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A p-type semiconductor is a type of semiconductor. When the trivalent impurity is added to an intrinsic or pure semiconductor (silicon or germanium), it is said to be a p-type semiconductor. Trivalent impurities such as boron (B), gallium (Ga), indium (In), aluminium (Al) etc. are called acceptor impurity. Ordinary semiconductors are made of materials that do not conduct (or carry) an electric current very well but are not highly resistant to doing so. They fall half way between conductors and insulators. An electric current occurs when electrons move through a material. In order to move, there must be an electron 'hole' in the material for the electron to move into. A p-type semiconductor has more holes than electrons. This allows the current to flow along the material from hole to hole but only in one direction.
Semiconductors are most often made from silicon. Silicon is an element with four electrons in its outer shell. To make a p-type semiconductor extra materials like boron or aluminium are added to the silicon. These materials have only three electrons in their outer shell. When the extra material replaces some of the silicon it leaves a 'hole' where the fourth electron would have been if the semiconductor was pure silicon.
P-type semiconductors are made by doping the pure semiconductor material. The amount of impurity added is very small compared to the amount of semiconductor. The exact character of the semiconductor can be changed by varying the amount of 'dopant' that is added. In p-type semiconductors the number of holes is much higher than that of thermally generated electrons.