Question

Explain insulator and semiconductor on the basis of conduction of electricity.

Answer 1

Hint: Solids are classified into conductors, semi-conductors and insulators based on the conduction of electricity. In solid materials, electron energy levels form bands of allowed energies, separated by forbidden bands. They are valence band and conduction band.

Complete step by step answer:
Electrons in a completely filled band cannot move, since all states are occupied. Valence band is the outermost band filled with electrons. Conduction band is the next highest band to the valence band. The only way to move would be to jump into the next higher band and need energy. Electrons in a partly filled band can move, since there are free states to move. Solids are classified into three types based on their band structure-insulators, conductors and semiconductors.
Insulators are the metals with no or few free charge carriers. In insulators, the valence band is filled with electrons, so electrons cannot move within the valence band. Since the energy gap in insulators is large, it prevents this change in energy by the electrons. Thus insulators are poor conductors. E.g. quartz, wood, glass etc.
A semiconductor material is one whose electrical properties lie in between those of insulators and good conductors. Since the energy gap is very small and very little energy is needed to transfer electrons from the valence band into the conduction band. E.g. Germanium, Silicon

Note:The energy of more than the energy gap must be supplied to the electrons in the valence band, in order to transfer them into the conduction band. In terms of energy bands, semi-conductors can be defined as those materials which have almost an empty conduction band and almost filled valence band with a very narrow energy gap.