Conductors on the other hand have the conduction and valence bands overlapping. The interesting property of a semiconductor is that thermally excited electrons can move from the valence band to the conduction band and conduct current. Silicon and germanium have thermally excited electrons at room temperature and hence their common use in diodes and transistors. When an electron has been excited into the conduction band, the hole left behind in the valence band is also free to move through the crystal. A quantum mechanical treatment of this effect puts the hole on an approximately equal footing with the electron.
Temperature causes the thermal generation of electron-hole pairs.
One of the components of the pair will add a little to the majority charge carriers . The other component of the electron-hole pair will become the minority charge carrier . Minority charge carriers limit ideal performance and increase with increasing temperature. A common method for generating even more charge carriers in a semiconductor is by doping . That is, replacing a few atoms of the base material with atoms of a different element.