Question

please explain me flow of current in semiconductor using conduction band and valence band

Answer 1

Energy Bands
In an isolated atom the valence electrons can exist only in one of the allowed orbitals each of a sharply defined energy called energy levels. But when two atoms are brought nearer to each other, there are alterations in energy levels and they spread in the form of bands.
Energy bands are of following types:
1. Conduction band
2. Valence band

Answer 2

Valence band:

The energy band formed by a series of energy levels containing valence electrons is known as valence band. At 0 K, the electrons fills the energy levels in valence band starting from lowest one.
(i) This band is always filled by electrons.
(ii) This is the band of maximum energy.
(iii) Electrons are not capable of gaining energy from external electric field.
(iv) No flow of current due to such electrons.
(v) The highest energy level which can be occupied by an electron in valence band at 0 K is called Fermi level.

Answer 3

Conduction band:

The higher energy level band is called the conduction band.
(i) It is also called empty band of minimum energy.
(ii) This band is partially filled by the electrons.
(iii) In this band the electrons can gain energy from external electric field.
(iv) The electrons in the conduction band are called the free electrons. They are able to move anywhere within the volume of the solid.
(v) Current flows due to such electrons.

Answer 4

The electrons in the conduction band are free to move in the solid and when we apply some field then those electrons starts flowing in some particular direction which constitute current.

At T=0K, all the electrons are in valence band while conduction band is empty.

Now as we increase the temperature then even at room temp. the electrons acquires some definite energy to jump from the valence band to conduction band and since in the conduction band electrons can move freely, so they will constitute current.