Commonly used semiconductor devices - crystal triode study notes

【Structure and symbol of crystal triode】

1] Transistor structure

1) Emission region: The emission region has a high doping concentration and is used to emit free electrons

2) Base region: The base region is very thin and has a very low impurity concentration. Part of the free electrons diffused from the emitter region will be neutralized by the holes in the base region.

3) Collector region: The area is very large. After the free electrons pass through the base region, the remaining free electrons will reach the collector region due to drift motion.

2】Transistor symbol

【Current amplification function of transistor】

1] Movement of carriers inside transistors

1) The VCC voltage is greater than VBB, making the emitter junction forward biased and the collector junction reverse biased (the collector junction is on the top)

2) A forward voltage is applied to the emitter junction, and the diffusion movement forms the emitter current IE. Note that the impurity concentration in the emitter region is high, so many free electrons diffuse out.

3) The free electrons diffused to the base region and the combined movement of holes form the base current IB. Due to the action of the power supply VBB, the combined movement continues

4) A reverse voltage is applied to the collector junction, and the drift motion forms the collector current IC. Note that although the amount of free electrons is large, since the base region is P-type, the free electrons are still minority electrons in the base region.

5) Other currents are relatively small and can be ignored

2】Current distribution relationship of transistor

It is easy to see from the figure that the following current relationship

IE = IEN + IEP = ICN + IBN + IEP

IC = ICN + ICBO

IB = IBN + IEP - ICBO

From the outside: IE = IC + IB

3】Transistor amplification factor

[Common-emitter characteristic curve of transistor]

This circuit is called the basic common emitter amplifier circuit

1】Input characteristic curve

Input characteristic curve description: The functional relationship between base current IB and emitter junction voltage drop UBE when voltage drop UCE is constant

1) When UCE = 0, it is equivalent to the collector and emitter being short-circuited. Therefore, the input characteristic curve is similar to the PN junction volt-ampere characteristic.

2) A part of the unbalanced minority carriers (free electrons) injected from the emitter region into the base region crosses the base region and the collector junction to form the collector current IC, causing the unbalanced minority carriers participating in the recombination motion in the base region to follow

UCE increases and decreases. To obtain the same IB, UBE should be increased, so the UE increase curve shifts to the right.

3) When UCE increases to a certain value, the electric field of the collector junction is strong enough to collect most of the non-equilibrium minority carriers injected into the base region from the emitter region into the collector region. Therefore, if UCE is further increased,

IC is not significantly increased.

2】Output characteristic curve

Output characteristic curve description: When the base current IB is a constant, the functional relationship between the collector current IC and the tube voltage drop UCE

1) When UCE increases from zero, the collector junction electric field increases, the ability to collect non-equilibrium minority carriers in the base region increases, and IC increases.

2) When UCE increases to a certain value, the collector junction electric field is sufficient to collect most of the non-equilibrium minority carriers in the base region. When UCE increases further, the IC geometry remains unchanged.

3) Cut-off region: The emitter junction voltage is less than the turn-on voltage UON, and the collector junction is reverse biased, i.e., UCE > UBE

4) Amplification region: the emitter junction is forward biased and the collector junction is reverse biased, that is, UBE > UON and UCE >= UBE

5) Saturation region: Both the emitter junction and the collector junction are forward biased, that is, UBE > UON, and UBE > UCE

6) Saturation phenomenon: When UBE increases, IB increases accordingly, but IC does not increase much or remains basically unchanged

【Main parameters of transistor】