When a p- type semiconductor is suitably joined to an n-type semiconductor the contact surface so formed is called p-n junction.
When a p- type semiconductor is suitably joined to an n-type semiconductor the contact surface so formed is called p-n junction. All
the semiconductor devices contain one or more p-n junction. P-N junction is
fabricated by special techniques namely growing, alloying and diffusion
methods. The p-type semiconductor is having egative acceptor ions and positively charged electrons. The n-type semiconductor
is having positive donor ions and negatively charged electrons. When the two
pieces are joined together
and suitably treated they form a p-n junction. The moment they form a p-n
junction, some of the conduction electrons from n-type material diffuse over to
the p- type material and undergo electron - hole recombination with the holes
available in the valence band. Simultaneously holes from p-type material
diffuse over to n- type material and undergo hole-electron combination with the
electrons available in the conduction band. This process is called diffusion.
When a p-n junction is connected across an electric supply, the junction is
said to be under biasing. The potential difference across the p- n junction can
be applied in two ways, namely- forward biasing and reverse biasing. When the positive
terminal of a dc source is connected to p-type, and negative terminal is
connected n-type semiconductor of a p-n junction, the junction is said to be in
forward biasing. When the positive terminal of a dc source is connected to
n-type, and negative terminal is connected p-type semiconductor of a p-n
junction, the junction is said to be in reverse biasing. With forward bias, a
low resistance path is set up in the p-n junction, and hence current flows
through the circuit. With reverse bias, a high resistance path is set up and no
current flows through the circuit. This property is best suited for
rectification of ac into dc.
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: P - N junction |