Carrier transport affected by Γ-X transfer in type-I GaAs/AlAs superlattices

We studied how T-X transfer affects electron transport in type-I GaAs/AlAs semiconductor superlattices under an electric field,Gamma to X transfer was found to degrade the sweep out of carriers, while X to Gamma resonance was observed to promote it. An anomalously delayed photocurrent was observed under ultrashort optical pulse excitation. This phenomenon is explained by a switch of the electron transport path from Gamma-Gamma to Gamma-X-Gamma-X, caused by a change in the subband alignment between the second Gamma state (Gamma(2)) in the well and the X-z ground state (X-1) in the adjacent barrier by the electric field. The delayed photocurrent could be reproduced by a simple simulation while considering the above carrier transport paths. These results provide evidence that Gamma-X-Gamma real-space transfer considerably affects carrier transport even in type-I superlattices under an electric field.