What is Acceptor Impurity

An acceptor impurity is a physical material which, when added to a semiconductor, can form a P-type region by creating positive charges or holes in semiconductor materials such as silicon or germanium.

When a small quantity of impurity is added to a semiconductor to contribute either free electrons or holes in this way, it changes the semiconductor’s conducting properties. This process is known as doping the semiconductor.

If a trivalent impurity – i.e. an impurity containing atoms with three valence electrons - is added to an intrinsic semiconductor, then excess holes will be created in the crystal. This is because when a trivalent impurity is added to the semiconductor crystal, the trivalent atoms will replace some of the tetravalent semiconductor atoms. The three valance electrons of a trivalent impurity atom will bond with three neighbouring semiconductor atoms. Hence, there will be a lack of an electron in one bond of the fourth neighbouring semiconductor atom which contributes a hole to the crystal.

Since trivalent impurities contribute excess holes to semiconductor crystal, and these holes can accept electrons, these impurities are referred as acceptor impurities. As the holes virtually carry positive charge, the said impurities are referred as positive - type or p type impurities and the semiconductor with p type impurities is called a p type semiconductor.