Effect of non-square potential profile on three subband electron mobility in AlGaAs quantum well structures

Abstract

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 × 1018 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.