  Coherent super-high-frequency (SHF) vibrations provide an excellent tool for
the modulation and control of excitations in semiconductors. Here, we
investigate the piezoelectric generation and propagation of longitudinal bulk
acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using
bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We
show that the electro-acoustic conversion efficiency of the BAWRs depends
sensitively on the sputtering conditions of the ZnO films. The BAWRs were then
used for the study of the propagation properties of the LBAWs in GaAs in the
frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K,
respectively, which have so far not been experimentally accessed. We found that
the intrinsic acoustic absorption of GaAs in the temperature range from 80 K to
300 K is dominated by scattering with thermal phonons. At lower temperatures,
in contrast, the intrinsic acoustic absorption saturates at a
frequency-dependent value. Experiments carried out with different propagation
lengths indicate that the saturation is associated with losses during
reflection at the sample boundaries. We also demonstrate devices with high
quality factor fabricated on top of acoustic Bragg-reflectors. The results
presented here prove the feasibility of high-quality acoustic resonators
embedding GaAs-based nanostructures, thus opening the way for the modulation
and control of their properties by electrically excited SHF LBAWs.
