Abstract
The transient response of low-temperature-grown GaAs was investigated with time-resolved photoreflectance (PR), photo-transmittance (PT), and photoconductivity (PC). The shape of the PR traces in the first few picoseconds was found to depend strongly on the wavelength. Despite of the drastic difference in appearance, these PR traces can all be well fitted by the sum of a fast positive, a fast negative and a slow positive component, each being obtained convolving a single-sided exponential function with the measured laser autocorrelation. The PT traces, however, can be decomposed into two positive components, one fast and one slow. The time constants of both the fast positive components coincide, and were attributed to the absorption bleaching by hot carriers and their subsequent cooling and trapping. The carrier-trapping time can be estimated by substracting the hot-carrier cooling time. The result was consistent with the PC measurements.