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

Abstract

We have investigated the photoluminescence excitation spectroscopy of GaAs-${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ separate confinement heterostructures consisting of a narrow GaAs quantum well embedded in a larger ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ one. Quantization of the energy in the "upper" large well is observed for thicknesses smaller than 750 \AA{}. 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 ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ equal to (59 \ifmmode\pm\else\textpm\fi{} 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 $\ensuremath{\Delta}n$ transitions appear.