A TIGHT-BINDING CALCULATION OF BAND DISCONTINUITIES IN THE ALXGA1-XAS/GAAS(ALAS) HETEROSTRUCTURES

Valence (ΔEv) and conduction (ΔEc) band discontinuities at the AlxGa1−x As alloy‐GaAs(AlAs) crystal interface are calculated within the tight‐binding approximation basing on the bulk electron properties of the individual components and taking into account the presence of a dipole layer at the interface. The alloy is considered in the virtual crystal approximation using the self‐consistent parameters of the sp3s* Hamiltonian obtained for the GaAs and AlAs crstals. The calculated value of the ratio of Qv = ΔEv/ΔE gΓ to Qc = ΔEc/ΔE gΓ, where ΔE gΓ is the difference between the direct band‐gap widths for the crystal and the alloy, is found to be 0.33:0.67 for all values of the Al concentration which is in good agreement with recent optical measurements. These parameters permit to obtain within the tight binding approximation the values of concentration x at which a direct‐indirect crossover occurs in the alloy (xc = 0.38) and a transition occurs from the first to the second type of heterojunction in the AlxGa1−xAs/AlAs structure (xc2 = 0.25), values being close to the experimental data. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA