Interplay of disorder and tunneling in coupled quantum well structures – tuning the intersubband line shape by an electric field

We theoretically investigate the disorder-induced localization of electrons and the broadening of intersubband (IS) absorption lines in asymmetric double-well (ADW) structures with three bound subbands. As a function of an electric field applied in growth direction, the two-peak IS spectrum of the system is calculated from realistic, in-plane localized single-particle states. The simultaneous monitoring of, both, intra- and inter-well transitions reveals the importance of spatial correlations for the inhomogenous line broadening effect. We generally find that the inter-well IS peak is considerably broader than the intra-well line. This can be traced back to a suppression of IS correlations in the case of a spatially indirect transition, where the initial and final subband probe different regions of the fluctuating potential landscape. At a certain electric field, however, the excited subbands form molecule-like states, spreading over both quantum wells, and the IS peaks take on comparable widths.