Search

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]

Monolithic color synthesis is demonstrated using InGaN/GaN multiple quantum wells (QWs) grown on GaN microstripes formed by selective area epitaxy on SiO2 mask patterns. The striped microfacet structure is composed of (0001) and {11-22} planes, attributed to favorable surface polarity and surface energy. InGaN/GaN QWs on different microfacets contain spatially inhomogeneous compositions owing to the diffusion of adatoms among the facets. This unique property allows the microfacet QWs to emit blue light from the {11-22} plane and yellow light from the top (0001) plane, the mixing of which leads to the perception of white light emission. [ABSTRACT FROM AUTHOR]

High-quality nonpolar m-plane GaN-based light-emitting diode (LED) wafers on LiGaO(100) substrates have been grown in this work by the combination of pulsed laser deposition and molecular beam epitaxy technologies. This work systemically studies the crystalline quality, surface morphology, as well as optoelectronic properties of as-grown nonpolar m-plane GaN-based LED wafers. The as-grown nonpolar m-plane GaN-based LED wafers on LiGaO(100) substrates show good structural properties with estimated dislocation density ∼10 cm and abrupt InGaN/GaN interfaces. A photoluminescence peak at approximately 446 nm with full-width at half-maximum (FWHM) of 21.2 nm is identified at room temperature. A strong electroluminescence (EL) peak observed at 446 nm with FWHM of 20.7 nm is obtained at an injection current of 20 mA. Furthermore, there is a slight blue shift in the EL emission wavelength with increase in the injection current, while the EL FWHM can be kept stable thanks to the absence of the quantum confined Stark effect. This study of high-quality nonpolar m-plane GaN-based LEDs is of paramount importance for future application of high-efficiency GaN-based devices. [ABSTRACT FROM AUTHOR]

Intrinsic and extrinsic gallium nitride (GaN) nanostructures, due to their size tunable photo-physical and photo-chemical behavior, have attracted great interest for the fabrication of various smart optoelectronic devices. In the present paper, GaCoN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles having average size ~4 nm. Spectroscopic studies like energy dispersive X-ray spectroscopy, UV-visible absorption, Fourier transform infra-red spectroscopy, X-ray photoelectron spectroscopy and steady state energy resolved and time resolved photoluminescence spectroscopy studies have been opted for the investigation of quantitative, qualitative and optical behavior of synthesized nanomaterials. [ABSTRACT FROM AUTHOR]

We report improvement of improvement effectiveness of the light extraction efficiency of 10 W operated InGaN-based vertical light-emitting diodes via n-GaN surface roughening, using a commercial photoresist (PR) developer as an etching solution, which was compared with a conventional KOH-based solution. With the conventional KOH-based solution for n-GaN surface roughening, although both the depth and density of the etch pyramid initially increased with etching time, the depth eventually decreased and the density also decreased gradually, resulting in degradation in improvement effectiveness of extraction efficiency. Using the commercial PR developer for etching, however, after an initial increase in both the depth of the etch pyramid and its density, the depth and density were maintained without degradation, confirming the improvement in improvement effectiveness of extraction efficiency as well as the improvement in run to run fabrication uniformity. This may be due that with developer the GaN surface is etched only along the dislocation and is not etched over the non-defect region even as etching time goes on. [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]

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]

This review represents the last achievements in synthesis of epitaxial layers of gallium nitride (GaN) on silicon (Si) substrate. The basic physical, crystallography and physical-chemical properties of semipolar gallium nitride are described. The possible use of semipolar gallium nitride in production of devices for opto- and microelectronics is discussed. The methods of synthesis of semipolar GaN layers are considered with an emphasis on their advantages and drawbacks. Considerable attention is given to the original method of synthesis of semipolar GaN on planar Si(100), Si(210) substrates with interlayers of SiC and AlN. It is based upon the synthesis of thin SiC-layers on the surface Si(100) or Si(210) using the new method of atom substitution. Such an approach makes possible the epitaxial layers of the semipolar GaN to be synthesized on the Si substrate with deflection of the layer from the Si(100) plane by an angle ~55° and with a half-width of the X-ray diffraction rocking curve of GaN(1-101) of the order ω0~20'. [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: 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: 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]

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: 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]