Transistor Construction

A transistor is constructed by placing a oppositely doped semiconductor material between two similarly doped semiconductors. Or placing n-type material between two p-type material which forms the pnp-transistor or by placing a p-type material between two n-type semiconductor which forms npn-transistor.



The above diagram shows the schematic construction of a PNP transistor. As you can see an N-type silicon (green layer) is sanwidged between two P type materials (red layer). The left part is indicated by P+ which means its highly doped P-type material. This highly doped portion is called Emitter, that is its the piece of semiconductor that supplies majority carriers for the transistor to function. At the extreme right is moderately doped P type material which is called as the Collector. This portion collects the majority charge carriers that is been emitted by Emitter and that manage to cross the collector. The middle region is denoted by n- because its doped with N-type impurities. The minus'-' sign indicates its doped very very less compared to the emitter and collector. The middle region is called the Base, and its this region that serves as a gate, regulating flow of charge from Emitter to collector.

The doping of base is just one tenth of that of collector. In a real transistor, the width of base is very thin. The total width od the transistor will be 150 times that of the width of the base.