Types of Semiconductors
Semiconductors are of two types:
Pure or intrinsic semiconductor
Impure or extrinsic semiconductor
Intrinsic Semiconductor: The pure semiconductors in which the electrical conductivity is totally governed by the electrons excited from the valence band to the conduction band and in which no impurity atoms are added to increase their conductivity are called intrinsic semiconductors and their conductivity is called intrinsic conductivity. Electrical conduction in pure semiconductors occurs by means of electron-hole pairs. In an intrinsic semiconductor-
ne = nh = ni
where ne = the free electron density in conduction band, nh = the hole density in valence band, and ni = the intrinsic carrier concentration.
Extrinsic Semiconductors: A Semiconductor doped with suitable impurity atoms so as to increase its conductivity is called an extrinsic semiconductor.
- Types of Extrinsic Semiconductors: Extrinsic semiconductors are of two types:
- n-type semiconductors
- p-type semiconductors
n-type semiconductors: The pentavalent impurity atoms are called donors because they donate electrons to the host crystal and the semiconductor doped with donors is called n-type semiconductor. In n-type semiconductors, electrons are the majority charge carriers and holes are the minority charge carriers. Thus,
p-type semiconductors: The trivalent impurity atoms are called acceptors because they create holes which can accept electrons from the nearby bonds. A semiconductor doped with acceptor type impurities is called a p-type semiconductor. In p-type semiconductor, holes are the majority carriers and electrons are the minority charge carriers Thus,