Extrinsic semiconductors: A doped semiconductor or a sein iconductor with impurity atoms is called an extrinsic semiconductor.
p-Type semiconductors
In p-type Ge. If we dope intrinsic Ge, with a controlled amount of trivalent atoms, say indium (In or boron B or aluminium Al) Group III, which has three valence electrons, impurity atom will occupy places of some Ge atoms and there will be one incomplete covalent bond with a neighbouring Ge atom, due to the deficiency of an electron. This is completed by taking an electron from one of the Ge-Ge bonds, thus completing the In-Ge bond.
This makes In ionized (negatively charged), and creates a ‘hole’ or an electron deficiency in Ge. The trivalent atoms are called acceptor atoms and this extrinsic semiconductor is known as p-type.
