Acceptor atom

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An impurity atom in a semiconductor which can accept or take up one or more electrons from the crystal and become negatively charged. An atom which substitutes for a regular atom of the material but has one less valence electron may be expected to be an acceptor atom. For example, atoms of boron, aluminum, gallium, or indium are acceptors in germanium and silicon (illus. a), and atoms of antimony and bismuth are acceptors in tellurium crystals. Acceptor atoms tend to increase the number of holes (positive charge carriers) in the semiconductor (illus. b). The energy gained when an electron is taken up by an acceptor atom from the valence band of the crystal is the ionization energy of the atom. See also Donor atom; Semiconductor.

tetravalent host atom, by completing the four tetrahedral covalent bonds with its nearest neighbor silicon atoms. This requires an electron to be accepted from the valence band, thus making boron negatively charged. (b) Energy diagram showing that the absence of an electron in the valence band is equivalent to a positive charge carrier, a hole, which is bound to boron via Coulomb attraction with an ionization enerzy EI ċ Eg = energy gap separating valence band from conduction band.">
Trivalent acceptor atom, boron (B), in the elemental semiconductor silicon (Si). (a) Boron atom in a substitutional position, that is, replacing silicon, a tetravalent host atom, by completing the four tetrahedral covalent bonds with its nearest neighbor silicon atoms. This requires an electron to be accepted from the valence band, thus making boron negatively charged. (b) Energy diagram showing that the absence of an electron in the valence band is equivalent to a positive charge carrier, a hole, which is bound to boron via Coulomb attraction with an ionization enerzy EI ċ Eg = energy gap separating valence band from conduction band.