Picosecond time-of-flight measurements of minority electrons in GaAs/AlGaAs quantum well structures.

We report direct measurements of drift velocities of photoexcited minority electrons in p-doped quantum well structures of GaAs/Al (0.48)Ga(0.52)As, using picosecond time-of-flight techniques. At low electric fields the electron mobility is strongly reduced by electron-hole scattering. At high fields (> 8 kV/cm) negative differential mobility is observed, which we interpret as real- space and valley transfer of hot electrons into the X-valley of Al(0.48)Ga(0.52)As. From the photoluminescence spectra, the carrier temperatures at which the transfer effects occur are determined.