Valence band
- The energy band formed by a series of energy levels containing valence electrons is known as valence band.
- This band is always filled with electrons.
- This is the band of maximum energy.
- Electrons are not capable of gaining energy from external electric field.
- No flow of current due to electrons present in this band.
- The highest energy level which can be occupied by an electron in valence band at 0 k is called Fermi level.
Conduction band
- The higher energy level band is called the conduction band.
- It is also called empty band of minimum energy.
- In this band is partially filled by the electrons.
- In this band the electrons can gain energy from external electric field.
- The electron is the conduction bands are called the free electrons. They are able to move anywhere within the volume of the solid.
- Current flow due to such electrons.
Holes In Semiconductors
- When an electron is removed from a covalent bond, it leaves a vacancy behind.
- A hole is considered as a seat of positive charge, having magnitude of charge equal to that of an electron.
- Holes acts as virtual charge, although there is no physical charge on it.
- Effective mass of hole is more than electron.
- Mobility of hole is less than electron.