EXCITON LOCALIZATION IN INXGA1-XAS-GAAS COUPLED QUANTUM-WELL STRUCTURES

Using photoluminescence (PL) and photoluminescence excitation spectroscopy (PLE), we have studied a series of high-quality InxGa1-xAs-GaAs coupled multiple-quantum-well structures, grown by molecular-beam epitaxy. The samples are characterized by extremely sharp luminescence lines; the linewidths decreasing from 4 meV in a sample with wells of 48 A to 1 meV in a 14 A sample. In emission, all the samples exhibit a splitting of the luminescence line into two or three contributions. Splittings of the exciton peaks are also observed in the PLE spectra where, in all cases, the measured energy positions of the heavy-hole exciton creation peaks coincide exactly with the multiple PL lines. We explain our results in terms of small perturbations of either the alloy composition or the InxGa1-xAs thickness which have a dramatic effect on the spatial extent of the wave functions of these coupled quantum-well structures. Our calculations demonstrate that by introducing a small degree of randomness in the potential periodicity, the individual heavy-hole states become localized to a few potential wells, giving rise to the multiple exciton peaks observed in our optical data. © 1990 The American Physical Society.