Investigation of GaAs/(Al,Ga)As multiple quantum wells by photoreflectance

Room‐temperature photoreflectance has been used to investigate a series of GaAs/(Al,Ga)As multiple quantum‐well structures. In addition to the allowed (as high as n=5) and symmetry forbidden transitions, we have observed transitions involving the so‐called ‘‘unconfined’’ states, which have received less attention so far. We have examined these transitions more carefully by studying a low barrier multiple quantum‐well structure and observed transitions as far as 200 meV beyond the barrier gap. By using a simple two‐band tight‐binding model, the energies and matrix elements for these unconfined transitions were calculated and shown to agree with the experimental values determined by fitting the photoreflectance spectra to the theoretical line‐shape expression.