What are the classifications of diodes by structure?

What are the classifications of diodes by structure?

There are many types of diodes, which can be divided into germanium diodes (Ge diodes) and silicon diodes (Si diodes) according to the semiconductor materials used. According to their different uses, they can be divided into detection diodes, rectifier diodes, voltage regulator diodes, switching diodes, isolation diodes, Schottky diodes, light-emitting diodes, silicon power switch diodes, rotating diodes, etc. According to the chip structure, it can be divided into point contact diodes, surface contact diodes, and planar diodes. A point contact diode is made by pressing a very thin metal wire onto a smooth semiconductor chip surface, applying a pulse current to firmly sinter one end of the wire with the chip, forming a "PN junction". Due to its point contact, only small currents (not exceeding tens of milliamps) are allowed to pass through, making it suitable for high-frequency low current circuits such as radio detectors. The "PN junction" area of surface contact diodes is relatively large, allowing for larger currents (several amps to tens of amps) to pass through. They are mainly used in "rectification" circuits that convert alternating current into direct current. A planar diode is a specially designed silicon diode that can not only pass large currents, but also has stable and reliable performance. It is commonly used in switching, pulse, and high-frequency circuits.

1、 Classification based on construction

Semiconductor diodes mainly operate by relying on PN junctions. The point contact type and Schottky type, which are inseparable from the PN junction, are also included in the scope of general diodes. Including these two models, based on the characteristics of PN structure surface construction, crystal diodes are classified as follows:

1. Point contact diode

Point contact diodes are formed by pressing a metal needle onto a single crystal of germanium or silicon material and then using the current method. Therefore, its PN junction has a small electrostatic capacity and is suitable for high-frequency circuits. However, compared to surface junction diodes, point contact diodes have poor forward and reverse characteristics, and therefore cannot be used for high currents and rectification. Due to its simple structure, it is inexpensive. For general applications such as detection, rectification, modulation, mixing, and limiting of small signals, it is a widely used type.

2. Key type diode

A key type diode is formed by fusing or silver filaments onto a single crystal of germanium or silicon. Its characteristics are between point contact diodes and alloy diodes. Compared with point contact type, although the PN junction capacity of key type diodes has slightly increased, their forward characteristics are particularly excellent. Commonly used as a switch, sometimes also applied to detection and power rectification (not greater than 50mA). In key type diodes, diodes with fused gold wires are sometimes referred to as gold bond type, while diodes with fused silver wires are sometimes referred to as silver bond type.

3. Alloy type diode

A PN junction is formed on a single crystal wafer of N-type germanium or silicon by alloying with metals such as indium and aluminum. Small forward voltage drop, suitable for high current rectification. Due to its high static capacitance when the PN junction is reversed, it is not suitable for high-frequency detection and rectification.

4. Diffusion diode

Heating a single crystal of N-type germanium or silicon in a high-temperature P-type impurity gas causes a portion of the surface of the single crystal to become P-type, thus forming a PN junction. Due to the small forward voltage drop of PN junction, it is suitable for high current rectification. Recently, the mainstream use of high current rectifiers has shifted from silicon alloy type to silicon diffusion type.

5. Desktop diode

The production method of PN junction is the same as that of diffusion type, but only the PN junction and its necessary parts are retained, and the unnecessary parts are corroded away with drugs. The remaining part takes on a rectangular shape, hence the name. The initial production of the tabletop was made using diffusion method on semiconductor materials. Therefore, this type of tabletop is also called a diffusion tabletop. For this type, it seems that there are few product models used for high current rectification, while there are many product models used for low current switches.

6. Planar diode

A PN junction formed by selectively diffusing only a portion of P-type impurities on a semiconductor single crystal wafer (mainly N-type silicon single crystal wafer) and utilizing the shielding effect of the silicon wafer surface oxide film. Therefore, there is no need to adjust the PN junction area for drug corrosion. Due to the flatness of the semiconductor surface, it is named. Moreover, the surface of PN bonding is recognized as a type with good stability and long lifespan due to being covered by an oxide film. Initially, the semiconductor materials used were formed using epitaxial methods, hence the planar type was also referred to as epitaxial planar type. For planar diodes, there seem to be few models used for high current rectification, while there are many models used for low current switching.

7. Schottky diode

The basic principle is to use the formed Schottky barrier on the contact surface between metal (such as lead) and semiconductor (N-type silicon wafer) to block reverse voltage. The rectification principles of Schottky and PN junctions have fundamental differences. Its voltage resistance is only about 40V. Its strengths are: very fast switching speed and particularly short reverse recovery time trr. Therefore, it is possible to produce switch diodes and low-voltage high current rectifier diodes.