How a PN junction forms?

One of the keys to solid state electronics is the nature of the P-N junction.

To understand how a pn-junction works, begin by imagining two separate bits of semiconductor, one n-type, the other p-type

Semiconductors p and n type

Semiconductors p and n type are joined together

Electrons and Holes migrate across the pn junction as we can see below.

Depletion Region is formed

A potential difference is set up across the depletion region or depletion layer.