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/Al0.48Ga0.52As, 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 Al0.48Ga0.52As. From the photoluminescence spectra the carrier temperatures at which the transfer effects occur are determined.