Relaxation process of photoexcited carriers in GaAs structures with low-temperature-grown layers

Spatial relaxation processes of photoexcited carriers in GaAs structures are studied by means of photoluminescence spectroscopy. A single GaAs/Al_0.3Ga_0.7AS quantum well and a low-temperature-grown GaAS (LT-GaAs) layer containing a high concentration of excess arsenic are placed in a GaAs structure as optical markers; the former serves as the radiative recombination site, while the latter as the trapping site of photoexcited carriers. The photoluminescence intensity from the quantum well is significantly reduced by the presence of a LT-GaAs layer immediately next to a barrier layer. The effect of the LT-GaAs layer is exponentially enhanced as a thickness of the barrier layer decreases. The results suggest that once an excess As point defect is placed within an extent of a wave function of a photoexcited carrier, trapping of the photiexcited carrier occurs at an extremely fast rate. In a structure where a LT-GaAs is placed at a distant location from the quantum well, the photoluminescence intensity from the quantum well is weakly dependent on the location of the LT-GaAs layer as expected from thermal diffusion of photoexcited carriers to trap sites as semiclassical particles