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Abstract Rutherford Backscattering Spectrometry in random (RBS) and aligned (RBS/C) to GaAs 001 -channel, and Transmission Electron Microscopy (TEM) techniques were employed to characterize the GaN nanolayer obtained by Ion Beam Synthesis (IBS). N+ ions at 50 keV were implanted up to a fluence of 3 × 1017 cm−2 into a 001 GaAs substrate capped by 125 nm Si 3 N 4 layer obtained by sputtering deposition. N+ implantation was performed with samples held at 450 °C, which were subsequently annealed in a temperature range between 550 and 1000 °C for 5 min by Rapid Thermal Annealing (RTA) under N 2 flow. TEM demonstrated a layered structure on the as-implanted sample, with N bubbles formed at around Si 3 N 4 /GaAs interface. RBS/C analysis carried out on samples annealed at distinct temperatures revealed a threshold temperature of about 850 °C to fully convert the as-implanted layered structure into a GaN nanolayer. At this temperature and above, the GaAs implanted side of the former Si 3 N 4 /GaAs interface was converted into GaN. As a result, an underneath voids structure was also formed indicating an intense migration of Ga from deeper areas of the GaAs substrate. RBS showed results compatible with a GaN nanolayer rich in N for the 850 °C annealing, whose sample also offered canalization (χ min = 63%) along the GaAs 001 -channel. However, a regression in the crystalline quality (χ min = 95%) was observed for the 1000 °C anneal. [ABSTRACT FROM AUTHOR]

Highlights • Gallium Nitride (GaN) based-hydrogen gas sensor for high temperature application were prepared. • GaN powder with different oxygen impurities were synthesized from α-GaOOH by a direct nitridation method. • Oxygen presence is behind the enhanced gas sensing sensitivity of GaN. • Band energy structure and carrier concentration of GaN are affected by oxygen content. • The obtained GaN-sensor exhibited excellent sensitivity than its oxide (β-Ga 2 O 3). Abstract Extremely stable gas sensors at elevated temperature (T > 400 °C) with rapid detection of hydrogen gas are urgently demanded especially for hydrogen production industry which typically involves a high-temperature system. Gallium nitride (GaN) possesses excellent physicochemical properties and is expected to be one candidate for high temperature gas sensor. In this work, the GaN preparation from α–GaOOH precursors by a direct nitridation method under NH 3 flow is presented. The nitridation was done at various temperatures to obtain GaN with different oxygen contents, which played a vital role in gas sensing response of thick film GaN in various concentration of H 2 gas at 500 °C. The sensitivity of the obtained GaN with 2.07 wt.% of oxygen content was 10 times higher than that sample with the lowest oxygen content (1.9 wt.%) and the sensitivity drastically decreased when the oxygen content was 2.53 wt.%. The sensors also demonstrated high stability as indicated by their repeatable feature after being exposed at a various concentration of H 2 (150–750 ppm). Furthermore, the GaN showed higher sensitivity than that of β–Ga 2 O 3 sensor. [ABSTRACT FROM AUTHOR]

Colloidal GaN nanoparticles were synthesized in distilled water by pulsed laser ablation (PLA) method. Optical and structural analysis were performed on samples generated under different laser fluence by using ultraviolet–visible (UV–vis) absorption spectrophotometer, X-ray diffractometer (XRD) and Tunneling Electron Microscope (TEM) technique. The mean size and size distribution of the nanoparticles were investigated using image processing technique of collected TEM images, in addition to XRD patterns. It is shown that laser fluence has a significant effect on nanoparticles size properties. Also, it is proven that the ablation process affects the nanoparticles size and size distribution. The results show that higher laser fluence produces larger mean size of nanoparticles with a broader size distribution. [ABSTRACT FROM AUTHOR]

GaN nanowires were synthesized on sapphire substrates by chemical vapor deposition. The selective growth of GaN nanowires was obtained through an N-Ga2O3 layer prepared by radio frequency magnetron sputtering. The X-ray diffraction (XRD) and Raman measurements indicated the GaN nanowires to be all indexed to the hexagonal wurtzite structure. The photoluminescence (PL) spectra were composed of a strong UV emission peak (365nm) and a weak yellow luminescence (YL) band (~600nm). The selective growth mechanism of GaN nanowires was briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this research, hexagonal wurtzite structure gallium nitride (GaN) thin film was grown on silicon (Si) substrate by using spin coating deposition method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. High resolution X-ray diffraction results revealed that wurtzite structure GaN thin film with (002) preferred orientation was deposited on Si substrate. Flied-emission scanning electron microscopy and atomic force microscopy results showed that crack free GaN thin film with uniform and dense grains of GaN was formed. Finally, lattice vibrational characterization by p-polarized infrared reflectance technique revealed a strong reststrahlen feature of crystalline wurtzite GaN, and the transverse and longitudinal phonon modes of wurtzite GaN were clearly identified. [Copyright &y& Elsevier]

Abstract: Sb/P co-doped Gallium Nitride (GaN) nanowires were synthesized via a simple chemical vapor deposition (CVD) process by heating Ga2O3 and Sb powders in NH3 atmosphere. Scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS) measurements confirmed the as-synthesized products were Sb/P co-doped GaN nanowires with rough morphology and hexagonal wurtzite structure. Room temperature cathodoluminescence (CL) demonstrated that an obvious band shift of GaN nanowires can be observed due to Sb/P co-doping. Possible explanation for the growth and luminescence mechanism of Sb/P co-doped GaN nanowires was discussed. [Copyright &y& Elsevier]

Highlights: [•] GaN NWs were synthesized through a simple and friendly strategy. [•] The work function of GaN NWs was measured by low energy XPS. [•] The influence of components of GaN NWs with the work function was analyzed. [•] The relationship of the structures of GaN NWs and the FE property was discussed. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of novel GaN nanotowers on silicon (111) substrates by employing ultrathin Ni catalyst films (0.2nm) were successfully synthesized at different growth temperatures using a metal–organic chemical vapor deposition system. Scanning electron microscopy indicated that the density and growth direction of the nanotowers were highly sensitive to changes of growth temperature. The morphologies were characterized in detail, and showed triangular and hexagonal nanotowers which were oriented predominantly along and [0001] directions, respectively. Finally, a new growth mechanism is stated to explain the growth of these two novel GaN nanotowers. [Copyright &y& Elsevier]

Abstract: GaN synthesized by close space vapor transport in vacuum using GaN powder as the source material is reported. According to X-ray diffraction measurements, samples grown onto sapphire substrates are polycrystalline with the wurzite structure, while those grown onto fused silica substrates are amorphous. Scanning electron microscope and energy dispersive spectroscopy results show that the surface of the samples is composed of rounded droplets of GaN. Room temperature photoluminescence shows near band-edge emission and a broad defect band. Possible mechanisms allowing the deposition of GaN from the vapors of GaN powder are discussed. [Copyright &y& Elsevier]

Abstract: The properties of GaN semiconductors are strongly dependent on the shapes, sizes, and dimensionalities. So it would be interesting to synthesize GaN with various morphologies for different applications. In this article, Ga2O3 cauliflowers were obtained by a solvothermal process at 180°C for 36h, which was further converted into wurtzite GaN cauliflowers by calcinations in the flow of NH3 gas at 800°C for 100min. The synthesized Ga2O3 and GaN microspheres were characterized using FESEM, TEM, TGA, Raman and PL. The FESEM and TEM observations suggest that the GaN product retained essentially the same basic topological morphology in contrast to that of the Ga2O3 precursor. The initial Ga2O3 structural motifs were unaffected by the subsequent high temperature chemical transformations process. The TGA tests indicate that the as-prepared GaN has excellent thermal stability and anti-oxidation property that will make it particularly useful for high temperature applications. The Raman and PL results indicate that GaN cauliflowers prepared in our experiment have excellent optical properties. [Copyright &y& Elsevier]

Abstract: It would be interesting to synthesize GaN with various morphologies for different applications. Herein, the synthesis of GaN microrods is demonstrated. The synthesis involved two steps: first, hydrothermal synthesis of GaOOH microrods at 190°C for 24h; second, preparation of GaN microrods in the flow of NH3 gas at 850°C for 90min. The synthesized GaOOH and GaN microrods were characterized by FESEM, suggesting that the initial GaOOH structural motifs were unaffected by the high temperature chemical transformations process. It was found that a slower heating rate (1°Cmin−1) is beneficial to keeping the 1D skeleton of and GaN, while GaN nanoparticles with minor microtubes were obtained with a higher heating rate (10°Cmin−1). Raman spectroscopy and PL spectrum of the as-prepared GaN product have been performed. The photoluminescence measurement reveals that the as-prepared wurtzite GaN microrods showed strong blue-violet emission. [Copyright &y& Elsevier]

Abstract: GaN was synthesized onto sapphire substrates by chemical vapor deposition, reacting gallium, ammonium chloride and ammonia. The polycrystalline films were immersed in glycine, aspartic acid and cysteine solutions. Cysteine chemisorbed onto GaN films produced detectable changes in conductivity, mobility and Hall coefficient indicating that GaN is capable of detecting and reacting with thiolate groups, which was confirmed by X-ray photoelectron spectroscopy. The Cys-GaN film solution was adjusted to pH 10, upon which the GaN nanoparticles were transferred to the aqueous phase forming a suspension stable for seven days. The alkaline colloid was then further adjusted down to pH 3 retaining stability for three days. The GaN colloid obtained represents a suitable medium to study GaN properties for biological applications. [Copyright &y& Elsevier]

Abstract: The synthesis of GaN by selective area growth using Hydride Vapor Phase Epitaxy (SAG-HVPE) is reported for stripes patterned along and GaN on c-plane sapphire substrates. A systematic control of the GaN morphologies was carried out by both cross-sectional and surface Scanning Electron Microscopy (SEM). A complete HVPE cartography of GaN-SAG revealed domains of zero growth rates at high concentration of hydrogen in the carrier gas. The determination of the mechanisms that govern the growth of GaN morphologies was particularly emphasized. A theoretical model based on thermodynamic and kinetic analyses of the grown (0001) GaN layers was discussed, in combination with experiments on unmasked (0001) GaN and patterned GaN/c-plane sapphire substrates. Long HVPE runs were performed to demonstrate that the prevailing growth mechanism, for high hydrogen concentration in the carrier gas, is a mechanism based on a dechlorination by GaCl2 gas species. This mechanism leads to growth blockade of GaN growth and constitutes a very interesting issue for shaping GaN material as an alternative to top-down micro- and nano-technologies. [Copyright &y& Elsevier]

Abstract: Gallium nitride (GaN) powder was synthesized by the cyanonitridation of β-gallium oxide (β-Ga2O3) powder and characterized by powder X-ray diffraction, 71Ga magic-angle spinning nuclear magnetic resonance spectroscopy, Raman spectroscopy, and scanning electron microscopy. The cyano radical, which was formed by the thermal decomposition of organic compounds such as acetonitrile and melamine, was involved in the nitridation of β-Ga2O3. The formation of GaN via cyanonitridation commenced at slightly higher temperature than that via ammonolysis. The produced GaN powders showed five first-order phonon modes in Raman spectra. Particles’ morphologies were maintained during cyanonitridation, indicating that the β-Ga2O3 did not convert to GaN through gaseous species such as Ga2O. [Copyright &y& Elsevier]