We have investigated the heteroepitaxy of indium nitride (InN) directly grown on nitridated sapphire substrates having different orientations. Growths were performed on C, A, M and R-plane oriented sapphire in order to analyse the substrate orientation effect on the structural, optical and electronic properties of as-grown InN. Atomic force microscopy imaging on the InN epilayers revealed different surface morphologies with crystallites well organized along a crystalline orientation of the layer. We have studied the structural anisotropy observed in these layers analysing high-resolution X-ray diffraction rocking curve experiments as a function of the in-plane beam orientation. A-plane oriented InN grown on R-plane sapphire substrate shows a polarized photoluminescence anisotropy, with an anisotropy percentage of about 33%. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this work we present a comprehensive study on the hydrogen impurities, free electron, and structural properties of MOVPE InN films with state-of-the-art quality. We find a correlation between the decrease of free electron concentration and the reduction of bulk hydrogen in the films upon thermal annealing, while no changes in the dislocation densities and strain are observed. Our results suggest that hydrogen is a major source for the unintentional n-type doping in MOVPE InN. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The development of high brightness LEDs is being studied worldwide due to the expectation to replace present light sources because of the higher efficiency and estimated lifetime. The deposition of the epitaxial layers is the most critical step of the LED manufacturing process and has to be carried-out in well controlled conditions to get the necessary uniformity of the epitaxial layers and the proper cleanliness. The most common technology to grow the epitaxial layers is MOVPE, a technology that requires a large quantity of gas to transport the precursors into the process reactor. Control of the cleanliness of the gases used during the process (hydrogen, ammonia, arsine, etc) is necessary to obtain highly efficient and reproducible devices. However, even the use of the cleanest gas source cannot avoid the introduction of impurities when the gas is used in the process reactor. In fact there are several causes that can degrade the actual purity level: the degree of emptiness of the source cylinder, improper procedures during the change out of the cylinder or outgassing from the components in the gas distribution system. These effects can be even worse in research centers where the gas consumption is low and not continuous. A common way to get rid of the above mentioned problems is the adoption of point of use purifiers. Results showing the improvements in the gas quality by adopting point of use purifiers will be presented and discussed. The differences between some widely used hydrogen purification technologies in the compound semiconductor applications will also be evaluated. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The natural aging process occured in indium nitride quantum dots (QDs) heterostructures as a consequence of exposure to the atmosphere has been studied by means of transmission electron microscopy and electron beam related techniques. The comparison between GaN-capped and uncapped InN QDs kept at room conditions during 36 months indicates the structural changes that take place. While the capping layer seems to act in a protective way avoiding any change in the QDs, the uncapped structures suffer a series of phase transformations, where the original wurtzite structure is replaced by a layer of cubic phases. The main constituent of this layer is shown to be bcc-In2O3 formed by the substitution of the nitrogen atoms by oxygen from the atmosphere. This supposes a transformation from a hexagonal to a cubic structure, explained by the existence of an oxygen-rich cubic InN acting as an intermediate phase. The difference in the formation enthalpy between the original and the final product, together with the good match between the crystals would explain this transformation that shows the high instability of InN at environmental conditions.

We have investigated the heteroepitaxial growth of indium nitride on sapphire substrates having different orientations. Growths were performed on C-, A-, M-, and R-plane-oriented sapphire in order to analyze the substrate orientation effect on the structural, optical, and electronic properties of InN. The orientation relationship between InN and sapphire was deduced by theta/2 theta High-resolution X-ray diffraction (HRXRD) measurements. These experiments show the ability to grow InN along nonpolar (11 (2) under bar0) orientation and the semipolar (11 (2) under bar2) orientation, depending of the orientations of the sapphire substrate. The crystalline quality was assessed by XRD symmetric and asymmetric rocking curve. measurements. We observed no drastic disparity between our samples, all exhibiting a reasonable crystalline quality. Atomic force microscopy imaging on these, layers, revealed different surface morphologies with a roughness varying between 30 and 60 nm. Electrical properties of the InN samples were investigated by room temperature Hall effbt.Cmeasourements and a line shape fitting of the photoluminescence was performed in order to get optically the values of the residual carrier density in the nitride layers. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Since a few years, indium nitride promising properties for device applications have attracted much attention worldwide. Huge efforts are dedicated to optimize indium nitride growth. However, this growth is extremely challenging, in particular using the metal organic vapor phase epitaxy (MOVPE) technique which exhibits very low growth rates. This may explain why most of the samples available in the scientific community, which also present the best electrical properties, were grown by molecular beam epitaxy (MBE). However, up to date, no intrinsic indium nitride layer was obtained. InN epilayer crystalline quality suffers from the lack of lattice matched substrates, leading to the use of double-step growth process. In this paper, we show that InN low lateral growth rate is a limiting parameter for efficient double-step growth process. But, we also report that the use of CBrCl3 during InN growth enhances the lateral growth rate. To improve the growth rate along the c-axis, we investigate alternative precursors for both nitrogen and indium species. We show that ammonia remains the best precursor, but combined with triethylindium, the growth rate increases with optimum crystalline quality. Finally, we compare MOVPE-grown and MBE-grown InN layers in order to understand the difference observed on the electrical properties. We show how thermal annealing can improve the MOVPE-grown InN layers leading to similar electrical properties than reported in MBE-grown samples. The role of ammonia as source of hydrogen is also discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim