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 str uctures of the constituent atomic species. The electronic structures a re calculated using first-principles pseudopotentials. The wavefunctio ns of valence and conduction bands are projected on s, p and d symmetr y orbitals. The resulting information on the orbital composition of cr ystalline states is combined with eigenenergies of Al and Ga atoms in order to explain differences between band energies of the two semicond uctors. For GaAs, the dependence of the orbital composition of wavefun ctions on the wavevector is analysed in detail, and correlated with th e dispersion of energy bands. The contribution of excited d orbitals t o the lowest conduction states at X and L points is as high as about 5 0 per cent, and is responsible for the decrease of the indirect invert ed right perpendicular -X optical bandgap with hydrostatic pressure. T he validity of the sp(3) minimal-basis-set tight-binding model is eval uated.