Relaxation of hot carriers in undoped and n-doped Ga 0.47In 0.53As generated by subpicosecond pulses

Abstract

The cooling process of hot carriers in bulk Ga 0.47In 0.53As at 30 K is studied with subpicosecond time resolution. The time-dependence of the sample transmission at a wavelength of 1265 nm is measured after the generation of charge carriers with an excess energy lh ω-E g in the order of 200 meV and at densities of up to 7 × 10 17 cm −3. In an undoped sample, an almost double-exponential relaxation of the transmission change is found with time constants of about 1 ps and 10 ps, respectively. In contrast, a nearly single-exponential time behavior is observed in a n-doped sample with a time constant of 3 ps. The experimental data agree well with the results of model calculations that do not take into account “hot” phonon reabsorption by the carriers. The model reproduces the approximately double-exponential transmission relaxation of the undoped sample. The two time constants can be attributed to the population change of either the conduction or the heavy hole valence band states that are probed by the light pulses. The experimental data can be explained without assuming different temperatures of the electrons and the holes during the cooling process.