Carrier transport affected byΓ−Xtransfer in type-I GaAs/AlAs superlattices

Abstract

We studied how $\ensuremath{\Gamma}\ensuremath{-}X$ transfer affects electron transport in type-I GaAs/AlAs semiconductor superlattices under an electric field. $\ensuremath{\Gamma}$ to X transfer was found to degrade the sweep out of carriers, while X to $\ensuremath{\Gamma}$ 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 $\ensuremath{\Gamma}\ensuremath{-}\ensuremath{\Gamma}$ to $\ensuremath{\Gamma}\ensuremath{-}X\ensuremath{-}\ensuremath{\Gamma}\ensuremath{-}X,$ caused by a change in the subband alignment between the second $\ensuremath{\Gamma}$ state $({\ensuremath{\Gamma}}_{2})$ 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 $\ensuremath{\Gamma}\ensuremath{-}X\ensuremath{-}\ensuremath{\Gamma}$ real-space transfer considerably affects carrier transport even in type-I superlattices under an electric field.