Class 12 > Unit # 22:Solid State of Electronics > P type and N type semiconductors

Types of Extrinsic Semiconductors (N-Type and P-Type)

Detailed Video Lecture

1. N-type Semiconductor: When a Silicon crystal is doped with a pentavalent element, e.g., arsenic, antimony or phosphorous etc., four valence electrons of the impurity atom form covalent bonds with the four neighboring Si atoms, while the fifth valence electron provides a free electron in the crystal. Such a doped or extrinsic semiconductor is called an n-type semiconductor.

Figure illustrates a silicon crystal lattice doped with a pentavalent impurity such as antimony (Sb). The antimony atom is called a donor atom because it readily donates a free electron, which is thermally excited into the conduction band.

2. P-type Semiconductor: When a silicon crystal is doped with a trivalent element, e.g., aluminium, boron, gallium or indium etc., three valence electrons of the impurity atom form covalent bonds with the three neighboring Si atoms, while the one missing electron in the covalent bond with the fourth neighboring Si atom is called a hole, which in fact is a vacancy where an electron can be accommodated. Such a semiconductor is called a p-type semiconductor.

Figure illustrates a silicon crystal lattice doped with Boron (B). The Boron atom is called an acceptor atom because it is easy for the Boron ion core to accept a valence electron from a silicon atom, thus creating a hole in the valence band.