Enhancement of 2D -> 2D tunneling by Gamma-X-Z mixing in GaAs/AlAs resonant tunneling structures at high pressure

We have investigated the 2D --> 2D resonant tunneling in coupled X-band dou ble quantum well structures, which can be achieved in GaAs/AlAs heterostruc tures by using high hydrostatic pressure. Until recently, there has been cl ear observation of 2D --> 2D resonant tunneling between confined transverse X-X,X-Y states but not between longitudinal X-Z states. In this paper, we demonstrate the existence of such resonant tunneling in samples with very t hin well and barrier layers. The existence of detectable 2D --> 2D resonant tunneling between X-Z states, even in a structure with a barrier thickness of 40 Angstrom, is striking. However, by modelling the transport in terms of quantum beats between symmetric and anti-symmetric double well states, w e show that Gamma-X-Z mixing can produce enhancements of up to approximate to 10(2).