What are trivalent and pentavalent impurities?

Doping is the process of adding impurity atoms to intrinsic silicon or germanium to improve the conductivity of the semiconductor. The term impurity is used to describe the doping elements. Two element types are used for doping: trivalent and pentavalent. A trivalent element is one that has three valence electrons A pentavalent element is one that has five valence electrons. When trivalent atoms are added to intrinsic semiconductors, the resulting material is called a p-type material. When pentavalent impurity atoms are used, the resulting material is called an n-type material. The most commonly used doping elements are listed below.

Commonly Used Doping Elements

Trivalent Impurities

To make p-type

Aluminum (Al)

Gallium (Ga)

Boron (B)

Indium (In)

Pentavalent Impurities

To make n-type

Phosphorus (P)

Arsenic (As)

Antimony (Sb)

Bismuth (Bi)