What Is an Avalanche Transistor?

Avalanche diodes are solid-state microwave devices that generate negative resistance by using the physical effects of collision ionization and transit time of carriers in semiconductor structures.

Avalanche diode

In a PN junction with a low material doping concentration, as the reverse voltage of the PN junction increases, the electric field in the space charge region increases. In this way, the electrons and holes passing through the space charge region will increase the energy obtained under the action of the electric field, and the electrons and holes moving in the crystal will continuously collide with the crystal atoms again. When it is large enough, the electrons in the covalent bond can be excited to form a free electron-hole pair by such a collision. The newly generated electrons and holes also move in the opposite direction, regaining energy, and can again generate electron-hole pairs through collision. This is the carrier multiplication effect. When the reverse voltage is increased to a certain value, the carrier multiplication is like an avalanche on a steep snow-covered mountain slope. An avalanche breakdown occurred. This feature can be used to make high-reverse-voltage diodes. The following figure is a schematic diagram of avalanche breakdown.

The avalanche diode is a negative resistance device, which is characterized by high output power but high noise. The main noise comes from avalanche noise, which is caused by the generation of electrons and holes and irregularities during the avalanche multiplication process, and its properties are similar to shot noise. Avalanche noise is the main reason why the noise of avalanche diode oscillators is much higher than other oscillators

Avalanche diodes (7 photos)