Phonon-driven carrier transport caused by short excitation pulses in semiconductors

We propose a simple model describing phonon-wind-driven transport of photoexcited carriers in bulk and in multiple-quantum-well (MQW) semiconductors. We take into account diffusion of carriers and primary acoustical phonons, generated at the final stage of the carrier’s relaxation, and show that their simultaneous action gives fast (even supersonic at higher excitation intensities) transport of photoexcited carriers. The phonon retardation effects are very essential in our approach. It is shown that this model may be applicable to recent experiments of Wolfe and collaborators [D. W. Snoke et al., Phys. Rev. B 41, 11 171 (1990); 44, 12 109(E) (1991); L. M. Smith et al., ibid. 39, 1862 (1989)] on fast transport of excitons in ${\mathrm{Cu}}_2$O and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs MQW’s.