Amplification of the transistor

Carrier transmission in triodes Process: For details, please see: Semiconductor triode ppt document.

1. Carrier transport process
(1) Emission.
(2) Diffusion and recombination.
(3) Collection.

2. Current distribution

Transistor current distribution diagram

The collector current IC consists of two parts: ICn and ICBO. The former is formed by the electrons emitted by the emitter region being collected by the collector, and the latter is formed by the drift motion of minority carriers in the collector region and the base region, which is called the reverse saturation current. So
?? IC＝ICn＋ICBO (2 - 1)

The emitter current IE also consists of two parts: IEn and IEp. IEn is the current formed by the electrons emitted by the emitter region, and IEp is the current formed by the holes diffused from the base region to the emitter region. Because the emitter region is heavily doped, IEp is negligible, that is, IE≈IEn. IEn is divided into two parts, the main part is ICn, and a very small part is IBn. IBn is the current formed when electrons recombine with holes in the base region. The holes in the base region are provided by the power supply UBB, so it is part of the base current. ?

The base current IB is the difference between IBn and ICBO:

Most of the electrons injected into the emitter region can reach the collector and form a collector current, which requires ICn>>IBn.
The above relationship is usually measured by the common base DC current amplification factor, which is expressed as α and is defined as

The α value of a general triode is 0.97 to 0.99. Substituting (2-4) into (2-1), we can get: