Electronic structures of GaAs/InAs(001) thin-layer systems: A tight-binding approach

The electronic structure of an InAs monolayer in bulk GaAs (001) is calculated in the framework of the sp³s* tight-binding model, which includes only nearest-neighbour interactions The results show that both electrons and holes are localized around the inserted InAs plane, which is, therefore, playing the role of a quantum well for all charge carriers. The eigenfunctions of the confined electron and hole, calculated at the Γ point, are found to be supported by the s, p_z, and s* orbitale of atoms in the neighbourhood of the inserted In layer, and hence to be confined in the c-axis direction, with a localization length of the order of 110 Å. In the limit of a single InAs monolayer in bulk GaAs, the energy gap is found to be 40 meV less than that of bulk GaAs. These results are in excellent agreement with the results of photoluminescence (PL) experiments, and successfully explain the observed intense PL peak, and its polarization parallel to the interface. Moreover, in a system composed of two InAs monolayers separated by N monolayers of GaAs, the localization of charge carriers around the InAs planes is found to decrease when N becomes large, as a consequence of the increase of the confinement energies. The calculated band-gap energies as a function of N are in reasonable agreement with the PL experimental data.