Energetics and hydrogen passivation of carbon-related defects in InAs and In0.5Ga0.5As.

Abstract

We perform ab initio pseudopotential calculations for studying the stability of carbon-related defects and the atomic model for the hydrogen passivation of substitutional carbons in InAs. Among various C-related defects, the most stable one is found to be a substitutional C acceptor occupying an As site. As compared to GaAs, substitutional C impurities are found to have higher formation energies, due to large lattice distortions surrounding the C atom, thus, C incorporation into bulk InAs is more difficult. Because of the small atomic radius and deep atomic energy levels of C, when C occupies an In site, its defect energy level lies below the valence band maximum (VBM), and it behaves as an acceptor, however, the formation energy is much higher than for ${\mathrm{C}}_{\mathrm{As}}$. We note that an inversion between the VBM and the ${\mathrm{C}}_{\mathrm{In}}$ energy level takes place as pressure increases. For both the substitutional ${\mathrm{C}}_{\mathrm{As}}$ and ${\mathrm{C}}_{\mathrm{In}}$, we find that hydrogen neutralizes the electrical activity of acceptors by occupying a bond-centered site between the C atom and one of its neighbors. In an ${\mathrm{In}}_{0.5}$${\mathrm{Ga}}_{0.5}$As alloy, the C acceptor is found to favor an As site with In neighbors, with the formation energy lying between InAs and GaAs. Thus, the calculated acceptor concentration of ${10}^{17}$ -- ${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ is much lower than the maximum carrier density achievable in GaAs. \textcopyright{} 1996 The American Physical Society.