ATOMIC-ORBITAL INTERPRETATION OF ELECTRONIC-STRUCTURE OF III-V SEMICONDUCTORS - GAAS VERSUS ALAS

We link the electronic structures of AlAs and GaAs with the energy structures of the constituent atomic species. The electronic structures are calculated using first-principles pseudopotentials. The wavefunctions of valence and conduction bands are projected on s, p and d symmetry orbitals. The resulting information on the orbital composition of crystalline states is combined with eigenenergies of Al and Ga atoms in order to explain differences between band energies of the two semiconductors. For GaAs, the dependence of the orbital composition of wavefunctions on the wavevector is analysed in detail, and correlated with the dispersion of energy bands. The contribution of excited d orbitals to the lowest conduction states at X and L points is as high as about 50 per cent, and is responsible for the decrease of the indirect inverted right perpendicular -X optical bandgap with hydrostatic pressure. The validity of the sp(3) minimal-basis-set tight-binding model is evaluated.