Question

Draw the energy band diagrams of (i) n-type and (ii) p-type semiconductor at temperature, T > OK

In the case n-type semiconductor, the donor energy level is slightly below the bottom of the conduction band whereas in the p-type semiconductor, the acceptor energy level is slightly above the top of the valence band.

Explain, what role do these energy levels play in conduction and valence bands.

Answer 1

For a n-type semiconductor. 

The electrons, from the donor impurity atoms, can move into the conduction band with very small supply of energy. The conduction band, therefore, has electrons as the majority charge carriers.

For a p-type semiconductor 

In these semiconductors, a very small supply of energy can cause an electron from its valence band to jump to the acceptor energy level. The valence band, therefore, has a dominant density of holes in it. This effectively implies that the holes are the majority charge carriers in p-type semiconductor.