1.3 Classification of solids on the basis of band theory

  Semi-conductor Devices and Electronics

    1.0 Introduction
    2.0 Types of semiconductor
    3.0 Mass action law
    4.0 Electrical conductivity in semiconductor
    5.0 $p-n$ junction
    6.0 Breakdown voltage
    7.0 $I-V$ characteristics of a $p-n$ junction
    8.0 Rectifier
    9.0 Light emitting diode (LED)
    10.0 Zener diode
    11.0 Transistor
    12.0 Boolean identities
    13.0 Logic gates
    14.0 De Morgan's theorem

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1.3 Classification of solids on the basis of band theory

A. Metals

In metals either the conduction band is partially filled or conduction band & valence band partially overlap each other.
In metals, there is no forbidden energy gap between the valence and conduction bands.

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B. Insulators

In insulators, the valence band is completely filled and conduction band is completely empty.
In insulators, there is a very wide forbidden energy gap between the valence and conduction bands.
In insulators, the forbidden energy gap is more than $3\ eV$.

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C. Semiconductors

In semiconductors, the valence band is completely filled and conduction band is empty.
In semiconductors, the forbidden energy gap between the valence and the conduction band is small.
The forbidden energy gap is less than $3\ eV$.
For silicon, the forbidden energy gap is $1.1\ eV$ and for germanium, it is $0.72\ eV$.
At absolute zero, semiconductors behave as a perfect insulator.

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