The semiconductors are further classified into intrinsic semiconductors and extrinsic semiconductors.
Intrinsic semiconductors
A semiconductor in which holes and electrons are created only by thermal excitation across the energy gap is called an intrinsic semiconductor. A pure crystal of silicon or germanium is an intrinsic semiconductor.
In an intrinsic semiconductor the number of holes in the valence band is equal to number of electrons in the conduction band. The Fermi level for an intrinsic semiconductor lies at midway in the forbidden gap. It behaves as an insulator at absolute temperature ( T=0 K).
Extrinsic semiconductors
Extrinsic semiconductors are impure form of semiconductor [doped semiconductors]. By the process of doping, the impurities are added in the intrinsic semiconductors by which the holes and free electrons are produced. The effect of impurity states reduces the band gap up to 0.01eV and increases the electrical conductivity.
If pentavalent (Phosphorous, arsenic, antimony) impurities are doped, then the free electrons are produced, this semiconductor is called N-type semiconductor.
If trivalent [Aluminium, Gallium, Indium] impurities are doped, then the holes are produced, then this semiconductor is called P-type semiconductor.
- N – type and
- P – type.
Difference between N-type and P-type semiconductor
| S. No | N-type | P-type |
| 1. | It is donor type. | It is acceptor type. |
| 2. | Impurity atom is pentavalent. | Impurity atom is trivalent. |
| 3. | There is donor level. | There is acceptor level. |
| 4. | Donor level lies close to the bottom of the conduction band. | Acceptor level lies close to the top of the valance band. |
| Read More Topics |
| Difference between N & P type semiconductor |
| Carrier concentration in metals |
| Variation of carrier concentration with temperature |
