Binding energies of acceptors in GaAs–AlxGa1−xAs quantum wells

Abstract

We have used the variational method to calculate the acceptor binding energies in GaAs–AlxGa1−xAs quantum wells. The calculation includes the coupling of the top four valence bands of both materials in the multiband effective mass approximation. To ensure the convergence of the calculation, a large number of basis functions which are made up of the s-like or d-like spatial states multiplied by j=3/2 spinors are used for the expansion of the acceptor wave function. Because the quantum well potential reduces the symmetry from Td to D2d, the bulk Γ8 acceptor ground state splits into Γ6 and Γ7 states. The Γ6 state is predominantly derived from the heavy-hole subband and the Γ7 state is predominantly derived from the light-hole subband. We have calculated the binding energies of the Γ6 state (measured from the top of the heavy-hole subband) and the Γ7 state (measured from the top of the light-hole subband) for both center doped and edged doped quantum wells for various barrier heights as functions of well width. Except for well widths smaller than ≊40 Å, the Γ7 binding energy is greater than the Γ6 binding energy. In recent studies, the photoluminescence resulting from the acceptor levels to conduction band transition in MBE grown GaAs–AlGaAs superlattices has been measured. Our theoretical results are in excellent agreement with these experimental data.