P-type semiconductor

The extrinsic p Type Semiconductor is formed, when a trivalent impurity is added to a pure silicon or germanium atom in small amount and as result large number of holes are created in it.

A trivalent impurity like boron, aluminium, nitrogen, gallium, indium.

have having three valence electrons but silicon or germanium have four valance electrons. so, it forms only three covalent bonds. In the fourth covalent bond, only the germanium atom contributes one valence electron, while boron atom has no valence bonds. Hence, the fourth covalent bond is incomplete, having one electron short. This missing electron is known as a Hole. Thus, each boron atom provides one hole in the germanium crystal.

As an extremely small amount of boron impurity has a large number of atoms, therefore, it provides millions of holes in the semiconductor.

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