P-Type Semiconductors – revision notes

P-type semiconductors are obtained by adding trivalent impurities (Boron, Gallium, Indium, Aluminum) to a pure semiconductor. The three valence electrons of the impurity atom form covalent bonds with neighboring semiconductor atoms and the fourth covalent bond has a vacancy. This gives rise to a hole in the semiconductor.

Thus the addition of trivalent impurity atom creates holes in the semiconductor. The trivalent impurities which produce P-type semiconductors are known as acceptor impurities because the holes created can accept the electrons.

In a P-type semiconductor, a large number of free holes are created by doping which improves its conductivity. However, there will be a very small amount of free electrons created because of thermal agitation.

Free holes are much more in number and so they can be termed as majority carriers. And free electrons are comparatively less in number, hence they can be termed as the minority carriers.

Therefore in P-type semiconductors, holes are the majority charge carriers and electrons are the minority charge carriers.