Resonant tunneling between transverse X states in GaAs/AlAs double-barrier structures under elevated hydrostatic pressure

We present a model to describe the mechanisms involved in tunneling between the quasiconfined X subbands of the AlAs layers in GaAs/AlAs double-barrier structures at pressures up to the type-II transition. The model involves self-consistent Schr\"odinger-Poisson calculation of the potential profiles within the device for a given relative alignment between the two X-like quantum wells, and thus allows prediction of the bias positions at which certain resonant tunneling processes will occur. By systematic variation of the parameters involved, in particular the charge distribution between the two AlAs layers, these predictions have been fitted to the measured vertical transport characteristics of a series of samples of different AlAs layer width. In the cases of those samples with X ground states that are transverse in nature, very good agreement has been obtained. The level of insight afforded by the model opens up alternative methods for the determination of important band-structure parameters, such as the light effective mass of the X minima in AlAs, and the ΓGaAs-XAlAs conduction-band offset. It also proves to be an extremely sensitive probe of the degree of symmetry between the AlAs layer widths of near-symmetric devices, and we are thus able to measure an asymmetry of around one monolayer in each of our devices. This explains entirely the asymmetry exhibited by the low bias Xₜ(1)→Xₜ(1) resonances of some nominally symmetric double-barrier structures, which has been a source of some debate in recent years.