classification of material like insulators, metal and semiconductor are done on the basis of valance band and conduction band.
Semiconductor Electronics: Materials, Devices and Simple circuits (part-1)
What is Insulator? What are semiconductors? What is Metal.? Explain the energy supply in semiconductor, metal and semiconductor.
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Metals have low resistivity (10–2 to 10–8 Ωm), insulators have very high resistivity (>108 Ωm–1), while semiconductors have intermediate values of resistivity. In Insulator valance band and conduction band are separated by large energy gap. This much energy cannot be supplied from outside therefore conduction is not possible in Insulators. In semiconductors the gap between valance band and conduction has small energy gap. This much energy can be supplied from outside and hence in conduction is possible. In metals or conductors there is no energy gap and conduction band, it means electors are already free to move.