Sharp-line photoluminescence spectra from GaAs-GaAlAs multiple-quantum-well structures

The photoluminescence spectra from four ${\mathrm{Al}}_{0.25}$ ${\mathrm{Ga}}_{0.75}$As-GaAs multiple-quantum-well (MQW) structures with well thicknesses of 100, 200, 300, and 400 Å and barrier thicknessess of 100 Å have been interpreted. The extrinsic emission is predominantly in the donor region. A number of very sharp transitions have been observed for the first time. Several of the transitions are no more than 0.15 meV in width. The light- and the heavy-hole free excitons were observed in the 400 Å well. The heavy-hole free excitons were observed in the other wells. The radiative transitions associated with the neutral-donor bound excitons as well as the free-to-bound and neutral-acceptor bound excitons are discussed. Magnetic field splittings were observed for several of the optical transitions. These data together with the diamagnetic shifts and excitation-dependent measurements are used in the identification of the multiple-quantum-well transitions.