A Tight‐Binding Calculation of Band Discontinuities in the Al x Ga 1− x As/GaAs(AlAs) Heterostructures

Valence (ΔE v ) and conduction (ΔE c ) band discontinuities at the Al x Ga 1− 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 sp 3 s* Hamiltonian obtained for the GaAs and AlAs crstals. The calculated value of the ratio of Q v = ΔE v /ΔE   g Γto Q c = ΔE c /ΔE   g Γ , where ΔE   g Γis 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 ( x c = 0.38) and a transition occurs from the first to the second type of heterojunction in the Al x Ga 1− x As/AlAs structure ( x c2 = 0.25), values being close to the experimental data.