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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]

A novel serpentine-channeled mask was introduced to Si substrate for low-dislocation GaN epitaxial growth and the fully coalesced GaN film on the masked Si substrate was achieved for the first time. Compared with the epitaxial lateral overgrowth (ELOG) growth method, this innovative mask only requires one-step epitaxial growth of GaN which has only one high-dislocation region per mask opening. This new growth method can effectively reduce dislocation density, thus improving the quality of GaN significantly. High-quality GaN with low dislocation density ∼2.4 × 10 7  cm −2 was obtained, which accounted for about eighty percent of the GaN film in area. This innovative technique is promising for the growth of high-quality GaN templates and the subsequent fabrication of high-performance GaN-based devices like transistors, laser diodes (LDs), and light-emitting diodes (LEDs) on Si substrate. [ABSTRACT FROM AUTHOR]

Ga(S2CN(CH3)2)3(Ga(mDTC)3) nanoparticles (NPs) were prepared using ultrasonic spray method, and well mono-dispersed, with a mean particles size of 82 nm. Ga(mDTC)3NPs changed into Ga2S3at 300°C under N2environment, and the spin-coated films transformed into GaN films above 700°C under NH3environment. From these results, Ga(mDTC)3films were transformed into γ-Ga2S3films by thermal decomposition, and S elements were substituted simultaneously by N elements. In this stage, the pyrolytic GaN film underwent a recrystallization process, and a preferred direction of GaN films was mainly aligned to z-axis direction due to the lower energy surface of hexagonal structure. [ABSTRACT FROM AUTHOR]

Growth conditions have a tremendous impact on the unintentional background impurity concentration in gallium nitride (GaN) synthesized by molecular beam epitaxy and its resulting chemical and physical properties. In particular for oxygen identified as the dominant background impurity we demonstrate that under optimized growth stoichiometry the growth temperature is the key parameter to control its incorporation and that an increase by 55 °C leads to an oxygen reduction by one order of magnitude. Quantitatively this reduction and the resulting optical and electrical properties are analyzed by secondary ion mass spectroscopy, photoluminescence, capacitance versus voltage measurements, low temperature magneto-transport and parasitic current paths in lateral transistor test structures based on two-dimensional electron gases. At a growth temperature of 665 °C the residual charge carrier concentration is decreased to below 1015 cm−3, resulting in insulating behavior and thus making the material suitable for beyond state-of-the-art device applications. [ABSTRACT FROM PUBLISHER]

Abstractauthoren We propose partially relaxed ultrathin GaN interlayer for strain control of AlN on SiC substrates. According to the degree of relaxation of the GaN interlayer, the lattice constant of the interlayer changes from that of SiC to that of bulk GaN, which leads to strain control of an AlN top layer grown on the interlayer. Growth of these layers is conducted by plasma-assisted molecular beam epitaxy. Before growing the interlayer, an AlN layer coherently grown on SiC is used as a template layer. The interlayers that have different degrees of relaxation are successfully obtained by changing the interlayer thickness. As a result, strain values of the AlN top layer grown on the interlayers are widely controlled from compressive (−0.53%) to tensile (+ 0.07%). TEM observation revealed the relaxation is induced by U-shaped half-loop dislocations originating from the GaN interlayer. [ABSTRACT FROM AUTHOR]

We present a detailed atomistic analysis of the electronic properties of m-plane InGaN/GaN quantum wells. The tight-binding model used treats realistically sized systems atomistically and accounts for compositional and structural inhomogeneities. Local variation in strain and built-in potential arising from random alloy fluctuations are explicitly included in the model. Many energy states of the supercells considered are calculated in order to determine the impact of the alloy fluctuations on the electronic structure of the system under investigation. We find that while the electrons are relatively insensitive to the local indium environment, the hole states are highly sensitive to it and are subject to very strong localization effects. These effects persist several states into the valence band. This strong localization of the hole states leads to a very broad distribution of ground state energies in different random configurations. Furthermore, we see that the localization leads to poor overlap between different hole states resulting in a reduced probability of transfer of carriers between different states. This feature should play an important role for transport properties in m-plane InGaN/GaN QWs. [ABSTRACT FROM AUTHOR]

GaN layers have been grown on double-side-polished sapphire substrates using hydride vapor phase epitaxy. The GaN layers on each side of the substrate were alternately grown using a new susceptor with a rotating mechanism. Although a conventional GaN layer grown on one side of a sapphire substrate exhibits a small radius of curvature, the alternately double-sided-grown GaN template exhibits a large radius of curvature. The radius of curvature of the alternately double-sided-grown GaN template with a thickness of 180 μm was found to be approximately 16.4 m, and was larger than the 0.5 m radius of curvature of the conventional GaN template. [ABSTRACT FROM AUTHOR]

Hydride vapor phase epitaxy (HVPE) is used for the growth of low-defect GaN. We have grown undoped films on sapphire and investigated them using steady-state and time-resolved photoluminescence (PL). One of the dominant PL bands in high-quality GaN grown by HVPE is the green luminescence (GL) band with a maximum at 2.4 eV. This PL band can be easily recognized in time-resolved PL measurements due to its exponential decay even at low temperatures (<50 K), with a characteristic lifetime of 1-2 μs. As the temperature increases from 70 K to 280 K, the PL lifetime for the GL band increases by an order of magnitude. This unusual phenomenon can be explained on the assumption that the electron-capture coefficient for the GL-related defect decreases with temperature as T. [ABSTRACT FROM AUTHOR]

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]

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]

A new approach is proposed to the synthesis of a semipolar GaN on a Si(100) substrate at the surface of which the V‐shaped nanostructures with the characteristic size of elements as low as 100 nm are formed. It has been demonstrated that application of buffer layers of 3C‐SiC and AlN enables formation of the GaN(10–11) layer characterized by the full width at half maximum value as low as ωθ ≈45 arcmin for the X‐ray diffraction rocking curve. The model based on anisotropic nucleation of AlN on the V‐shaped nanostructure is proposed to explain the growth of the GaN layer in a single semipolar direction. In this article, Bessolov et al. focus on the growth of the GaN layer in a semipolar direction by heteroepitaxy of the GaN layer on nano‐patterned Si(100) substrate with V‐shaped nano‐grooves arranged with the period as low as 100 nm, combined with the synthesis of a nano‐sized SiC layer formed by solid‐phase substitution of silicon atoms by carbon atoms. [ABSTRACT FROM AUTHOR]