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Crystallographically aligned GaN nanobelt arrays were synthesized through a hybrid process of Au-assisted nucleation followed by non-Au-assisted anisotropy vapor–solid growth on a (100) γ-LiAlO2 substrate. To the best of our knowledge, this is the first report on aligned GaN nanobelts. [ABSTRACT FROM AUTHOR]

Synthesis of GaN nanoparticles (NPs) by a novel chemical co-precipitation method and the effect of nitridation temperature on the structural, optical and electrical properties have been reported. X-ray diffraction and high resolution transmission electron microscopy show the hexagonal wurtzite structure and highly crystalline nature of the GaN NPs. A strong blue luminescence was observed for all the GaN NPs at room temperature photoluminescence studies. Nevertheless, red and yellow luminescence were absent at the nitridation temperature of 1000 °C. The phonon frequency mode at the k-point of the Brillouin zone symmetry was observed at 271-273 cm-1 for GaN NPs by micro-Raman spectroscopy, which is normally absent for bulk GaN. The carrier concentration and mobility of GaN NPs synthesized at higher temperature were calculated to be 1.36 x 1017 cm-3 and 433 cm² V-1 s-1, respectively, by the Raman line shape analysis of the longitudinal-optical-phonon-plasmon coupled mode. [ABSTRACT FROM AUTHOR]

Helical gallium nitride nanowires were synthesized by chemical vapor deposition using a Pt catalyst. The prepared helical GaN nanowires with a single-crystalline hexagonal wurtzite structure have a coil diameter of 150-280 nm and lengths of up to tens of micrometers. The helical GaN nanowires have six equivalent 〈0 $$ \bar{1} $$ 11〉 growth directions along the [0001] axis. Field emission measurements show that helical GaN nanowire sheets possess excellent field emission properties, with a low turn-on field of ~4.5 V/ μm and a high field enhancement factor of ~2,751. It is believed that this material's excellent electron emission behavior can be attributed to its unique three-dimensional spiral structure. The growth mechanism of helical GaN nanowires has also been analyzed. [ABSTRACT FROM AUTHOR]

We examine the potentialities of heterosegregation processes in the synthesis of surface phases, as exemplified by the preparation of oriented GaN on single-crystal GaAs. A new phase has been obtained for the first time by reacting liquid gallium resulting from surface autosegregation on gallium arsenide with nitrogen gas at temperatures from 970 to 1050°C. The nanomorphology, elemental composition, and phase composition of the surface GaN layer produced by surface reactions have been assessed by high-resolution scanning electron microscopy, digital optical microscopy, and X-ray microanalysis. [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]

Although the (GaN)1-x(ZnO)x solid solution is one of the most effective systems for driving overall solar water splitting with visible light, its quantum yield for overall water splitting using visible light photons has not yet reached ten percent. Understanding and controlling the nanoscale morphology of this system may allow its overall conversion efficiency to be raised to technologically relevant levels. We describe the use a Ga2O3(ZnO)16 precursor phase in the synthesis of this phase which naturally results in the production of arrays of nanorods with favorable diameters (~100 nm) and band gaps (~2.5 eV). Substantial absorption within the band gap is observed, part of which is found to follow the E-3 scaling characteristic of free carriers scattered by ionized impurity sites. Compositional analysis suggests that a substantial quantity of cation vacancies (~3%) may be present in some samples. The typical nanorod growth direction and dominant {1011} facet for powders in this system have been identified through electron microscopy methods, leading to the conclusion that polarity may play an important role in the high photoactivity of this family of wurtzite semiconductors. [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]

Gallium nitride materials are at the forefront of nanoelectronic research due to their importance for UV optoelectronics. In this contribution, we present a facile and well-controlled synthesis of GaN nanodisks by rapid thermal ammonolysis of complex gallium fluoride precursor. We observed the formation of GaN nanodisks in 150 s at 800 °C. The structural properties of GaN were investigated by X-ray diffraction, Raman spectroscopy, and micro-photoluminescence. The morphology of GaN was investigated by scanning electron microscopy and the magnetic properties by superconducting quantum interference device (SQUID) techniques. The morphology of nanodisks was strongly influenced by the temperature of synthesis. The structure characterization shows a high concentration of defects related mainly to the vacancies of N and Ga. The magnetic measurement by SQUID shows paramagnetic behavior induced by structure defects. These findings have a strong implication on the construction of modern optoelectronic nanodevices. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the direct measurement of the strain state at the surface of nanostructures by in-plane X-ray diffraction. GaN tapered nanopillars have been fabricated by dry etching of a highly strained epilayer. The strain of the surface as function of pillar height shows an exponential relaxation which can be described by a single relaxation parameter. Additionally, we have simulated the strain relaxation and distribution of nanopillars. The impact of the pillar geometry on the strain relaxation has been discussed. In agreement with the measurements, an exponential relaxation of the strain is observed. [ABSTRACT FROM AUTHOR]

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]

The possibility that GaN charged nanoparticles might be generated during the synthesis of GaN nanostructures was examined in an atmospheric-pressure chemical vapor deposition (CVD) process using a differential mobility analyzer combined with a Faraday cup electrometer. Both positively and negatively charged nanoparticles in the size range of 10–100 nm were generated in the reactor of the CVD process using Ga2O3 precursor and NH3 gas. With decreasing flow rate of NH3 from 400 to 0 standard cubic centimeter per min (sccm) and decreasing reactor temperature from 1100°C to 500°C, the size and the number concentration of charged nanoparticles decreased. As the size and the number density decreased, the size of deposited GaN hexagonal crystals decreased and eventually GaN nanowires began to grow without catalysts. Copyright 2012 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

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]

In this paper, we presented AlGaN/GaN MIS-HEMT with a 6-nm ALD La2O3 as gate insulator. The gate leakage current had been greatly reduced at both positive and negative bias by using La2O3 gate dielectric. Threshold voltage for MIS-HEMT moved +1 V toward positive direction compared with the Schottky gate HEMT (HEMT) demonstrating the negatively fixed charges at La2O3/AlGaN interface. Besides, the transconductance of MIS-HEMT was not degraded. The stability of fixed and trap state introduced by La2O3 gate dielectric was discussed. [ABSTRACT FROM AUTHOR]

Low thermal resistance GaN-on-diamond wafers offer enhanced thermal management with respect to GaN-on-SiC devices. The GaN/diamond interfacial thermal resistance can contribute significantly to the total device thermal resistance and must therefore be minimized to gain the maximum benefit from GaN-on-diamond. A contactless thermoreflectance measurement technique has been developed, which can be used after wafer growth and before device fabrication, enabling rapid feedback about the influence of growth parameters on interfacial thermal resistance. A measured \(2\times \) reduction in the GaN/diamond interfacial resistance is achieved by reducing the dielectric thickness between the GaN and diamond from 90 to 50 nm, enabling a potential 25% increase in transistor power dissipation for GaN-on-diamond. [ABSTRACT FROM AUTHOR]

A GaN MIS-HEMT with nitrogen (N)-passivation for power device applications is demonstrated. In this letter, nitrogen radicals were adopted to recover nitrogen-vacancy-related defects which were formed due to the thermal decomposition and evaporation of nitrogen atoms from GaN surface during high-temperature process. Besides, nitrogen radicals can also remove impurities and reduce surface dangling bonds by forming Ga-N bonds on the SiN/GaN interface. With N-passivation, the device shows high ON/OFF current ratio, steep subthreshold slope, low OFF-state leakage current, high breakdown voltage, and improved dynamic ON-resistance. The device reliability under high-electric field stress was also improved as a result. [ABSTRACT FROM AUTHOR]

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]

InGaN alloys have been attracting tremendous interest because of the large range of wavelengths covered when tuning the In to Ga ratio, offering extensive band gap engineering possibilities as well as the opportunity to achieve longer wavelength optoelectronic devices. Industrialization of InGaN materials with large In contents is however still limited by challenges imposed by intrinsic material properties. At typical InGaN growth temperatures the In desorption rate is lower than the In–N bond decomposition rate, making it difficult to avoid accumulation of metal In droplets on the surface. Hestroffer et al. (pp. 626–629) have established a growth diagram for InGaN grown on (0001) GaN at a constant temperature of 575 °C versus Ga and In fluxes. The authors identify different regimes, namely: N‐rich, intermediate In‐rich, droplet‐accumulation In‐rich, and Ga‐rich. Compositionally graded InGaN layers are grown by ramping the In and Ga fluxes in parallel under two distinct growth regimes. Structural and optical properties of the two types of grades are compared. The growth diagram proves to be a useful tool in controlling the metal fluxes and thereby the stoichiometry conditions on the surface during the growth of compositionally graded layers. [ABSTRACT FROM AUTHOR]

We report nano-selective area growth (NSAG) of BGaN by MOCVD on AlN/Si(111) and GaN templates resulting in 150 nm single crystalline nanopyramids. This is in contrast to unmasked or micro-selective area growth, which results in a multi-crystalline structure on both substrates. Various characterization techniques were used to evaluate NSAG as a viable technique to improve BGaN material quality on AlN/Si(111) using results of GaN NSAG and unmasked BGaN growth for comparison. Evaluation of BGaN nanopyramid quality, shape and size uniformity revealed that the growth mechanism is the same on both the templates. Further STEM analysis of BGaN nanopyramids on AlN/Si (111) templates confirmed that these are single-crystalline structures without any dislocations, likely due to single nucleation occurring in the 80 nm mask opening. CL results correspond to boron content between 1.7% and 2.0% in the nanopyramids. We conclude that NSAG is promising for growth of high-quality BGaN nanostructures and complex nano-heterostructures, especially for low-cost silicon substrates. [ABSTRACT FROM AUTHOR]

Planar (In,Ga)N layers were grown on nanostripe arrays composed of InGaN/GaN multi quantum wells (MQWs) by metal–organic chemical vapor deposition. The MQW nanostripe arrays with height to width aspect ratios of about 0.5 and 1 were fabricated from planar coherently strained InGaN/GaN MQW samples. Independent of their aspect ratio, the nanostripes exhibited elastic relaxation perpendicular to the stripe direction after pattern fabrication, resulting in an a⊥ lattice constant perpendicular to the stripe direction larger than that of the GaN base layer. In a subsequent step, (In,Ga)N layers were grown on top of the nanostripe arrays, leading to the formation of planar films with a similar a⊥ lattice constant as the MQW stripes beneath. Bright luminescence was recorded from the planar, partially relaxed re-grown (In,Ga)N layers grown on the stripe arrays with an aspect ratio of 1. Plastic relaxation of the MQW stripes was observed after (In,Ga)N regrowth for samples with a stripe aspect ratio of 0.5, leading to luminescence quenching. [ABSTRACT FROM AUTHOR]

In this paper, we performed a high-resolution measurement of channel temperature rise in GaN-based high electron mobility transistors (HEMTs). Cathodoluminescence spectroscopy in the scanning electron microscope was used to probe the temperature rise with several tens of nanometers spatial resolution and accuracy better than ±8 °C. We also determined the temperature distribution and peak temperature change with the power density in active AlGaN/GaN HEMTs in the source–gate and gate–drain openings. The measured results agree reasonably well with physical 2D electrothermal simulations and Raman thermography. [ABSTRACT FROM AUTHOR]

GaN-on-Si transistors attract increasing interest for power applications. However, the breakdown behavior of such devices remains below theoretical expectations, for which the Si substrate is typically made responsible. In this work, the effect of the thickness of an aluminum nitride buffer layer on the vertical breakdown voltage, measured relative to a grounded silicon substrate, has been investigated. A voltage-polarity-dependent breakdown mechanism has been observed. It has been found that the breakdown in the positive bias voltage regime is initiated by carrier injection, for which the carriers originate from an inversion channel formed between the epitaxial layers and the p-silicon substrate. TCAD simulations have confirmed the proposed explanations, and suggest that appropriate modification of the electronic structure at the AlN/silicon interface could significantly improve the vertical breakdown voltage. [ABSTRACT FROM AUTHOR]