OPTICAL SPECTROSCOPY IN (ZN,CD)SE-ZNSE GRADED-INDEX SEPARATE-CONFINEMENT HETEROSTRUCTURES

We report a detailed examination of the electronic structure and of th e thermal transport in a graded-index separate-confinement heterostruc ture based on (Zn,Cd)Se wide-band-gap II-VI semiconductors, and design ed in the view of a blue-green light emission device. The band offsets and strain state of the heterostructure are obtained from 2-K photore flectance measurements. The temperature dependence of the photolumines cence spectra taken both in a resonant in-well excitation condition an d in an above-barrier excitation condition has enabled us to quantify the mechanisms responsible for the photoluminescence thermal quenching . This has been done in the context of a sophisticated model that incl udes several nonradiative processes. In the 10-70 K temperature range, the photoluminescence intensity is found to be ruled by a nonradiativ e detrapping towards interfacial defects, whilst the thermal escape ef fect is responsible for the photoluminescence quenching at higher temp eratures. In the case of an above barrier excitation condition, the co ntribution of the carriers diffusion from the barriers to the well lea ds to an increase of the quantum-well photoluminescence, the intensity of which exhibits a maximum around 50 K.