N dependence of the valence-band offset in (GaAs)n(AlAs)n: Role of charge redistribution, interface dipoles, and cation 3d states

A systematic study of the binding energy of core levels in (GaAs)n(AlAs)n (001) superlattices (nǍ3) was performed in order to assess the role of interface effects in the stabilization of the valence-band offset, a Ev, at the lattice-matched common-anion GaAs/AlAs (001) interface. Core levels were obtained from self-consistent all-electron local-density band-structure calculations of the superlattices. Sizable differences (ËǍ1/40.08 eV) for a Ev found using interface and bulk core levels for n=3 indicate that convergence is not achieved at distances too close to the interface. The n=1 value is found to give the correct offset only within ËǍ1/40.11 eV. The interface dipole potential, defined as the potential shift induced by the (planar-averaged) charge distribution of an electrically neutral region centered at the interface, is estimated to be ËǍ1/40.14 eV. Finally, the role played by the shallow cation 3d states on the band offset is analyzed and its importance is discussed.