Limits on band discontinuities in GaAs-GaAlAs heterostructures deduced from optical photoresponse

Abstract

Sharp transitions have been observed in the photoconductivity of GaAs-GaAlAs multi-quantum wells at energies greater than the energy gap of GaAs, corresponding to both allowed and forbidden excitonic transitions between electron and hole sub-bands in the quantum wells. Transition energies have been analysed using the Bastard envelope function model, with the energy band offset and well width as variable parameters, and the model has been found not to give an accurate description of the energy levels involved. A simpler empirical approach has been used to yield limits on the distribution of band discontinuity between conduction and valence bands; these limits are found to disagree with the previously accepted value Delta E_c=0.85 Delta E_g, suggesting the valence band discontinuity is greater than previously thought.