Self-consistent study of confined states in thin GaAs-AlAs superlattices

Abstract

We have investigated the (GaAs)1-(AlAs)1 and (GaAs)4-(AlAs)4 superlattice heterostructures in the [001] orientation by using the self-consistent pseudopotential method within the local-density formalism. The stability of the (GaAs)1-(AlAs)1 superlattices with respect to the constituent compounds and the electronic energy structure are analyzed. The ordered GaAlAs2 phase is found to be energetically less stable relative to the disproportionation into its constituent binary compounds. Self-consistent charge distribution reveals that the bond charge maximum of the AlAs bond increases at the expense of the GaAs bond upon superlattice formation. We found (GaAs)1-(AlAs)1 is an indirect band-gap material, whereas (GaAs)4-(AlAs)4 in a direct band-gap material. The crystal field in (GaAs)4-(AlAs)4 gives rise to splitting in the conduction-band minima. Charge distributions of three conduction-band states one from the and two from the M point of the superlattice Brillouin zone show a confined character. Their confinement suggests a staggered band lineup, AlAs being the quantum well for the conduction-band electrons. This band lineup is different from that which occurs in superlattices with large periodicity, but is in agreement with the experimental data obtained from very thin GaAs-AlAs superlattices. © 1987 The American Physical Society.