Patch diodes are very common electronic products, semiconductor diodes mainly rely on PN junctions and work. And PN junctions are inseparable point contact type and Schottky type, also included in the scope of the general diode. Including these two models, according to the characteristics of PN junction surface, the crystal diodes are classified as follows:
According to structural classification
 
⒈ point contact type diode
The point-contact diode is formed by pressing a metal needle on a single wafer of germanium or silicon material and then by a current method. Therefore, the PN junction of the electrostatic capacity is small, suitable for high-frequency circuit. However, compared with the surface junction type, point contact type diode positive and reverse characteristics are poor, therefore, can not be used for high current and rectifier. Because the structure is simple, so cheap. For small-signal detection, rectification, modulation, mixing and limiting and other general purposes, it is a wider range of applications.
⒉ key type diode
A key type diode is formed by fusing a gold or silver filament on a single wafer of germanium or silicon. Its characteristics are between point-contact diodes and alloy diodes. Compared with the point contact type, although the PN junction capacitance of the key type diode is slightly increased,
 
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Positive characteristics are particularly good. Multi-switch, and sometimes used in detection and power supply rectification (not more than 50mA). In the key-type diode, the welding of gold wire diodes are sometimes referred to as gold-type, welded wire diodes are sometimes referred to as silver-type.
⒊ alloy type diode
In the N-type germanium or silicon single-chip, through the alloy indium, aluminum and other metal method of making PN junction formed. The forward voltage is reduced and is suitable for high current rectification. Because of its PN junction reverse when the electrostatic capacity, it is not suitable for high frequency detection and high frequency rectifier.
⒋ diffusion type diode
In the high-temperature P-type impurity gas, the N-type germanium or silicon single crystal is heated so that a part of the surface of the single crystal becomes P-type, and the PN junction is made. Due to PN junction forward voltage decreases, suitable for high current rectifier. Recently, the mainstream of using high current rectifiers has been shifted from silicon alloy to silicon diffusion.
⒌ countertop diode
The method of making the PN junction is the same as that of the diffusion type, but only the PN junction and its necessary part are retained, and the unnecessary part is corroded with the drug. The rest of the part will show a table shape, hence the name. The initial production of the countertop type, is the use of semiconductor materials diffusion method made of. Therefore, this kind of table-like type is called diffusion table type. For this type, it seems that high current rectification with the product model is very small, and small current switch with a lot of product models.
⒍ flat diodes
A PN junction is formed by selectively diffusing a part of the N-type silicon single wafer by diffusion of the P-type impurity on the semiconductor single crystal wafer (mainly the N-type silicon single wafer) by the shielding effect of the surface oxide film of the silicon wafer. Therefore, there is no need to adjust the PN junction area of the drug corrosion. As the semiconductor surface was made flat, hence the name. In addition, since the PN-bonded surface is covered with an oxide film, it is recognized as having a good stability and a long life type. Initially, the semiconductor material used is formed by the epitaxial method, so the plane is called the epitaxial plane type. For planar diodes, it seems that the type used for high current rectification is very small, and for small current switch with a lot of models.
⒎ alloy diffusion type diode
It is a kind of alloy. The alloy material is a material that is easily diffused. The hard-to-fabricate material can be blended with the alloy by cleverly blending the impurities so that an appropriate concentration distribution of the impurities is obtained in the PN junction that has been formed. This method is suitable for manufacturing high sensitivity varactor diodes.
⒏ epitaxial diodes
A diode is formed by making a PN junction with a process with a long extension. Manufacturing requires very high technology. It is possible to arbitrarily control the distribution of different concentrations of impurities, so that it is suitable for manufacturing highly variable varactor diodes.
 
According to use classification
 
⒈ detection with diodes
In principle, the removal of the modulation signal from the input signal is detected by the size of the rectified current (100mA) as the boundary of the output current is usually less than 100mA called detection. Germanium material point contact type, the working frequency up to 400MHz, the forward pressure drop is small, the junction capacitance is small, the detection efficiency is high, the frequency characteristic is good, is 2AP type. Similar to the touch type as the detection of the diode, in addition to
 
General diodes
Detection, but also for limiting, clipping, modulation, mixing, switching and other circuits. There are also two diode assemblies with good characteristics for FM detection.
⒉ rectifier diode
Rectifier diode internal structure for a PN junction, the shape of the package with metal shell, plastic packaging and glass packaging and other forms. The size of the tube varies with the parameters of the rectifier. Rectifier diode is mainly used for rectifier circuit, the use of single conductivity of the diode, the AC into DC. As the rectifier tube forward current is large, so the rectifier diode for the surface contact type of the diode, junction area, junction capacitance, but the operating frequency is low. 2CP series of shell for small current rectifier.
Rectangular current
Refers to the rectifier diode for a long time to work through the current value.
⑵ reverse operating voltage
It refers to the rectifier diode at both ends of the reverse voltage can not exceed the specified voltage allowed value. If this exceeds the allowable value, the rectifier may breakdown.