Modulation of electron transport and quantum lifetimes in symmetric and asymmetric AlGaAs/InGaAs double quantum well structures

Abstract

The low-temperature electron transport (τ t ) and quantum (τ q ) lifetimes are modulated as a function of applied electric field (F) in Al0.3Ga0.7As/In0.15Ga0.85As-based symmetric and asymmetric double quantum well structures by considering ionized impurity, alloy disorder and interface roughness scatterings. The asymmetry in the structure potential is achieved through differences in the well widths, i.e. W w1 ≠ W w2. We show that in a symmetric structure (W w1 = W w2 = 120 Å) resonance of subband states (RSS) occurs at F = F rss = 0, whereas in asymmetric structures [(W w1, W w2) = (90 Å, 150 Å) and (W w1, W w2) = (150 Å, 90 Å)], the RSS is shifted and occurs at |F rss| = 16.4 kV cm−1. The symmetric and antisymmetric nature of the subband wave functions at their corresponding F rss makes τ t a minimum and this increases with change in F during multisubband occupancy. However, the absence of the factor 1 – cosθ in the quantum lifetime makes τ q one order less than the magnitude of τ t , but τ q shows a maximum at the corresponding F rss and decreases with change in F. The above changes in τ t and τ q with F make their ratio τ t /τ q maximum at the transition of subband states.