Electronic structure of quantum-well states revealed under high pressures

We report on electronic and optical properties under pressure of GaAs AlxGa1-xAs multi-quantum-wells and superlattices versus well-width and composition x. Photoluminescence measurements are used together with full-scale pseudopotential simulation of electronic structure. Λ1e-Λ1hh transition intensity thresholds mark level degeneracy with the AlxGa1-xAs X-band edge, shifted in the heterostructures by valence-band offset-induced staggered band alignment. In SLs, indirect-gap spatially quantized electron states formed within the subsidiary X bands are observed experimentally and modelled theoretically. These new X-derived states are located within the AlxGa1-xAs and optical transitions occur across both k-space and the hetero-interface. We thus obtain direct optical measure of the GaAs AlxGa1-xAs band offsets, giving ΔEv ∼- (0.32 ± 0.02)ΔEgΓ across the alloy system. Intervalley "mixing" connecting the quantized electron states of differing k-value is also explored, as crossings between them are induced under pressure. Energy levels, transition energies and intensities, radiative lifetimes, level perturbations (anticrossings), and oscillator strengths have been obtained with good agreement between experiment and theory. We show that coupling between the familiar zone-center quantum-well states and the new zone-edge states is significant and observable, and must be taken into account for full description of quantum-well states in multi-valley semiconductors. © 1988.