Analysis of Semiconductor Devices
There are two complementary techniques of studying semiconductor devices:
The electrons in the valence band are not able of acquiring energy from external electric field and therefore do not contribute to the current. This band is not at all empty but may be partially or totally with electrons. On the contrary in the conduction band, electrons are seldom present. But it is probable for electrons to acquire energy from external field and thus the electrons in these bands contribute to the electric current. The forbidden energy gap is devoid of any of the electrons and this much energy is needed by electrons to jump from valence band to the conduction band.
Other words, in the case of conductors and semiconductors, like the temperature increases, the valence electrons in the valence energy move from the valence band to conductance band. Like the electron (negatively charged) jumps from valence band to conductance band, in the valence band there is a left out deficiency of electron that is called Hole (positively charged). Depending upon the value of Egap that is energy gap solids can be categorized as metals (conductors), insulators and semi conductors.