EFFECTS OF LOCALIZATION ON OPTICAL-SPECTRA FOR SHALLOW ACCEPTORS IN CENTER-DOPED GAAS/ALGAAS MULTIPLE QUANTUM-WELLS

A spectroscopic study of narrow quantum wells doped with shallow acceptors is presented, employing tunable resonant laser excitation in both CW and transient mode. The picosecond transient data directly demonstrate the spectral diffusion of both localized free excitons (FE's) and bound excitons (BE's), if they are resonantly excited at sufficiently high photon energies. Similar data taken with resonant CW excitation show a sharp BE peak resonantly excited via localized excitons (LE's), allowing a precise determination of the binding energy of bound excitons. At lower photon energies sharp Raman peaks are observed and identified as shake-up two-hole processes for the acceptors, as well as LO phonon replica enhanced by localization at interface potentials. Similar resonant Raman shake-up processes are seen for the FE. The same replica processes occur in nonresonant luminescence, as shown by the background in the spectra.