EFFECT OF INHOMOGENEOUS BROADENING ON OPTICAL-PROPERTIES OF EXCITONS IN QUANTUM-WELLS

The effect of inhomogeneous broadening oh exciton-light coupling in qu antum wells (QW's) is studied by a semiclassical model, in which the e xciton resonance frequency is assumed to have a Gaussian distribution. The presence of disorder may be observed in absorption, but not in re flectivity spectra. The integrated absorption of light in single and m ultiple QW's is nonzero only in the presence of a finite damping and i ncreases with enhancement of either homogeneous or inhomogeneous broad ening: only when broadening is larger than the exciton radiative width does the integrated absorption attain the saturation value expected f rom the exciton oscillator strength and the number of QW's. This behav ior is similar to that of exciton-polariton absorption in bulk semicon ductors, but unlike the bulk case it is not due to spatial dispersion. For multiple QW's, QW's in a microcavity and in a thick film of bulls , in general, disorder produces a decrease of the period of oscillatio ns in the time-resolved transmission and yields a faster decay of the signal. However, inhomogeneous broadening is also found to lead to bea tings in the time-resolved transmission or reflection of light from a single QW: the oscillations, which originate from interference between upper and lower wings of the exciton distribution, maybe observed in high-quality samples. [S0163-1829(98)06507-2].