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 angstrom thick InGaAs/GaAs quantum well (QW). We could resolve both the E1 - H-1 and E2 - H-2 excitonic features, up to L(D) = 80 angstrom. We show that both energy shifts agree well with a simple model which assumes a Fick's law diffusion, 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 diffusion proceeds but, also, a diffusion of the lattice constituents in the plane of the well. This in-plane diffusion smoothes the interfaces and reduces the monolayer well width fluctuations.