EXTENDED, MONOLAYER FLAT ISLANDS AND EXCITON DYNAMICS IN GA0.47IN0.53AS/INP QUANTUM-WELL STRUCTURES

Spectroscopic studies are performed on multiple-quantum-well structures of Ga0.47In0.53As/InP grown by low-pressure, metal-organic vapor-phase epitaxy. The compositional gradient and thickness variation at interfaces are probed by exciton recombination in the quantum wells. Spectral and topological observations of extended, monolayer flat islands are demonstrated by photoluminescence and cathodoluminescence. Different exciton transfer mechanisms are studied by the temperature-dependent, photoluminescence spectroscopy of these quantum-well structures. Depending on the temperature, in addition to exciton localization in the extended monolayer flat islands, exciton migration within the quantum well, i.e., intralayer (lateral) transfer, occurs as well as thermal detrapping to the InP barrier and subsequent recapture into neighboring, thicker quantum wells, i.e., interlayer (perpendicular) transfer. Rates for carrier capture into quantum wells in the ps range are extracted from the temperature dependence of quenching processes of photoluminescence. Quantitative analysis of exciton migration is carried out based on absorption measurements. The results show that due to exciton migration, attempts to estimate the area ratio of monolayer islands of different thicknesses by luminescence intensities result in a severely distorted picture, with the area of thicker islands being greatly over estimtated.