The spatial expansion of the photoexcited electron-hole plasma created by picosecond-pulse laser excitation in $\mathrm{GaAs}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multiple-quantum-well structures is investigated by time-resolved Raman scattering on a picosecond time scale. The experimental results show that the measured drift velocity of the plasma is comparable to its Fermi velocity. Consequently, our measurements demonstrate that the transport of the photoexcited electron-hole plasma in $\mathrm{GaAs}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells is thermodiffusive.

• Received 16 June 1986

DOI:https://doi.org/10.1103/PhysRevB.34.6018