What parameters of BJT will change when the temperature changes? How to change

The change of temperature will cause the change of BJT band gap width and minority carrier concentration. Forward voltage drop decreases with the increase of temperature, reverse current increases rapidly with the increase of temperature, and barrier capacitance increases with the increase of temperature.

Because BJT is made of semiconductor, and the semiconductor here has two parameters related to temperature: one is band gap (generally decreasing with the increase of temperature); The second is the minority carrier concentration (increasing exponentially with the temperature).

Extended data:

Classification of BJT:

1, NPN type:

NPN transistor is one of two types of bipolar transistors, which consists of two N-doped regions and a P-doped semiconductor (base) between them. The small current input to the base will be amplified, resulting in a large collector-emitter current. When the base voltage of the NPN transistor is higher than the emitter voltage and the collector voltage is higher than the base voltage.

The transistor is in a forward amplification state. In this state, there is a current between the collector and emitter of the transistor. The amplified current is the result of electrons injected from the emitter into the base region (minority carriers in the base region) drifting to the collector under the push of the electric field. Because electron mobility is higher than hole mobility, most bipolar transistors used now are NPN type.

2.PNP type:

Another type of bipolar transistor is PNP, which consists of two layers of P-doped regions and a layer of N-doped semiconductor between them. The tiny current flowing through the base can be amplified at the emitter. That is, when the base voltage of PNP transistor is lower than the emitter, the collector voltage is lower than the base, and the transistor is in the forward amplification region.

In the electrical symbol of bipolar transistor, the arrow between the base and emitter points to the direction of current, where the current is the opposite direction of electron flow. Contrary to NPN type, the arrow of PNP type transistor points from emitter to base.

3. Heterojunction bipolar transistor: It is an improved bipolar transistor with the ability of high-speed operation. It is found that this transistor can handle ultra-high frequency signals with frequency as high as several hundred GHz, so it is suitable for RF power amplification, laser driving and other applications that require strict working speed.

Heterojunction is a kind of PN junction, and both ends of this junction are made of different semiconductor materials. In this bipolar transistor, the emitter junction usually adopts heterojunction structure, that is, the emitter region adopts wide band gap material and the base region adopts narrow band gap material. The common heterojunction uses gallium arsenide (GaAs) as the base region and Al-Ga-As solid solution (AlxGa 1-xAs) as the emitter region.

With such heterojunction, the injection efficiency of bipolar transistor can be improved, and the current gain can also be improved by several orders of magnitude.

Baidu encyclopedia-bipolar transistor