EVIDENCE FOR GAMMA-CHI TRANSPORT IN TYPE-I GAAS ALAS SEMICONDUCTOR SUPERLATTICES/

We report the first evidence that the Gamma-X transfer mechanism plays a significant role in carrier transport in type-I semiconductor super lattices under an electric field. An anomalously delayed photocurrent was observed in a GaAs/AlAs type-I superlattice under ultrashort optic al pulse excitation. This phenomenon can be explained by a switch of t he electron transport path from Gamma-Gamma to Gamma-X-Gamma-X, caused by an electric-field induced change of the subband alignment of the s econd Gamma state (Gamma 2) in the well and the X1 state in the adjace nt barrier.