Density-dependent intersubband absorption in strongly disordered systems

We study theoretically the intersubband (IS) absorption spectrum of electrons in a center-doped quantum well (QW) as a function of the carrier density. Besides the subband quantization in z direction, the wave functions of the electrons, being directly exposed to the charged dopands, become disorder localized in the layer plane. For each set of random impurity configurations, the corresponding spectrum of quantum states is computed with a self-consistent density-functional approach, thus, taking into account the disorder and nonlinear static screening effects in a realistic way. On the basis of these effective single-particle states, we then include dynamic many-body effects (depolarization and dynamic exchange corrections) by applying and extending our recently developed theory of resonant screening in the localization regime. We analyze the relevance of the various many-body effects and find that at higher electron densities the direct static Hartree and the depolarization contributions dominate over the exchange effects. Dynamic Coulomb interactions qualitatively change the IS absorption spectrum of the statically screened electron gas, however, do not lead to a spectral narrowing in this system. A small variation of the $\delta n$-layer position within the QW affects the relative disorder strength of the two subbands and causes dramatic changes of the spectral shape and width. Our model and results are suitable for a direct comparison with experimental data.