Spectroscopic determination of the bandgap crossover composition in MBE-grown AlxGa1−xAs

Abstract

The aluminum concentration dependence of the energies of the direct and indirect bandgaps arising from the Γ and X conduction bands are measured at 1.7 K in the semiconductor alloy AlxGa1−xAs. The composition at which the bands cross is determined from photoluminescence of samples grown by molecular-beam epitaxy very close to crossover at x ≈ 0.4. The use of resonant laser excitation and the improved sample linewidth allows excitation intensities as low as 10−2 W/cm2, giving a precise determination of the bound exciton transition energies and their Γ and X crossover. Photoluminescence excitation spectroscopy is then used to measure the binding energies of the donor-bound excitons and the Γ free exciton binding energy. After correcting for the Γ- and X-dependence of these quantities, the crossover of the bandgap is determined to be at x = 0.401 and E = 2.086 eV.