Engineering Physics

8.5 Carrier concentration in extrinsic semiconductors

The number of charge carriers present per unit volume of a semiconductor material is called carrier concentration. Suppose donor and acceptor atoms are doped in a semiconductor, then at some room temperature T K, the material contains n, p, N⁻_A and N⁺_D, which denote number of conduction electrons, holes, acceptor ions and donor ions per unit volume of material, respectively. The material will be electrically neutral if,

n + N⁻_A = p + N⁺_D _________ (8.54)

That is the total negative charge due to conduction electrons and acceptor ions is equal to holes and donor ions in unit volume of material. Equation (8.54) is called charge neutrality equation. In the above equation,

And the product of acceptor ...