Introduction to Semiconductor

Introduction to Semiconductor

 Introduction Certain substances like germanium, silicon, carbon etc. are neither good conductors like copper nor insulators like glass. The resistivity of these materials lies in between conductors and insulators. Such substances are classified as semiconductors. Semiconductors have some useful properties and are being extensively used in electronic circuits. Semiconductor A semiconductor is a substance which has resistivity 10-4 to 0.5 Ω-m in between conductors and insulators e.g. germanium, silicon, selenium, carbon etc. The following table shows the resistivities of different types of materials.
Sl No
Substance
Nature
Resistivity
1
Copper
Good conductor
1.7 X 10-8 Ω-m
2
Germanium
Semiconductor
0.6 Ω-m
3
Glass
insulator
9 X 1011 Ω-m
4
Nichrome
resistance material
10-4 Ω-m
Properties of Semiconductors i) The resistivity of a semiconductor is less than an insulator but more than a conductor. ii) Semiconductors have negative temperature coefficient of resistance i.e. the resistance of a semiconductor decreases with the increase in temperature and vice versa. iii) When a suitable metallic impurity e.g. arsenic, gallium etc is added to a semiconductor, its current conducting properties change appreciably.