We report on optical and magneto-optical studies of a ZnCdSe-ZnSe strained layer superlattice. This structure was grown by metal-organic vapour phase epitaxy (MOVPE) and consisted of 40 periods of 72 Angstrom ZnCdSe layer and 49 Angstrom ZnSe layer with cadmium composition equal to 4%. Photoluminescence, reflectivity and magnetocircular dichroism experiments at 2 K were used to identify e(1)-hh(1) and e(1)-lh(1) excitonic transitions. By comparing these experimental transitions with the calculated ones, we have determined the valence and the conduction band offsets. In these calculations, we have included values of the binding energies related to the different transitions. These binding energies are calculated within the formalism of fractional dimensional space. Zeeman splitting of \+/-3/2, +/-1/2] and \+/-1/2, -/+ 1/2] transitions are calculated at 5.5 T and the corresponding effective g-values g(3/2) and g(1/2) are deduced. (C) 1997 Elsevier Science S.A.

We report a detailed optical study of ZnSe-based graded index separate confinement heterostructures. These structures were grown by metalorganic vapor phase epitaxy and are composed of either one or two Zn0.79Cd0.21Se central well(s) embedded between two ZnCdSe barriers which cadmium composition varies linearly from 5% near the wells to 0% at the end of the barriers. 2K photoreflectance and reflectivity experiments allow the observation of excitonic transitions involving the third electron 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 photoluminescence line is ruled by nonradiative recombinations on defects localized at the heterointerfaces at low temperature and by the thermal escape of the minority carriers at higher temperatures. Under above-barrier excitation conditions (E(exc) = 3.814 eV), the temperature dependence of the photoluminescence line from the well shows a strong influence of the mechanism of diffusion of the carriers from the barriers to the well.

We report on the growth of ZnS-ZnSe superlattices by MOVPE. These superlattices were characterized by optical spectroscopy. We have calculated the exciton binding energy in ZnSe-ZnS quantum wells in the context of the variational approach using models of varying degree of sophistication.

Graded index-separate confinement heterostructures (GRIN-SCH) based on ZnCdSe and ZnSe wide band gap semiconductors have been grown by low pressure MOVPE on (100) GaAs substrates. First, we have paid attention to the growth of thick ZnCdSe layers. A first study is carried out using selenium hydride, dimethyl cadmium and two dimethylzinc adducts as Se, Cd and Zn precursor respectively. This combination leads to intense prereactions and poor layer morphology. To limit this problem we have then used the tetrahydrothiophene:dimethylcadmium adduct. GRIN-SCH structures grown using the two Cd metalorganics are studied using photoluminescence. We have made a detailed study on the influence of the temperature on the carrier trapping and detrapping in the structures.

The successful growth of MgS epitaxial layers with the MOVPE technique is reported. The samples were grown on GaAs substrates in a classical horizontal reactor, using bis(methylcyclopentadienyl) magnesium and H2S as precursors. The zincblende structure of MgS layers is evidenced by careful X-ray diffraction analysis. The lattice constant is found to be about 5.66 Angstrom. The influence of the growth temperature on the morphology and quality of the layers is studied in detail.

We report a detailed examination of the electronic structure and of the thermal transport in a graded-index separate-confinement heterostructure based on (Zn,Cd)Se wide-band-gap II-VI semiconductors, and designed in the view of a blue-green light emission device. The band offsets and strain state of the heterostructure are obtained from 2-K photoreflectance measurements. The temperature dependence of the photoluminescence spectra taken both in a resonant in-well excitation condition and 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 includes several nonradiative processes. In the 10-70 K temperature range, the photoluminescence intensity is found to be ruled by a nonradiative detrapping towards interfacial defects, whilst the thermal escape effect is responsible for the photoluminescence quenching at higher temperatures. In the case of an above barrier excitation condition, the contribution of the carriers diffusion from the barriers to the well leads to an increase of the quantum-well photoluminescence, the intensity of which exhibits a maximum around 50 K.

An investigation of the reflectivity and photoluminescence spectra of 40-period Zn1-xCdxSe-ZnSe strained layer superlattices is reported. Superlattices with cadmium composition between 3% and 10% were grown by metal organic vapour phase epitaxy. The well and barrier widths were varied in order to study the tunnelling effect in the superlattices. This effect was shown to be large not only for the excited states (e(2)hh(2) transitions for the 10% cadmium composition) but also for e(1)hh(1) transitions despite the large heavy hole effective mass. The band discontinuities were determined by calculating the transition energies within the envelope function framework generalized to strained layers. It was found that for all superlattices the mechanical state is pseudomorphic and that the heavy hole band offset is 32% of the energy difference of the strained band gaps. The binding energies and the oscillator strengths of the various excitonic transitions were calculated within the formalism of fractional-dimensional space and compared with variational calculations reported in the literature.