Gamma -X mixing effects on pseudodirect exciton transitions in GaAs/AlAs type-II superlattices

Superlattice Calculation in an Empirical spds* Tight-Binding Model

We propose an empirical tight-binding method for tetrahedrally coordinated cubic materials and apply it to group IV and III-V semiconductors, extending existing calculations by the inclusion of all five d-orbitals per atom in the basis set. The symmetry character of the conduction states at the surface of the Brillouin zone is considerably improved compared to calculations in smaller bases, and the corresponding band positions can be obtained within the experimental uncertainties. Because the distance dependence of the tight-binding parameters is derived from deformation potentials, the model is particularly suited for an investigation of strained superlattices where the states at direct or pseudo-direct conduction band minima are composed of wavefunctions of all the minima at Γ, X, and L of the constituents. Investigations of GaAs/AlAs and short-period superlattices indicate a strong mixing between the conduction band valleys in the miniband structure, and the results are in better agreement with experiments than state-of-the-art empirical pseudopotential calculations.