Hole states in GaAs/AlAs double-barrier structures and multiple quantum wells

Abstract

We present a microscopic pseudopotential-based calculation including spin-orbit interaction for hole tunnelling in finite GaAs*AlAs multiple quantum wells. We have examined the light hole-heavy hole (mixing) in a GaAs/AlAs double-barrier structure and how the resonant states evolve into minibands in multiple quantum well structures. We find new features in the transmission characteristics which could not have been obtained from simple models. The double-barrier structure results show strong light-hole-heavy-hole mixing and quantum interference behaviour characterized by transmission 'antiresonances' as well as the usual resonances. More striking are the results for multiple quantum wells, where there is a loss in number of transmission resonant states for the heavy-hole minibands. For thicker barriers the heavy-hole miniband collapses and only a single resonant state is left, while the light-hole minibands remain intact. We interpret the lost resonances as being resonant contact interface states. This anomalous behaviour of formation of a contact interface state instead of a heavy-hole miniband is argued to be due to strong interface light-hole-heavy-hole mixing and the fact that for all but the thinnest AlAs barriers, only the evanescent light-hole barrier channel mediates the interwell coupling. This anomalous behaviour, which could not have been predicted from a calculation on an infinite superlattice, has consequences for transport measurements.