Enhancement of multisubband electron mobility in square-parabolic asymmetric double quantum well structure

We show that higher multisubband electron mobility μ can be achieved in AlxGa1-xAs based hybrid type square-parabolic asymmetric double quantum well (HDQW) compared to that of the symmetric square double quantum well (SDQW) and parabolic double quantum well (PDQW) structures. We show that μ(HDQW) > μ(PDQW) > μ(SDQW). This trend in the enhancement of μ is mostly governed by the change in the ionized impurity scattering potential. The mobility of the HDQW can be enhanced by increasing the well width and also the curvature of the parabolic potential. In addition, μ(HDQW) becomes larger when the parabolic well lies towards the substrate side compared to that of the surface side due to the reduced effect of the interface roughness scattering. The mobility also increases with increase in the surface electron density Ns. The enhancement of μ in HDQW is because of the reduction of the intersubband scattering rate matrix elements due to the asymmetric distribution of the subband wave functions. Our results can be utilized to develop asymmetric double quantum well field effect transistor.