Phonon transport in photoexcited GaAs

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Abstract
The thermalization of photoexcited carriers in GaAs at low temperatures can lead to the excitation of long-lived, high-frequency (∼ 1 THz) acoustic phonons. Experimental results are reported for liquid-encapsulated-Czochralski-grown GaAs which substantially clarify the effect of various experimental parameters on the time-resolved phonon transport. We report, for the first time, a significant broadening of the phonon pulse shape for laser excitation energies close to but below the direct band gap of GaAs (1.519 eV). In addition, we observe phonon pulse narrowing for a higher temperature (4.2 K) than previously reported (3.7 K). These results provide strong support for a significant contribution of high-frequency phonons to the observed phonon pulse shapes. Preliminary evidence for anisotropic defect scattering of high-frequency phonons is also presented.