In semiconductors, free charge carriers are electrons and electron holes (electron-hole pairs). Electrons and holes are created by exciting electrons from the valence band to the conduction band. An electron-hole (often simply called a hole) is the lack of an electron at a position where one could exist in an atom or atomic lattice. It is one of the two types of charge carriers that are responsible for creating an electric current in semiconducting materials. Since, in a normal atom or crystal lattice, the negative charge of the electrons is balanced by the positive charge of the atomic nuclei, the absence of an electron leaves a net positive charge at the hole’s location. As electrons leave their positions, positively charged holes can move from atom to atom in semiconducting materials. When an electron meets with a hole, they recombine, and these free carriers effectively vanish. The recombination means an electron that has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes.
The conductivity of a semiconductor can be modeled in terms of the band theory of solids. The band model of a semiconductor suggests that at ordinary temperatures, there is a finite possibility that electrons can reach the conduction band and contribute to electrical conduction. In the semiconductor, free charge carriers (electron-hole pairs) are created by the excitation of electrons from the valence band to the conduction band. This excitation left a hole in the valence band, which behaves as a positive charge, and an electron-hole pair is created. Holes can sometimes be confusing as they are not physical particles in the way that electrons are. Rather they are the absence of an electron in an atom. Holes can move from atom to atom in semiconducting materials as electrons leave their positions.