Effect of thermal diffusion on the excitonic reflectivity spectra of InGaAs/GaAs quantum wells

We have investigated the effect of intermixing on the excitonic reflectivity spectra of a 100 Å thick InGaAs/GaAs quantum well (QW). We could resolve both the El - Hl and E2 - H2 excitonic features, up to LD = 80 Å. We show that both energy shifts agree well with a simple mode1 which assumes a Fick's law diffision, with a diffusion coefficient that is independent of the concentration of the cationic species. Next, considering the change (improvement) in signal to : noise ratio versus thermal annealing, we suggest that, in our samples, we not only get a broadening of the quantum well as the diffision proceeds but, also, a diffision of the lattice constituents in the plane of the well. This in-plane diffision smoothes the interfaces and reduces the monolayer well width fluctuations