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

We have investigated the photoluminescence excitation spectroscopy of GaAs-${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ separate confinement heterostructures consisting of a narrow GaAs quantum well embedded in a larger ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ one. Quantization of the energy in the "upper" large well is observed for thicknesses smaller than 750 Å. 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 ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ equal to (59 ± 3)% of the total band-gap difference for $x=0.13\mathrm{}$. This determination is also strongly supported by the good agreement between the observed and calculated transition energies in asymmetrical structures in which strong odd $\Delta n$ transitions appear.