Brief introduction of bipolar transistor

Bipolar transistor (BJT), commonly known as triode, is an electronic device with three terminals. Bipolar transistor is a revolutionary invention in the history of electronic education. Its inventors william shockley, john bardeen and walter brattain were awarded the 1956 Nobel Prize in Physics. The work of this transistor involves the flow of electrons and holes, so it is called bipolar, so it is also called bipolar carrier transistor. This working mode is different from unipolar transistors such as field effect transistors, and it only involves the drift of a single type of carriers. The boundary between two different dopant accumulation regions is formed by a PN junction. Bipolar transistor consists of three parts of semiconductors with different doping levels. The charge flow in the transistor is mainly due to the diffusion and drift motion of carriers at the PN junction. Take NPN transistor as an example. According to this design, electrons in the highly doped emitter region move to the base by diffusion. In the base region, holes are majority carriers and electrons are minority carriers. Because the base region is very thin, these electrons reach the collector through drift motion, thus forming collector current, so bipolar transistors are classified as minority carrier devices. Bipolar transistors can amplify signals and have good power control, high-speed operation and durability, so they are often used to form amplification circuits or drive speakers, motors and other equipment, and are widely used in aerospace engineering, medical instruments and robots.