Localized defects in III-V semiconductors

A Green's-function approach, closely related to that of Koster and Slater, is developed, within the one-electron pseudopotential formalism. This is applied to single vacancies, the divacancy and vacancy-oxygen pairs in GaAs, and single vacancies in GaP and InSb. A number of localized states are found. It is shown that the properties of the host-crystal band structure, the electron-electron interaction, and lattice relaxation play an important part in the formation of these states. In contrast with the Koster-Slater calculations, our results are not very sensitive to the strength of the vacancy potential. Our calculations indicate that As and Ga vacancies in GaAs should behave as single donors and acceptors, respectively. The $V_{\mathrm{Ga}}-\mathrm{O}$ complex behaves as a deep neutral center. The wave functions associated with the levels introduced into the band gap are highly localized. Since they contain admixtures of both valence- and conduction-band functions, and exhibit large lattice distortion, they are likely to take part in nonradiative recombination processes. Finally, we note that nonradiative recombination via some deep neutral centers is likely to be very efficient since our calculation also indicates a possibility of localized excited states introduced by these centers.