Coupling of infrared radiation to intersubband transitions in multiple quantum wells: The effective-medium approach

The coupling of infrared radiation to intersubband excitations in multiple-quantum-well structures is discussed theoretically, employing the effective-medium approach. In contrast with previous papers, nonlocal effects in the intersubband optical response of quasi-two-dimensional electrons are taken into account. The transmission and total internal reflection geometries are considered. Special attention is paid to effects induced by (i) multiple reflections in the multiple-quantum-well structure itself, and (ii) the standing-wave effect connected with background phase-matched interferences. The results obtained indicate that the standing-wave effect plays an important role only in the case of thin structures. It can be taken into account by an appropriate modification of Beer’s law. Multiple reflections substantially modify the intersubband absorption line shape of structures with a large number of quantum wells and near grazing incidence. A correct description of this modification must take into account even small differences between the dielectric constants of the well and barrier materials.