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What is Transistor and its types - Physics, Electronics - eSaral

A Transistor is an electronic device formed by P and N types of semiconductors. If you want to know about what is transistor and its types then read this article till the end.


  • Transistor is used in place of triode valve, it is an electronic device formed by P and N types of semiconductors. It was discovered by American scientist J Barden, W.H. Bratain, W. Shockley.
  • The transistor is three-terminal and two P-N Jn. device.

There are two types of transistors

  1. N-P-N transistor
  2. P-N-P transistor
What is Transistor and its types
What is Transistor and its types
A transistor (P-N-P or N-P-N) has the following sections:

Emitter: It emits the charge carriers and it is heavily doped.

Base: The middle section of the transistor is known as the base. This is very lightly doped and very thin ($10^{-6}$ m).

Collector: This is moderately doped. It collects the charge carriers

Important points
  • The cross-sectional area of the base is very large as compared to the emitter.
  • The cross-sectional area of the collector is less than the base but greater than the emitter.
  • The base is much thinner than the emitter while the collector is wider than both because the emitter emits charge carriers and the collector has to receive a maximum of them. Since the base is very thin, so recombination in the base region is very less maximum 5%.
  • The emitter is heavily doped so that it can provide a large number of charge carriers (electrons or holes) into the base. The base is lightly doped and is very thin, hence the majority of charge carriers move on to the collector. This lower doping decreases the conductivity (increases the resistance) of the base material by limiting the number of charge carriers to the collector. The collector is moderately doped.
  • The emitter is always connected in forward biased and the collector is always connected in reverse biased.
  • The resistance of the emitter-base junction (forward-biased) is very small as compared to a collector-base junction (reverse biased). Therefore, the forward bias applied to the emitter base is generally very small whereas reverse bias on the collector base is much higher.
  • Arrowhead always shows the emitter's current direction.
  • Current conduction within the P-N-P transistor takes place by hole conduction from emitter to collector.
  • Conduction in the external circuit is carried out by electrons.

So, that's all from this blog. I hope you get the idea about what is transistors and its types. If you have any confusion related to this topic then feel free to ask in the comments section down below.

Also, read
Different types of PN-junction diodes

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