Nitride semiconductors have been at the center of semiconductor research in the last decade. However Indium nitride is still poorly known, due to its growth difficulty, and its properties are still the subject of passionate debates. Still, it is clear that it is a very promising material for telecommunication optoelectronics and hyperfrequency/terahertz applications. In particular, nanostructures based on InN are extremely interesting, by combining a small bandgap, the incredible efficiency of nitride semiconductors and the tunability of quantum dots. In this paper, we present the latest advances in the growth and optical properties of InN quantum dots grown onto GaN. The optical properties of InN dots will be compared to those of InN films, and we will show that the thermal behaviour of InN dots is far superior. Using TEM and synchrotron radiation diffraction, we will analyze the strain state of the dots at the nanometer scale, along the growth axis of the dots. These results, combined with the thermodynamical analysis of the growth data, will allow us to demonstrate that the growth mechanism is not the usual Stransky-Krastanow mode, but is more related to the BCF (Burton-Cabrera-Franck) model.

The growth of indium nitride quantum dots are studied. An investigation of the dot built-in strain, at the nanometric scale, performed using the synchrotron radiation is presented. These results are correlated with transmission electron microscopy images showing the dot structure. From these results, together with a thermodynamical analysis, it is shown that the dot growth mechanism is not the usual Stranski-Krastanov growth mode, but is more related to the BCF (Burton Cabrera Franck) growth mode.

We analyze the low temperature photoluminescence properties of two multi-layer stacking of GaN/AlN quantum dots. We report drastic differences of linewidths between continuous wave and time-resolved photoluminescence experiments. After the pulsed excitation, time-resolved photoluminescence reveals a substantial red shift of the line, which keeps a fairly constant width. In continuous wave experiments, the screening of internal electric fields by accumulation of e-h pairs in quantum dot planes induces a blue-shift. For samples with large number of quantum dot planes an unexpected narrowing of the emission line is observed when the laser intensity is increased. We assign the observed behaviors of energies and linewidths to the contributions of the in-depth decrease of the degree of excitation of the different planes. Our interpretation is supported by the use of a model based on a self-consistent solution of the Schrodinger and Poisson equations within the envelope function approximation.

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 650-750 meV photoluminescence to an extrinsic recombination process analogous to the process that give the blue band in AlN and the yellow band in GaN. The substantial broadening is attributed to both the residual doping, and strain. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.