ULTRAFAST ELECTRON-TRANSFER IN TYPE-II GAAS ALAS SUPERLATTICES BY FEMTOSECOND LUMINESCENCE/

Electron transfer from GaAs wells (Gamma wavefunctions) to AlAs barrie rs (X wavefunctions) in GaAs / AlAs type II superlattices has been stu died by time resolved luminescence with femtosecond resolution. Transf er times can be as short as 140 fs for narrow wells and as long as 25 ps for the widest wells. They do not depend appreciably on the barrier thickness. We discuss the possible contribution to the transfer mecha nism of state mixing, intervalley scattering and Frolich interaction. Our measurement favors phonon assisted, intervalley type scattering, m odified by the overlap of the different wavefunctions.