p-type semiconductor: Consider a trivalent impurity such as Gallium (Ga, Z = 31) is doped in a pure semiconductor germanium (Ge, Z = 32).
Each Ga atom forms three covalent bonds with three germanium atoms as shown in the figure. In the fourth covalent bond, only Ge atom contributes one valence electron, while Ga has no electron to contribute. Thus, the fourth bond is incomplete, being short of one electron. This missing electron is called a ‘hole'. Ga atom is ready to accept one electron and hence all such trivalent impurities are called acceptors. A small amount of Ga provides millions of holes which are more in number than electrons available for conduction.The resulting semiconductor is called a p-type semiconductor. A p-type semiconductor is formed when a small quantity of acceptor impurity is added to the pure semiconductor.In a p-type semiconductor, conduction is mainly by means of holes in the valence band. Hence holes are majority carriers and electrons are minority carriers in a p- type semiconductor.