Effect of Non-Square Potential Profile on Three Subband Electron Mobility in AlGaAs Quantum Well Structures

This work analyses the effect of the non-square structure potentials, such as V-shaped (V), parabolic (P), cubic (C), semi-V (SV), semi-parabolic (SP), and semi-cubic (SC) on the low temperature electron mobility ( μ ) as a function of doping concentrations ( N d = 0.1 to 3.0 × 10 18 cm −3 ) in modulation δ -doped quantum well (QW) structures. We calculate μ by adopting screened ionized impurity ( ii- ) and alloy disorder ( al- ) scatterings. We consider higher subband occupancy up to three and show that the intersubband effects influence the screened scattering potentials differently, such that μ ii increases while μ al decreases, leading to nonlinear enhancement of μ . Further, there are sudden drops in μ , near the transition of occupation of subbands due to the intersubband effects, and the magnitude of the drop is reduced at the third subband occupancy. The number of occupied subbands ( nos ), for the considered range of N d , differs with NSQW structures, e.g., nos = 3 in the case of VQW, CQW, and PQW, nos = 2 in SCQW and SPQW, and nos = 1, in SVQW structures. Interestingly, in VQW, the occupation of the second subband starts at a higher N d , compared to CQW and PQW, while, the third subband occupancy shows an opposite trend. Furthermore, the dissimilarity in electron charge distributions in the NSQW structures influences the ii -scattering potential differently, causing μ ii (VQW) > μ ii (PQW) > μ ii (CQW), while for al- scattering the order of μ al reverses.