ULTRAFAST ENERGY RELAXATION PHENOMENA OF PHOTOEXCITED MINORITY ELECTRONS IN P-GAAS

Energy relaxation processes for minority electrons in p-GaAs are investigated by time-resolved photoluminescence (PL) measurements using an up-conversion technique with a high time resolution of 130 fs. By measuring the time evolution of PL intensity, the energy relaxation time of electrons is obtained directly. Moreover, electron distribution created by laser excitation which is in a thermally nonequilibrium state is successfully observed. With increasing hole concentration, the time response in PL intensity becomes fast. This implies that electron-hole interaction plays a key role in energy relaxation in high hole concentration. By detailed analyses of PL intensity, it can be found that the relaxation time by electron-hole interaction is approximately 500 fs or less, and electrons which are in a nonequilibrium state just after excitation are thermalized rapidly within about 200 fs at the first stage by electron-hole interaction.