EXCITON OSCILLATOR STRENGTH IN QUANTUM-WELLS - FROM LOCALIZED TO FREE RESONANT STATES

A model is proposed which describes the evolution of exciton oscillator strength in a quantum well with lateral potential fluctuations. Four different types of exciton lateral confinements are evidenced: (type A) the strongly localized quantum-dot-like states, (type B) excitons localized as whole particles in long-scale potential fluctuations, (type C) free excitons at the mobility edge, and (type D) free-exciton resonances above the mobility edge. This model provides the continuous changes of the calculated oscillator strength during the transition between these localization regimes. We show that the inhomogeneous broadening of the quantum-well exciton line in the absorption spectra should be rather symmetric, while the higher energy wings of the spectra are caused by the resonances in the continuum of free states.