positively charged impurity ions. The ions in the semiconductor cannot move arbitrarily in an open circuit, so they do not participate in conduction. These immovable charged particles form a space charge zone near the interface between the P and N zones. The thickness of the space charge zone is related to the concentration of dopants.After the space charge region is formed, due to the interaction between the positive and negative charges, an internal electric field is formed in the space charge region, the direction of which is from the positively charged N region to the negatively charged P region. Obviously, the direction of this electric field is opposite to the direction of carrier diffusion, which used to prevent diffusion.On the other hand, this electric field will cause the minority carrier holes in the N region to drift to the P region, and the minority carrier electrons in the P region to drift to the N region. The direction of the drift movement is just opposite to the diffusion movement. The holes drifting from the N region to the P region supplement the holes lost in the P region on the original interface, and the electrons drifting from the P region to the N region supplement the electrons lost in the N region on the original interface, which makes the electric charge is reduced and the internal electric field is weakened. Therefore, the result of drift motion is to narrow the space charge region and strengthen the diffusion motion.Finally, the diffusion of multiple carriers and the drift of minority carriers reach a dynamic balance. On both sides of the junction surface of the P-type semiconductor and the N-type semiconductor, a thin ion layer is left. The charge area formed by this thin ion layer is called a PN junction. The direction of the internal electric field of the PN junction points from the N to the P. It is also called the depletion layer, because lack of electrons.Figure 2. PN Junction Depletion RegionⅡ PN Junction Characteristic2.1 Unidirectional Conductivity(1) The PN junction is turned on when the forward voltage is applied.If the positive pole of the power supply is connected to the P area and the negative pole is connected to the N area, a part of the applied forward voltage is in the PN junction area, at this time, the PN junction is in a forward bias. The current flows from the P to the N, and the holes and electrons move to the interface, which narrows the space charge area. In addition, the current can pass smoothly. Its direction is opposite to the direction of the electric field in the PN junction, which weakens the internal electric field. As a result, the resistance of the internal electric field to the diffusion movement of the multitons weakens, and the diffusion current increases. The diffusion current is much larger than the drift current, and the influence of the drift current can be ignored, and the PN junction is in low resistance.(2) PN junction is cut off when reverse voltage is applied.If the positive pole of the power supply is connected to the N zone, the negative pole is connected to the P zone, and a part of the applied reverse voltage applies in the PN junction zone, and it is in reverse bias. Then the holes and electrons move away from the interface, which widens the space charge area, and the current cannot flow. The direction is the same as the direction of the electric field in the PN junction, which strengthens the internal electric field. The resistance of the internal electric field to the multiton diffusion movement is enhanced, and the diffusion current is greatly reduced. At this time, the drift current formed by the minority carriers in the PN junction region under the action of the internal electric field is greater than the diffusion current. The diffusion current can be ignored, and the PN junction exhibits high resistance.2.2 Reverse BreakdownWhen a reverse voltage is applied to the PN junction, the space charge region becomes wider and the electric field in the region strengthens. When the reverse voltage increases to a certain level, the reverse current will suddenly increase. If the external circuit cannot limit the current, the current will be so large that it will burn the PN junction. At this time, it is called the breakdown voltage. There are two basic breakdown ways, namely tunnel breakdown (also called Zener breakdown) and avalanche breakdown. The former has a breakdown voltage of less than 6V and has a negative temperature coefficient, and the latter has a breakdown voltage of greater than 6V and a positive temperature coefficient.2.3 Volt-Ampere CharacteristicThe volt-ampere characteristics of the PN junction are shown in the Figure 3, which visually shows the unidirectional conductivity.Figure 3. Volt-Ampere Curve of the PN JunctionThe volt-ampere characteristic shows by Where iD is the current passing through the PN junction, VD is the applied voltage at both ends of the PN junction, and VT is the voltage equivalent of temperature.2.4 Capacitance CharacteristicWhen a reverse voltage is applied to the PN junction, the positive and negative charges in the space charge region constitute a capacitive device. Its capacitance changes with the applied voltage, mainly including barrier capacitance (CB) and diffusion capacitance (CD). Both of them are non-linear capacitors. Ⅲ Typical Example: Transistor PN JunctionTransistors are one of the basic building blocks of modern electronics. In the diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material to form a simple pn-junction. While the transistor is a three terminal solid state device which is formed by connecting two diodes back to back. Hence it has got two PN junctions.Transistor NPN-Type and PNP-Type JunctionsTransistor Working StateThe transistor works like an electronic switch. It can turn a current ON and OFF. The basic idea behind a transistor is that it lets you control the flow of current through one channel by varying the intensity of a much smaller current that's flowing through a second channel.1) Cut-off State (C): The base current is zero.2) Amplified State (A): The transmitter junction is forward biased (that is, the voltage direction is P->N), and the collector junction is reverse biased.3) Saturation State (S): Both the emitter junction and the collector junction are forward biased.Working StateNPN-Type TransistorPNP-Type TransistorVb<Ve (C)Vc>Vb>Ve (A)Vb>Ve Vb>Vc (S)Vb>Ve (C)Vc<Vb<Ve (A)Vb<Ve Vb<Vc (S)In Figure (a), when there is no voltage input at b of the NPN transistor, no current flows between c and e, and the triode is in the cut-off state.In Figure (b), when a positive voltage is input to b of the NPN transistor, the negative electrons in the N region of e are attracted by the positrons of P region in b. Due to the effect of the power plant, and they rush (diffuse) to the base region, however, only part of the negative electrons collide with the positive electrons (recombination) to generate the base current, and the other part of the negative electrons gather near the collector junction. The negative electrons gathered in the collector junction pass through (drift) the collector junction due to the action of the electric field. After reaching the collector area, it collides with the positrons gathered in c (N-type semiconductor terminal) to generate a collector current.It can be seen from this that the greater the base current, the greater the collector current. That is, when a small current is input to the collector, a large current can be obtained by the collector, and now the transistor is in an amplified state.It should be noted that when the base current reaches a certain level, the collector current no longer rises. At this time, the transistor loses its current amplification effect, and the voltage between the collector and the emitter is very small. The collector and emitter are equivalent to the on-state of the switch. At this moment, the transistor is in a saturated state.The working principle of the PNP transistor is the same as that of the NPN transistor, except that the direction of the bias voltage and the current are opposite, and the roles of electrons and holes are reversed. The PNP transistor uses Veb to control the positrons incident on the collector area from the emitter area through the base area, while the NPN transistor uses Vbe to control the negative electrons that enter the collector area from the emitter area through the base area.In addition, in a low-power design, the transistor control circuit will have a certain impact on the circuit. No matter it is NPN or PNP, there will be leakage current in the PN junction of the transistor. When the I/O controls the base voltage, in order to stabilize the base voltage, a pull-down resistor is generally added to the base of the NPN switch circuit. In the design of the PNP switch circuit, a pull-down resistor is added to the base. The pull-up and pull-down resistors are selected according to the control chip, transistor and circuit voltage. Frequently Asked Questions about PN Junctions Formed1. What is PN junction and how it is formed?P-n junctions are formed by joining n-type and p-type semiconductor materials, as shown below. ... However, in a p-n junction, when the electrons and holes move to the other side of the junction, they leave behind exposed charges on dopant atom sites, which are fixed in the crystal lattice and are unable to move. 2. What is p-type and n-type?In silicon doping, there are two types of impurities: n-type and p-type. In n-type doping, arsenic or phosphorus is added in small quantities to the silicon. ... In p-type doping, boron or gallium is used as the dopant. These elements each have three electrons in their outer orbitals. 3. What is a PN junction diode?A PN Junction Diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only. ... By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. 4. What happens in a PN junction?A forward-biased PN junction conducts a current once the barrier voltage is overcome. The external applied potential forces majority carriers toward the junction where recombination takes place, allowing current flow. A reverse-biased PN junction conducts almost no current. 5. What is a PN junction used for?A p-n junction diode is a two terminal device that allows electric current in one direction and blocks electric current in another direction. In forward bias condition, the diode allows electric current whereas in reverse bias condition, the diode does not allow electric current.