Nonlinear electron transport mobility in asymmetric wide quantum well structure

Abstract

The nonlinearity of multisubband electron mobility µ in a GaAs/AlxGa1−xAs wide quantum well structure is studied by varying the well width w and doping concentration Ndb (Ndt) lying in the bottom (top) barrier. The electrons diffuse into the well and accumulate near the interfaces forming two sheets of coupled two dimensional electron gases equivalent to a double quantum well structure. We show that interchange of doping concentrations Ndb and Ndt lead to the enhancement of µ as a function of w as long as Ndt > Ndb, even though the surface electron density remains unaltered. Further, keeping Ndb unchanged, variation of Ndt leads to nonlinearity in µ near the resonance of subband states at Ndt = Ndb at which the subband energy levels exhibit anticrossing. The variation of µ becomes prominent by increasing the well width and resonant doping concentration. The nonlinearity in µ is mostly because of the change in the interface roughness scattering potential through intersubband effects due to the substantial changes in the distributions of the subband wave functions around resonance. Our results of nonmonotonic variation of µ can be utilized for low temperature coupled quantum well devices.