Radiative interaction and disorder effect in the linear optical response of a multiple-quantum-well structure

Using a nonlocal local-field formalism, we show that, for a multiple-quantum-well (MQW) structure with well-width fluctuations, and in an internal-reflection configuration, the linear optical intersubband absorption spectra including peak positions and line shapes are strongly dependent on the number of quantum wells (QW's) in the structure and of the spatial distribution of the QW's. It is also demonstrated that an inclusion of the barrier-medium–vacuum interface enhances the electromagnetic coupling among QW's, and consequently leads to a significant modification of the optical-absorption spectra. By varying the intersubband relaxation time, we find that the local-field effect may substantially reduce the linewidth broadening arising from the conduction band nonparabolicity effect for a highly doped MQW system. This is in agreement with a previous prediction for a single QW. In addition, the present nonlocal theory is compared with the effective-medium theory (EMT). Our calculations show that the nonlocal effect in the optical response of QW's gives rise to a notable blueshift of the absorption peak compared to the results in the EMT approach. When the QW number is varied, the line shapes predicted from the two theories are also somewhat different.