Structure and types of transistor

Crystal transistor is one of the basic semiconductor components, which has the function of current amplification and is the core component of electronic circuits. A transistor is made by fabricating two PN junctions that are very close to each other on a semiconductor substrate. The two PN junctions divide the positive block semiconductor into three parts, with the middle part being the base region and the two sides being the emitter and collector regions. There are two arrangements: PNP and NPN. As shown in the figure, corresponding electrodes are drawn from the three regions, namely the base b, emitter e, and collector c.transistor

The PN junction between the emitter region and the base region is called the emitter junction, and the PN junction between the collector region and the base region is called the collector junction. The base region is very thin, while the emitter region is thick with high impurity concentration. The PNP transistor emitter region "emits" holes, which move in the same direction as the current direction, so the emitter arrow points inward; The emitter region of an NPN transistor emits free electrons, which move in the opposite direction to the current direction, so the emitter arrow is pointing outward. The emitter arrow is pointing outward. The direction of the emitter arrow is also the conduction direction of the PN junction under forward voltage. Both silicon transistor and germanium transistor have two types: PNP and NPN.transistor