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.

The behavior of the E-2 and A(1)(LO) optical phonons of hexagonal indium nitride under hydrostatic pressure was studied using Raman spectroscopy. Linear pressure coefficients and the corresponding Gruneisen parameters for both modes were determined for the wurtzite structure up to 11.6 GPa, close to the starting pressure of the hexagonal to rocksalt phase transition of InN. Raman spectra acquired within the 11.6 to 13.2 GPa pressure range suggest that wurtzite InN undergoes a gradual phase transition, and the reverse transformation exhibits a strong hysteresis effect during the downstroke.

Europium was implanted into GaN through a 10 nm thick epitaxially grown AlN layer that protects the GaN surface during the implantation and also serves as a capping layer during the subsequent furnace annealing. Employing this AlN layer prevents the formation of an amorphous surface layer during the implantation. Furthermore, no dissociation of the crystal was observed by Rutherford backscattering and channeling measurements for annealing temperatures up to 1300degreesC. Remarkably, the intensity of the Eu related luminescence, as measured by cathodoluminescence at room temperature, increases by one order of magnitude within the studied annealing range between 1100 and 1300degreesC. (C) 2004 American Institute of Physics.

Using measurements of phonons frequencies in large size InN quantum dots deposited by Metal-organic vapor phase epitaxy, we found these frequencies to experience a blue shift with increasing compression. Next we show that all the phonon frequencies reported in the literature are correlated to the strain state of InN and are, within the experimental uncertainty, consistent with each other. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.

With respect to growing indium nitride quantum dots with very low surface densities for quantum cryptography applications, we have studied the metalorganic vapor phase epitaxy of InN onto GaN buffer layers. From lattice mismatch results the formation of self-assembled dots. The effects of the growth temperature, V/III molar ratio, and deposition time are studied, and we demonstrate that quantum-sized dots of InN can be grown with a material crystalline quality similar to the quality of the GaN buffer layer, in densities of 10(7) to 10(8) cm(-2). Such low densities of dots allow for the realization of experiments or devices in which a single dot is isolated, and may be used in the near future to produce single-photon sources. (C) 2003 American Institute of Physics.

We have demonstrated the giant enhancement of second-harmonic generation in a one-dimensional GaN photonic crystal structure caused by the simultaneous achievement of strong fundamental field confinement and quasi-phase matching conditions. We have firstly measured the linear dispersive properties of the resonant modes for various azimuthal directions to predict the quasi-phase matching conditions. The theory based on a rigorous scattering matrix method has provided a good description of the equi-frequency surfaces. We have then shown that the equi-frequency surfaces may be used to identify the angular situations for which the quasi-phase matching conditions can be satisfied. The SHG enhancement achieved due to the double resonance was 5000 times greater than for the unpatterned GaN layer. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.