Enhancement of electron mobility in GaAs/AlxGa1-xAs square-parabolic double quantum well HEMT structure

Abstract

We show that the enhancement of electron mobility μ as function of well width w can be achieved in a GaAs/AlxGa1-xAs square-parabolic double quantum well (SPDQW) high electron mobility transistor (HEMT) structure. We consider the structures, in which one of the square well lies towards the substrate (SPDQW), and in another towards the surface (PSDQW). We also consider a symmetric square double quantum well (SDQW). In all the structures the wells are of equal width w and the side barriers are symmetrically delta doped with Si. We calculate μ by considering ionized impurity (ii-), alloy disorder (al-) and interface roughness (ir-) scatterings. We show that for lower w, single subband is occupied and μ is governed by ir-scattering. Near the transition from single subband to double subband occupancy, the drop in μ occurs and thereafter μ is governed by ii-scattering mediated by intersubband effects. We analyze the effect of coupling of subband wave functions through the central barrier width b and change in the potential profile through an external electric field F on μ. We show that for all values of w, μ (PSDQW) > μ (SPDQW) > μ (SDQW). We also calculate μ for a parabolic double quantum well (PDQW) and analyze the effect of change in the curvature of the parabolic potential which shows that μ (SPDQW) > μ (PDQW) at larger well widths. Our results can be utilized for the enhancement of the hybrid quantum well HEMT devices.