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.

We report the observation of discrete modes in the upper branch of the exciton-polariton. In micrometer thick ZnSe epilayers grown on GaAs substrates by metal organic vapour phase epitaxy we have studied the evolution of the reflectivity spectra as a function of the thickness of the deposited ZnSe layers. For layer thickness in the range of a micron we observe reflectance oscillations that we interpret as due to Fabry-Perot modes in the upper branch of the polariton. This observation is possible due to the large exciton binding energy in ZnSe and the subsequent large energy extension of this branch. The amplitude of these oscillations and their energy splitting decrease with increasing thickness of the epilayer. They could no longer be observed for thickness larger than 4.5 mu m. The effect is analyzed in the context of a semiclassical approach using a non-local description of the dielectric constant, combined with results previously obtained in thin layers of bulk CdSe and CuCl.

We investigated the evolution; of the relative oscillator strengths of the A, B, and C excitons in alpha-GaN epilayers grown along the [0001] direction an sapphire, 6HSiC, and ZnO substrates by metalorganic vapor phase epitaxy and molecular-beam epitaxy. A universal model was found to account for the observed spectroscopic features regardless of the substrate employ-ed. In addition, we found that, due to the small value of the spin-orbit interaction compared to the stress-induced modifications of the interlevel splitting, C and B Lines may undergo a strain-induced exchange of their oscillator strengths when strain field in the epilayers varies from biaxial tension towards biaxial compression. Moreover, we can account for the strain-induced distribution of radiative recombination rates in high-quality GaN epilayers.

The effect of the built-in biaxial stress on the E(2) and A(1) (LO) q = 0 phonon modes of wurtzite GaN layers deposited by Metal Organic Vapor Phase Epitaxy on (0001) direction on sapphire substrates is studied by Raman spectroscopy. Shifts in phonon frequencies are measured, which we correlate to the residual strain fields in the epilayers. Using stress calibration measurements taken from reflectance data, the biaxial pressure coefficients of mode frequencies are determined and used to calculate the corresponding deformation potentials.

We present a joint study of the band offsets and exciton binding energies in Zn1-xCdxSe-ZnSe quantum wells grown by metal-organic vapor-phase epitaxy with cadmium composition ranging up to 22%. The optical-spectroscopy data presented here are the wavelength derivative of the 2-K reflectance. The strained band-gap difference is divided as follows: the heavy-hole valence-band share deduced from the calculation is 32±1%; the remainder is allotted to the electron conduction band. The exciton binding energy has been calculated within the context of two methods: first, we propose a variational calculation using an exciton wave function written as the product of the envelope-function solutions of the square-well problem with a hydrogenlike two-parameter trial function. Second, as the light-hole potential is marginally type I, we lay out a more sophisticated computation based on a self-consistent variational approach that gives both the exciton binding energies and the self-consistent light-hole densities of probability. We compare the full information given by these two approaches.

We present a detailed examination of the optical properties and electronic structure taken from photoreflectance and photoluminescence data collected on a series of short-period ZnS-ZnSe superlattices grown by low pressure metalorganic vapor phase epitaxy. We studied the band offset problem and calculated the exciton binding energy using several variational models. The temperature dependence of the photoluminescence properties of these superlattices was analyzed in the context of a model which includes the influence of the interfacial disorder.

A series of In0.14Ga0.86As-GaAs quantum well structures have been grown by metal organic chemical vapor deposition (MOCVD). The measured dependence of photoluminescence (PL) energies on well width is compared with calculation. By the energy shift, line width and intensity change of PL spectroscopy, critical layer thickness has been identified. The critical layer thickness obtained for MOCVD grown material was found in agreement with theoretical value, but is smaller than molecular beam epitaxy grown ones.