INTERISLAND EXCITON MIGRATION AND ENHANCED BOUND EXCITON RECOMBINATION IN AN ALGAAS GAAS QUANTUM-WELL STRUCTURE GROWN BY MOLECULAR-BEAM EPITAXY WITHOUT GROWTH INTERRUPTIONS AT INTERFACES/

Low-temperature excitonic effects in a high-quality AlGaAs/GaAs single quantum well (25 monolayers wide) structure grown without growth inte rruptions at the interface were studied using steady-state, time-resol ved and photoluminescence excitation spectroscopy. Heavy-hole free exc iton and impurity (neutral donor) bound exciton emissions, associated with quantum well regions (islands) 24 and 25 monolayers wide, have be en resolved and identified using excitation energy resonant with the h eavy-hole exciton energy. Interisland exciton migration, until now rep orted only for growth interrupted structures, is observed, indicating that islands formation is not a specific property of growth interrupte d structures. We estimate the rate of transfer of free excitons betwee n regions of width 24 monolayers and 25 monolayers to be 290 ps(-1). W e show that the relative intensity of free-to-bound excitonic emission s strongly depends on interface morphology and that enhanced bound exc iton recombination is observed under some conditions. The relevant mec hanisms of such enhanced bound exciton recombination are proposed.