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-q uantum-well (MQW) structure with well-width fluctuations, and in an in ternal-reflection configuration, the linear optical intersubband absor ption spectra including peak positions and line shapes are strongly de pendent 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 electrom agnetic coupling among QW's, and consequently leads to a significant m odification of the optical-absorption spectra. By varying the intersub band relaxation time, we find that the local-field effect may substant ially reduce the linewidth broadening arising from the conduction band nonparabolicity effect for a highly doped MQW system. This is in agre ement with a previous prediction for a single QW. In addition, the pre sent nonlocal theory is compared with the effective-medium theory (EMT ). Our calculations show that the nonlocal effect in the optical respo nse of QW's gives rise to a notable blueshift of the absorption peak c ompared to the results in the EMT approach. When the QW number is vari ed, the line shapes predicted from the two theories are also somewhat different.