Size quantization and band-offset determination in GaAs-GaAlAs separate confinement heterostructures

We have investigated the photoluminescence excitation spectroscopy of GaAs-Ga_1-xAlₓAs separate confinement heterostructures consisting of a narrow GaAs quantum well embedded in a larger Ga_1-xAlₓAs one. Quantization of the energy in the "upper" large well is observed for thicknesses smaller than 750 {}. The peculiar structure configuration allows the observation of transitions which are strongly dependent on the conduction- and valence-band discontinuities. Comparison between theory and experiment gives a conduction-band offset between GaAs and Ga_1-xAlₓAs equal to (59 ±{} 3)% of the total band-gap difference for $x=0.13$. This determination is also strongly supported by the good agreement between the observed and calculated transition energies in asymmetrical structures in which strong odd Δn transitions appear.