explain conduction band theory brifly ?

Asked by gargimoitreyee | 12th Mar, 2018, 11:51: PM

Expert Answer:

In most of the solids, conduction takes place due to the migration of electrons under the influence of electric field. However, in ionic compounds, the movement of the ion is responsible for their conducting behaviour. In metals, conductivity strongly depends upon the number of valence electrons available in an atom.A band is formed due to the closeness of molecular orbitals which are formed from atomic orbital.If this band is partially filled or it overlaps the unoccupied higher energy conduction band, the electrons can flow easily under an applied electric field and the solid behaves as a conductor.If the gap between valence band and next higher unoccupied conductions band is large, electrons can not jump into it and such a substance behaves as an insulator.
If the gap between the valence band and conduction band is small, some electrons may jump from valence band to the conduction band. Such a substance show some conductivity and it behaves as a semiconductor [Fig(c)]. An increase in temperature will increase the electrical conductivity of semiconductors as more electrons can jump from valence to conduction band. Silicon and germanium show this type of behaviour and are called intrinsic semiconductors.Doping: The process of introducing an impurity into semiconductors to enhance their conductivity is called doping.n-type semiconductor. When silicon or germanium crystal is doped with a group 15 element like Por As, the dopant atom forms four covalent bonds like a Si or Ge atom but the fifth electron, not used in bonding, becomes delocalised and contributes its share towards electrical conduction.Thus, silicon or germanium doped with P or As is called n-type semiconductor, n indicative of negative since it is the electron that conducts electricity.p-type semiconductor: When silicon or germanium is doped with a group 13 element like B or Al, the dopant atom forms three covalent bonds like a B or Al atom, but in place of the fourth electron, a hole is created. This hole moves through the crystal like a positive charge giving rise to electrical conductivity. Thus, Si or Ge doped with B or Al is called p-type of semiconductor (p stands for the positive hole), since it is the positive hole that is responsible for conduction.

Answered by Ramandeep | 13th Mar, 2018, 11:24: AM