HOLE STATES IN GAAS ALAS DOUBLE-BARRIER STRUCTURES AND MULTIPLE-QUANTUM WELLS

We present a microscopic pseudopotential-based calculation including s pin-orbit interaction for hole tunnelling in finite GaAsAlAs multiple quantum wells. We have examined the light hole-heavy hole (mixing) in a GaAs/AlAs double-barrier structure and how the resonant states evol ve into minibands in multiple quantum well structures. We find new fea tures in the transmission characteristics which could not have been ob tained from simple models. The double-barrier structure results show s trong light-hole-heavy-hole mixing and quantum interference behaviour characterized by transmission 'antiresonances' as well as the usual re sonances. More striking are the results for multiple quantum wells, wh ere there is a loss in number of transmission resonant states for the heavy-hole minibands. For thicker barriers the heavy-hole miniband col lapses and only a single resonant state is left, while the light-hole minibands remain intact. We interpret the lost resonances as being res onant contact interface states. This anomalous behaviour of formation of a contact interface state instead of a heavy-hole miniband is argue d to be due to strong interface light-hole-heavy-hole mixing and the f act that for all but the thinnest AlAs barriers, only the evanescent l ight-hole barrier channel mediates the interwell coupling. This anomal ous behaviour, which could not have been predicted from a calculation on an infinite superlattice, has consequences for transport measuremen ts.