Question

explain PN junction? with diagram?

Answer 1

 A p-n junction consists of two semiconductor regions with opposite doping type as shown in Figure 4.2.1. The region on the left is p-type with an acceptor density Na, while the region on the right is n-type with a donor density Nd. The dopants are assumed to be shallow, so that the electron (hole) density in the n-type (p-type) region is approximately equal to the donor (acceptor) density.
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Answer 2

the device formed by joining atomically a wafer of P- type semiconductor to the N - type semiconductor is known as P - N junction.

there are three process of making junctions,
diffusion
alloying
growth

diffusion - the impurity concentration is maximum at surface and decreases gradually inside the semiconductor