Spin relaxation of electrons in graded doping strained GaAs-layer photocathode of polarized electron source

A graded doping structure is introduced in the strained GaAs layer of a pho tocathode in order to realize a highly polarized electron source. The grade d doping produces an internal electric field which moves photoexcited elect rons toward the surface. Spin relaxation time and life time of photoexcited electrons in the graded doping GaAs layer are measured by the time-resolve d photoluminescence method. The spin relaxation due to electron-hole scatte ring is suppressed by the transfer of photoexcited electrons toward the sur face in a short time.