1.05 Electron-Hole pair generation
As previously stated there is an energy gap between the conduction and valence band in semiconductors. However the energy required to jump this gap can be supplied to the electrons from heat energy. (This means that if the material is heated some electrons will acquire enough energy to break free of their parent atoms to become free electrons.) At room temperature some electrons will have acquired the energy to jump into the conduction band. If the temperature is increased so will the number of electrons in the conduction band. This process is called electron-hole pair generation. This is because by supplying energy we transfer an electron from the valence band to the conduction band. This produces a free electron in the conduction band and leaves a hole (vacant electron position) in the valence band.
The free electrons are now available to contribute to an electrical current if a voltage is applied to the material. Also the holes (the vacant electron positions) in the valence band will now allow movement of electrons in the valence band, this can also contribute to an electrical current. The net effect is that heat increases the conduction properties of a pure semiconductor.