Q.What do you mean by Doping ?

Doping is the deliberate, controlled addition of a suitable impurity to an intrinsic semiconductor to increase its conductivity by creating an excess of either free electrons or holes.

1. A pure (intrinsic) semiconductor such as silicon or germanium has a very small number of charge carriers at room temperature, so its conductivity is low.
2. To make it useful for devices, a small, precisely controlled quantity of a suitable impurity atom is deliberately added to the pure semiconductor crystal during crystal growth — this process is called doping.
3. Adding a pentavalent impurity (e.g. Phosphorus, Arsenic — 5 valence electrons) donates an extra free electron per atom, producing an n-type semiconductor (electrons as majority carriers).
4. Adding a trivalent impurity (e.g. Boron, Indium — 3 valence electrons) creates a hole (electron deficiency) per atom, producing a p-type semiconductor (holes as majority carriers). …