THEORY OF CARRIERS BOUND TO IN ISOELECTRONIC DELTA-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 direc tion and Wannier-like perpendicular to it. Spin-orbit interaction and strain are consistently included. Our results are in good agreement wi th recent experimental data as far as the heavy-hole-electron transiti on is concerned. Conversely, our calculations indicate that one layer of InAs in bulk GaAs induces a light-hole state degenerate with the co ntinuum 3 meV below the GaAs valence-band edge. This is in contrast wi th effective-mass calculations that predict a type-I light-hole config uration in this system. The importance of strain in leading to this en ergy-level configuration is stressed. We suggest that absorption or te mperature-dependent luminescence experiments could distinguish between a bound or an unbound light-hole state.