Question

What is a transistor? Distinguish between p-n-p and n-p-n transistor.

Answer 1

Transistor is a 3-Terminal semiconductor device. In a junction transistor, there are 2 types of charge carriers (i.e. holes and electrons, so it is known as Bipolar junction transistor).

A junction transistor consists of a thin layer of one type of extrinsic semiconductor sandwiched between two thick layers of other types of extrinsic semiconductor.

The three layers in transistors are:

1. $Emitter$: One side of a transistor which is of moderate size but heavily doped is known as an emitter. Its function is to supply majority charge carriers to the base region.
   
2. $Base$: The middle region of a transistor which is very thin and lightly doped us called Base.
3. $Collector$: The other side of Transistor which is doped slightly less than the emitter but having thickness slightly more than that of the emitter is called the collector. The junction of the collector is to gather the majority charge carriers sent by the emitter.

There are two types of transistors:

$npntransistor$	$pnptransistor$
1. When a thin layer of p-type semiconductor is sandwich between two thick layers of the n-type of the semiconductor. npn transistor is formed	1. When n-type semiconductor is sandwich between two thick layers of the p-type of the semiconductor.pnp transistor is formed.
2. Electrons are the majority charge carriers.	2. Holes are the majority charge carriers.

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