Table of Contents
- Classification of semiconductors
- Classification of semiconductors on the basis of the source and the nature of the charge carriers
Classification of semiconductors
On the basis of their chemical composition. This scheme divides semiconductors broadly into elemental and compound semiconductors.
A. Elemental semiconductors:
Si and Ge.
B. Compound semiconductors:
Examples are:
(i) Inorganic: CdS, GaAs, CdSe, InP, etc.
(ii) Organic polymers: Polypyrrole, polyaniline, polythiophene, etc.
Both elemental and compound inorganic semiconductors are being largely used. After 1990, semiconductor devices using organic semiconductors and semiconducting polymers have been developed. This has signalled the futuristic technology of molecular-electronics and polymer-electronics.
Classification of semiconductors on the basis of the source and the nature of the charge carriers
Classification of semiconductors on the basis of the source and the nature of the charge carriers. This scheme divides semiconductors into intrinsic and extrinsic semiconductors as defined below:
A. Intrinsic semiconductors
The pure semiconductors (impurity less than 1 part in 1010) are called intrinsic semiconductors. The presence of the mobile charge carriers (electrons and holes) is an intrinsic property of the material, and these charges are obtained as a result of thermal excitation. Holes are essentially the electron vacancies with an effective positive charge. In an intrinsic semiconductor, the number density of electrons (ne) is equal to the number density of holes
B. Extrinsic semiconductors
The semiconductors obtained by adding or doping the pure semiconductor with small amounts of certain specific impurity atoms having valency different from that of the host atoms are called extrinsic semiconductors. Doping drastically changes the number density of mobile electrons and holes. The electrical conductivity of such semiconductors is essentially due to the foreign atoms i.e., extrinsic in nature.