OPTICAL-PROPERTIES AND THERMAL TRANSPORT OF CARRIERS IN (ZN,CD)SE-ZNSE HETEROSTRUCTURES

We report a detailed optical study of ZnSe-based graded index separate confinement heterostructures. These structures were grown by metalorg anic vapor phase epitaxy and are composed of either one or two Zn0.79C d0.21Se central well(s) embedded between two ZnCdSe barriers which cad mium composition varies linearly from 5% near the wells to 0% at the e nd of the barriers. 2K photoreflectance and reflectivity experiments a llow the observation of excitonic transitions involving the third elec tron and heavy hole confined states. The temperature dependence of the photoluminescence lines under in-well resonant excitation conditions (E(exc) = 2.661 eV) shows that the thermal quenching of the photolumin escence line is ruled by nonradiative recombinations on defects locali zed at the heterointerfaces at low temperature and by the thermal esca pe of the minority carriers at higher temperatures. Under above-barrie r excitation conditions (E(exc) = 3.814 eV), the temperature dependenc e of the photoluminescence line from the well shows a strong influence of the mechanism of diffusion of the carriers from the barriers to th e well.