Nv. Chigarev et al., Coherent phonon emission in the supersonic expansion of photoexcited electron-hole plasma in Ge, PHYS REV B, 61(23), 2000, pp. 15837-15840
Coherent subnanosecond acoustic pulses generated by a laser-excited electro
n-hole plasma in a germanium single crystal are detected by a time-resolved
pump-probe photodeflection technique. It is found that the front duration
of these hypersound pulses is controlled by the time of plasma diffusion at
supersonic velocities. The characteristic velocity of plasma diffusion eva
luated from the experiments exceeds the longitudinal sound velocity in germ
anium by a factor of 1.5. The hypersound pulse shapes provide evidence for
supersonic diffusion of the electron-hole plasma in a semiconductor at room
temperature on a subnanosecond time scale.