Classification of common crystal diodes

1. Classification according to structure

　　Semiconductor diodes mainly rely on PN junctions to work. The point contact type and Schottky type, which are inseparable from the PN junction, are also included in the range of general diodes. Including these two models, according to the characteristics of the PN structure, the crystal diodes are classified as follows:

1. Schottky diode

　　 The basic principle is: on the contact surface of metal (such as lead) and semiconductor (N-type silicon wafer), the formed Schottky is used to block the reverse voltage. There is a fundamental difference between the rectification principle of Schottky and PN junction. Its withstand voltage is only about 40V. Its specialty is: the switching speed is very fast: the reverse recovery time trr is particularly short. Therefore, switching diodes and low-voltage high-current rectifier diodes can be fabricated.

2. Planar diode

"On semiconductor wafers (mainly N-type silicon wafers), P-type impurities are diffused, and the PN junction formed by selectively diffusing a part of the N-type silicon wafer by using the shielding effect of the oxide film on the surface of the silicon wafer. Therefore, there is no need to adjust the corrosion effect of chemicals for the area of the PN junction. It is named because the surface of the semiconductor is made flat. In addition, the PN-bonded surface is covered by an oxide film, so it is recognized as a type with good stability and long life. Initially, the semiconductor materials used were formed by epitaxial methods, so the planar type was also called the epitaxial planar type. For planar diodes, it seems that there are few models used for high-current rectification, while many models are used for low-current switching.

3. Diffusion diode

　　In the high-temperature P-type impurity gas, heating the single chip of N-type germanium or silicon to make a part of the surface of the single chip become P-type, in this way PN junction. Due to the small forward voltage drop of the PN junction, it is suitable for large current rectification. Recently, the mainstream of using high-current rectifiers has shifted from the silicon alloy type to the silicon diffusion type.

2. Classification according to purpose

1. Zener diode

　　 is a product that replaces the Zener electronic diode. It is made into a diffusion type or alloy type of silicon. It is a diode whose reverse breakdown characteristic curve changes rapidly. It is made for use as control voltage and standard voltage. The terminal voltage (also known as Zener voltage) of the diode when it is working ranges from about 3V to 150V, and can be divided into many levels at every 10%. In terms of power, there are also products from 200mW to more than 100W. Working in the reverse breakdown state, made of silicon material, the dynamic resistance RZ is small, generally 2CW type; if two complementary diodes are connected in reverse series to reduce the temperature coefficient, it is 2DW type.

2. Schottky Barrier Diode (Schottky Barrier Diode)

　　 It is a "metal semiconductor junction" diode with Schottky characteristics. Its forward starting voltage is low. In addition to materials, the metal layer can also be made of gold, molybdenum, nickel, titanium and other materials. Its semiconductor materials are silicon or gallium arsenide, mostly N-type semiconductors. This kind of device is conducted by majority carriers, so its reverse saturation current is much larger than that of a PN junction conducted by minority carriers. Because the storage effect of the minority carriers in the Schottky diode is very small, its frequency response is only limited by the RC time constant. Therefore, it is an ideal device for high-frequency and fast switching. Its working frequency can reach 100gHz. In addition, MIS (metal-insulator-semiconductor) Schottky diodes can be used to make solar cells or light-emitting diodes.

3. Light-emitting diodes

　　 is made of gallium phosphide and gallium arsenide phosphorous materials, small in size, and forward driving to emit light. The working voltage is low, the working current is small, the light is uniform, the life is long, and it can emit red, yellow and green monochromatic light.

3. Classification according to characteristics

Point contact diodes are classified as follows according to the forward and reverse characteristics.

1. Generally use point contact diodes

This kind of diode, as the title says, is usually used in detection and rectification circuits. It is an intermediate product whose forward and reverse characteristics are neither particularly good nor particularly bad. Such as: SD34, SD46, 1N34A, etc. belong to this category.

2. High reverse withstand voltage point contact diode

　　 is a product with high maximum peak reverse voltage and maximum DC reverse voltage. Used for detection and rectification of high-voltage circuits. The forward characteristics of this type of diode are generally not good or fair. Among the point contact type germanium diodes, there are SD38, 1N38A, OA81 and so on. This kind of germanium material diode, its withstand voltage is limited. Silicon alloy and diffusion type are available for higher requirements.

3. Point contact diode with high reverse resistance

　　The forward voltage characteristics are the same as those of general diodes. Although its reverse withstand voltage is also particularly high, but the reverse current is small, so its specialty is high reverse resistance. Used in high input resistance circuits and high resistance load resistance circuits, as far as germanium material high reverse resistance diodes are concerned, SD54, 1N54A, etc. belong to this type of diode.

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