Optical spectroscopy study of the phase of the reflection coefficient of a single quantum well in the exciton resonance region

Using reflectivity and thermally detected optical absorption spectra of a (In,Ga)As/GaAs single quantum well (QW) sample we have restored the complex amplitude reflection coefficient of the QW in the vicinity of the exciton resonance region. Our method has allowed experimental determination of the phase of the reflection coefficient of a QW. Knowing this phase we were able to distinguish between inhomogeneous and homogeneous contributions to the exciton broadening. A model based on the nonlocal dielectric response theory and assuming the in-plane component of the wave vector of light to be conserved has provided an excellent agreement with the data. The time-resolved reflection spectra of a single QW have been obtained by the numerical Fourier transform of the complex reflection coefficient of the QW. They have shown pronounced oscillations caused by an inhomogeneous broadening of the single exciton resonance.