Subband selective disorder in a quasi-2D system and its effect on the intersubband spectrum

We investigate theoretically the intersubband (IS) absorption spectra of a quantum well with a sub-monolayer of barrier material inserted at the well center zc. This “perturbation layer” creates a random lateral potential modulation with different fluctuation amplitudes Δm for the ground (m=0) and first excited (m=1) subband. In the unbiased system, the 0-electrons become in-plane localized by the perturbation (Δ0>0), while the excited subband remains unaffected (Δ1=0), due to the node of its wave function at zc. In this case of selective disorder our calculated IS spectra show at low carrier density a broad peak, reflecting the View the MathML source-spectrum of 0-electron states, in-plane localized in the “void areas” of the perturbation layer. For higher densities, a second, sharper peak occurs at lower energies, due to occupation of extended states. By applying a longitudinal electric field, the fluctuation amplitudes Δm of the two subbands can be continuously varied, up to the point where Δ1=Δ0 (case of correlated disorder). The corresponding IS spectra gradually change to a single, very narrow line with an only weak dependence of position and width on carrier density.