The role of interface quality in resonant tunneling between transverse X-states in GaAs/AlAs double barrier structures pressurised beyond the type II transition

We examine in detail the first high pressure resonance related to tunneling between the lowest transverse X-state in each AlAs layer, of GaAs/AlAs 'double barrier' structures with equal AlAs thicknesses grown by Molecular Beam Epitaxy (MBE) calibrated using Reflection High Energy Electron Diffraction (RHEED), and we compare the results with previously reported measurements on Metalorganic Vapour Phase Epitaxy (MOVPE) grown structures. The resonance, which does not conserve in-plane momentum, is much sharper and more asymmetric between forward and reverse biases in MBE structures, and the sense of the asymmetry in these structures, which can be as large as 6:1, always appears to be the same relative to the polarity of the substrate. At the same time momentum conserving resonances, such as the ambient pressure Γ-resonance, remain highly symmetric in all samples, confirming that the two AlAs layers have closely equal thicknesses. The lack of in-plane momentum conservation results in great sensitivity to differences in roughness at the two types of interface (AlAs grown on GaAs or GaAs grown on AlAs), and to differences in roughness related to the method of growth (MBE and MOVPE). © 1995