THE ROLE OF INTERFACE QUALITY IN RESONANT-TUNNELING BETWEEN TRANSVERSE X-STATES IN GAAS ALAS DOUBLE-BARRIER STRUCTURES PRESSURIZED BEYOND THE TYPE-II TRANSITION/

We examine in detail the first high pressure resonance related to tunn eling between the lowest transverse X-state in each AlAs layer, of GaA s/AlAs 'double barrier' structures with equal AlAs thicknesses grown b y Molecular Beam Epitaxy (MBE) calibrated using Reflection High Energy Electron Diffraction (RHEED), and we compare the results with previou sly reported measurements on Metalorganic Vapour Phase Epitaxy (MOVPE) grown structures. The resonance, which does not conserve in-plane mom entum, is much sharper and more asymmetric between forward and reverse biases in MBE structures, and the sense of the asymmetry in these str uctures, which can be as large as 6:1, always appears to be the same r elative to the polarity of the substrate. At the same time momentum co nserving resonances, such as the ambient pressure Gamma-resonance, rem ain highly symmetric in all samples, confirming that the two AlAs laye rs have closely equal thicknesses. The lack of in-plane momentum conse rvation results in great sensitivity to differences in roughness at th e two types of interface (AlAs grown on GaAs or GaAs grown on AlAs), a nd to differences in roughness related to the method of growth (MBE an d MOVPE).