We have studied plasmon-longitudinal optical (LO) phonon coupled modes by means of Raman scattering in n-type InN layers grown by metalorganic vapor phase epitaxy, for carrier densities in the range of 10(19) cm(-3). A strong mode is observed near the frequency of the A(1)(LO) phonon, despite the high conductivity of the films. It is suggested that the main origin which can be invoked for an effective decoupling of the LO phonon from the plasmon is the participation to the scattering of phonons with wave vectors larger than the Thomas-Fermi wave vector. The line shape of the LO mode is calculated using the Lindhard-Mermin dielectric function taking into account finite wave-vectors, for various light scattering processes. We find that the charge density fluctuations mechanism is involved as the main scattering mechanism in n-type InN, at least for the investigated excitation energies in the 2.54-1.89 eV range. The breakdown of the wave-vector conservation is assigned to electron elastic scattering by impurities.

The 800 meV photoluminescence band in indium nitride is excited under pulsed excitation conditions and is investigated as a function of temperature and time. Our results are consistent with a composite photoluminescence feature composed of two overlapping bands separated by an similar to 10 meV splitting, with populations described by a thermal equilibrium model. Efficient nonradiative recombination channels rule both the temperature dependence of the time-integrated photoluminescence spectra and the recombination dynamics. At 10 K, the radiative recombination time is of the order of 300 ns, while the nonradiative recombination time, which is ruled by activation energy of 8 meV, is about 100 ps. (C) 2005 American Institute of Physics.

We report on the optical characterization of InN layers in the THz range and magnetic fields up to 13 T. The results are interpreted using the dielectric function formalism, with contributions of cyclotron resonance, phonons, plasmons and helicon wave excitations. We show how THz radiation transmission measurements can provide an optical contactless method of determining the quality (carrier density and momentum scattering rate) in the InN layers. (c) 2005 WILEY-VCH Verlag GmbH W Co.

We report a detailed study of the optical properties unintentionally doped and n-doped InN films grown by Metal Organic Vapour Phase Epitaxy. When increasing the doping, a blue-shift of the absorption and reflectance spectra is found that we quantitatively correlate with the doping. Our measurements give us the value of the two-band Kane model parameter: 12 eV and an asymptotic value for the InN band gap at 300 K: 1160 meV. Moss-Burstein shift and band gap renormalization effects are computed as well as a non-parabolic effective mass. This is found to equal 0.09 m, in the unintentionally doped case. The photoluminescence spectra are strongly redshifted with respect to the bandgap and are always peaking near 760 meV. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on comparative studies of basic properties of indium nitride quantum dots (QDs) grown by metal organic vapour phase epitaxy (MOVPE) on GaN, AlN and Si(111). Variation of the growth parameters, such as the growth temperature, deposition time, and the V/III ratio, allowed us to control characteristic sizes and a density of the QDs. With similar growth parameters, both mean height and aspect ratio of the dots are increased in a GaN, AlN, Si line. The InN QDs have been encapsulated by different materials that permit us to investigate their optical response with optical excitation, whose origin, either luminescent or scattered, is discussed. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

InN is a very promising material for optoelectronics, high frequency devices and terahertz applications. However, there is no convenient matched substrate and, InN is usually grown onto sapphire. Due to the large attice mismatch and the dissimilarity in atomic arrangement, the epitaxial growth of InN onto sapphire Is a challenge. The initial stages of the growth are of primary importance for the obtention of high quality InN films. Epitaxial InN layers can be improved by nitriding the substrate but the quality of InN strongly depends on the temperature and time of nitridation used. We investigated the effect of these parameters on the crystalline quality, morphology, optical and electrical properties of InN layers. Raising the temperature and the time of nitridation is not beneficial. We also studied the effect of different buffer layers (CaN, AlN). Growth on template seems to be better than on low-temperature buffer (GaN and AlN). After optimising all parameters, we obtained InN layers on lightly nitrided sapphire which correspond, up to know and in our knowledge, to the best results in MOCVD low pressure: the layer growth mode is 2D, with a root mean square roughness of 0.62nm, a reproducible mobility of 800cm(2)/Vs and an electron concentration about 9x10(18) cm(-3). (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.