We have studied the optical properties of Eu doped GaN thin films. We have grown high quality Eu doped GaN thin films by using Gas Source Molecular Beam Epitaxy (GSMBE), with 1.4% Eu concentration. The Full Width at Half Maximum (FWHM) of the X-ray diffraction in an omega scan was found to be 288 arcsecs. Low Eu concentration (0.08%) doped GaN thin films were grown, where Eu-related photoluminescence at 622 and 613 nm was detected using above band-gap excitation at 2 K. For high Eu concentration of 30% GaN:Eu crystal photoluminescence (PL) and cathodoluminescence (CL) spectra show strong and intense transitions at 622 and 664 nm, but also at 593 nm for CL spectra, with a similar transition observed from the low Eu concentration sample. (C) 2004 Published by Elsevier Ltd.

Studies of lattice dynamics devoted to wurtzite InN are presented. Raman scattering experiments on both InN thin films and nanometric islands grown by Metal-Organic Vapor Phase Epitaxy (MOVPE) were performed at room temperature. From the Raman spectra recorded from InN films under hydrostatic pressure up to 13 GPa, linear pressure coefficients and the corresponding Gruneisen parameters for both E-2 and A(1) (LO) phonons were extracted for the wurtzite structure up to 11 GPa, close to the starting pressure of the hexagonal to rock-salt phase transition of InN. Spectra at higher pressure suggest that InN undergoes a gradual phase transition, and the reverse transition exhibits a strong hysteresis effect during the downstroke. Then, we discuss recent results on large single InN islands grown on GaN buffer layers, obtained by spatially resolved micro-Raman measurements. The magnitude of the residual strain is estimated, using a recent determination of phonon deformation potentials. It is found to vary linearly as a function of island height. (C) 2004 Elsevier Ltd. All rights reserved.

We have grown by metal-organic chemical vapour deposition a thick layer of indium nitride (1.4 mum) on a sapphire substrate using appropriate growth parameters. The substrate was then removed and the layer reduced to powder by a soft mechanical method. The resulting material was used to obtain an X-ray powder diffraction profile for completely relaxed indium nitride, i.e. without strain due to the lattice mismatch with sapphire. The diffraction measurement was made with a Phillips XPERT-Pro diffractometer, without slits, and collected using CuKalpha radiation at 300 K.;The powder pattern contains many (hkl) peaks, depending upon two lattice parameters, a and c, for the wurtzite crystal structure. A two-dimensional least squares procedure was adapted to minimize the fitting errors on the experimental data. The lattice parameters were accurately extracted and will be given here. (C) 2004 Elsevier Ltd. All rights reserved.

This study presents the MOVPE growth of InN films onto different substrate materials, including sapphire, nitrided or not, GaN and AlN buffer layers deposited onto sapphire, and Si(111).;For InN growth onto nitrided sapphire, different growth parameters were investigated in order to determine the best growth conditions. We found that a low V/III molar ratio has to be used in order to increase the growth rate. A light nitridation treatment gives the best electrical properties: mirror like layers with a mobility of 800 cm(2)/V s were obtained. At room temperature, reflectivity experiments show the existence of a transition at 1.2 eV, while photoluminescence appears around 0.8 ev.;Using the same growth conditions onto GaN buffers (with thicknesses ranging from 15 to 1000 A), we found that the best mobilities are obtained above a given buffer thickness.;By comparing also with AlN buffer layers and silicon substrates, we found that our previous conclusion still holds; lightly nitrided sapphire substrate leads to the best electrical properties and morphology. (C) 2004 Elsevier Ltd. All rights reserved.

We demonstrate that the phonon frequencies that are reported in the literature for indium nitride (InN), films are all consistently correlated to the strain state of the material. Raman spectroscopy measurements and X-ray investigations of large size InN quantum dots grown on c-plane GaN are combined, which show these frequencies to experience a blue shift with increasing compression. The InN dots are weakly strained, most probably due to the formation of dislocations at the InN/GaN interface. We report the observation of a broad absorption in the 1.25 eV region that is typical of thin InN films. Such a feature we attribute to light absorption at the energy of the fundamental direct band gap of InN, while we attribute the low energy 650-800 meV photoluminescence to an extrinsic recombination process analogous to the processes that produce the blue band in AlN and the yellow band in GaN. (C) 2004 Elsevier B.V. All rights reserved.

We present results for the MOVPE growth of InN films onto sapphire substrates, by direct growth or using a GaN buffer layer. As opposed to common belief, it is shown that a low V/III molar ratio has to be used in order to achieve high quality films. Using the parameters that are presented here, we were able to grow mirror like layers on 2 inch sapphire wafers, with a reproducible mobility of 800cm(2)/VS. This is the best value obtained to date for MOVPE growth. Reflectivity and absorption studies of our layers reveal a marked structure around 1.2 cV, at room temperature. InN quantum dots were also grown on to GaN buffer layers. The dot size and density was controlled by tuning the growth temperature and the molar V/III ratio. The quantum dots that we have grown are flat hexagons, with an aspect ratio of 0.1-0.16, and height down to 2 nm. (C) 2004 Elsevier B.V. All rights reserved.