Effect of inhomogeneous broadening on optical properties of excitons in quantum wells

The effect of inhomogeneous broadening on exciton-light coupling in quantum wells (QW’s) is studied by a semiclassical model, in which the exciton resonance frequency is assumed to have a Gaussian distribution. The presence of disorder may be observed in absorption, but not in reflectivity spectra. The integrated absorption of light in single and multiple QW’s is nonzero only in the presence of a finite damping and increases with enhancement of either homogeneous or inhomogeneous broadening: only when broadening is larger than the exciton radiative width does the integrated absorption attain the saturation value expected from the exciton oscillator strength and the number of QW’s. This behavior is similar to that of exciton-polariton absorption in bulk semiconductors, 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 bulk, in general, disorder produces a decrease of the period of oscillations in the time-resolved transmission and yields a faster decay of the signal. However, inhomogeneous broadening is also found to lead to beatings 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, may be observed in high-quality samples.