Optoelectronics of semiconductor superlattices

We discuss the linear and nonlinear optical properties of ideal and disordered semiconductor superlattices and their modification due to homogeneous electric fields applied along the growth direction. The disorder under consideration is caused by monolayer fluctuations of the well widths and the finite number of wells in short-period superlattices. We show how to derive the multiband semiconductor Bloch equations used for the theoretical modeling of these systems. For ideal superlattices we investigate the field dependence of linear absorption and the density dependent absorption. The dephasing due to electron-phonon interaction of the THz radiation emitted by Bloch-oscillating carriers is shown to be strongly field dependent. It is demonstrated that the THz-signals can be dominated by either free-carrier motion or beating between excitonic resonances, depending on the excitation conditions. Afterwards the influence of the disorder on the linear absorption, the THz emission and four-wave-mixing signals is discussed. For the linear absorption we show that its influence on the low energy side can be much weaker than on structures above the band edge. Here, we also present results for type II and doping superlattices. In these systems locally indirect excitons are shown to occur which differ in their field dependent behaviour from the direct excitons in type I superlattices. For THz radiation the disorder is shown to lead to a dephasing rate that is linear in the applied electric field. Finally, four-wave-mixing signals for some idealized finite superlattices are used to discuss the complex nature of disorder-induced dephasing.