Gallium nitride has been grown using low pressure MOCVD and ammonia and triethylgallium as precursors. A wide range of operating conditions have been investigated : the temperature was varied between 950 and 1050 degrees C and the V/III molar ratio was changed from 1000 to 10000. The influence of the growth parameters on the optical quality is reported here. For optimized epilayers, low temperature reflectance data have been taken and analyzed in the context of a multi-polariton model using a non local description of the dielectric constant The energy positions of the resonances have been analyzed in terms of joint contributions of the actual wurtzite structure in the one hand and of residual stress fields in the other hand This enables us to give a relationship between the optical transition energies and the in-plane biaxial stress in the layers.

Raman spectroscopy is used to investigate strong band bending at the interface in semi-insulating substrates of ZnSe/GaAs heterostructures grown at high epitaxy rates. Direct evidence is given of the enhancement of polar modes strength, on the substrate side, by the electric field of the space-charge zone associated with Fermi-level pinning. The latter is qualitatively analyzed by following band flattening under illumination through the evolution of interfacial coupled LO-phonon-plasmon modes. Corresponding Raman line shapes are discussed within the phenomenological approach of D. H. Hon and W. L. Faust [Appl. Phys. 1, 241 1 (1973)].

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.

The optical properties of GaN epilayers grown by metal-organic vapor-phase epitaxy on (0001)-oriented sapphire are investigated by means of photoluminescence, reflectance, and differential spectroscopy. We obtain quantitative information about the intrinsic or extrinsic nature of the 2 and 300 K photoluminescence features. From detailed investigations of the reflectance properties of these layers we can quantify the residual strain field in these layers and determine the GaN deformation potentials. Comparison of these values with quantities measured on other semiconductors with wurtzite symmetry is also addressed. Last we utilize photoreflectance spectroscopy to measure exciton binding energies.

We have studied the stimulated emission of MOVPE-grown quantum wells of Zn0.78Cd0.22Se, sandwiched between two thicker, zinc-richer layers. The gain of these samples has been measured, as a function of temperature, using the variable strip-length method. Its mechanism has been shown to be the radiative recombination of an inhomogeneously broadened exciton system.

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.

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.