Excitation and detection of high-frequency coherent acoustic phonons in low-symmetry superlattices

Abstract

The generation and detection of coherent acoustic phonons in GaAs/AlAs superlattices grown on the low-symmetry, (311) and (211), planes of GaAs using femtosecond time-resolved pump-probe measurements is described. Frequencies of the excited phonons are deduced from the oscillations in the surface reflectivity of the probe and are compared with theoretical calculations assuming that Raman scattering is responsible for coherent phonon generation. The measured frequencies and relative intensities of the modes agree well with the theoretically predicted folded bulk acoustic modes and are determined by the period and symmetry of the superlattices.