Valence zone

The valence band is the energy region of the allowed electronic states in a solid filled with valence electrons .

In semiconductors at T = 0 (T is the absolute temperature ), the valence band is completely filled with electrons, and the electrons do not contribute to the electrical conductivity and other kinetic effects caused by external fields. At T> 0 K, thermal generation of charge carriers occurs, as a result of which part of the electrons passes to the conduction band located above or to impurity levels in the band gap . In this case, holes are formed in the valence band, which participate, along with electrons in the conduction band, in the transfer of electric current. Holes in the valence band can also occur during non-thermal excitation of a semiconductor — illumination, irradiation with a stream of ionizing particles, exposure to a strong electric field that causes an avalanche breakdown of the semiconductor, etc.