Electronic states in near-surface quantum wells

We have calculated the energies and the spatial distributions of the electronic bound states of AlGaAs/GaAs near-surface quantum wells. We have employed a semi-empirical sp(3)s* tight-binding Hamiltonian including spin-orbit coupling, a Green function technique and the slab approximation. We have found blue shifts for the transition energies associated with the main optical transitions when the thickness of the AlGaAs top barrier decreases. The sign and the magnitude of these shifts agree quite well with the experimental data obtained recently. Both types of surface termination, cation and anion, are considered. In the case of As termination we have found a red shift for the transition energy of the first excited optical transition when the top barrier thickness decreases. An interpretation of these results in terms of the spatial distributions and orbital components of the electronic bound states is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.