Theory of carriers bound to In isoelectronic δ-doping layers in GaAs

We present a model for ultrathin InAs impurity interlayers embedded in bulk GaAs. It is based on an empirical tight-binding Green's function scheme with basis functions that are Bloch-like in the in-plane direction and Wannier-like perpendicular to it. Spin-orbit interaction and strain are consistently included. Our results are in good agreement with recent experimental data as far as the heavy-hole-electron transition is concerned. Conversely, our calculations indicate that one layer of InAs in bulk GaAs induces a light-hole state degenerate with the continuum 3 meV below the GaAs valence-band edge. This is in contrast with effective-mass calculations that predict a type-I light-hole configuration in this system. The importance of strain in leading to this energy-level configuration is stressed. We suggest that absorption or temperature-dependent luminescence experiments could distinguish between a bound or an unbound light-hole state.