GaN Powders Research Articles

GaN Growth by Compound Source MBE Using GaN Powder

Growth of GaN at low temperatures less than 570 °C was investigated using the molecular beam epitaxy technique. GaN powder was used as a source material. The crystalline structure of GaN layers grown below 450°C was amorphous, which was estimated using RHEED patterns. Bluish-white light from the amorphous GaN layers was observed under UV light excitation at room temperature.

GaN Growth by Compound Source MBE Using GaN Powder

Growth of GaN at low temperatures less than 570 °C was investigated using the molecular beam epitaxy technique. GaN powder was used as a source material. The crystalline structure of GaN layers grown below 450 °C was amorphous, which was estimated using RHEED patterns. Bluish-white light from the amorphous GaN layers was observed under UV light excitation at room temperature.

Application of Amorphous GaN for Electroluminescence Device

AbstractThe vacuum evaporation of GaN thin films using GaN powder (5N) for GaN-based electroluminescence devices (ELDs) is reported. The crystal structures of the evaporated GaN layers were amorphous, which was confirmed from reflection high-energy electron diffraction (RHEED) patterns. Auger electron spectra revealed that the layers have excess Ga metal. Bluish-white light emission was observed from the GaN-based ELD under AC operation at RT. Although the emission intensity was weak, the electroluminescence spectra started from the band edge of h-GaN.

Structural investigation of gallium oxide (β-Ga 2O 3) nanowires grown by arc-discharge

Gallium oxide nanowires were synthesized by electric arc discharge of GaN powders mixed with a small amount of Ni and Co. The crystal structure of nanowires was determined by multi-channel X-ray diffractometry (MC-XRD), FT-Raman spectroscopy and transmission electron microscopy (TEM). The analyzed results clearly show that the synthesized nanowires are monoclinic gallium oxide (β-Ga 2O 3). Final morphology and microstructure of β-Ga 2O 3 nanowires were changed depending on the presence of the transition metals into the nanowires. The β-Ga 2O 3 nanowires grown by the assistance of transition metals demonstrate a smooth edge surface while containing twin defects at the center. The transition metals have enhanced the step growth of nanowires. However, in the case of the β-Ga 2O 3 nanowires, where the transition metals are not shown on the surface, the nanowires demonstrate rather thin and long shapes with amorphous gallium oxide layers on the nanowire surface.

Growth and microstructure of Ga 2O 3 nanorods

Gallium oxide (Ga 2O 3) nanorods were prepared by a dc arc-discharge between a graphite anode filled with a mixture of GaN, graphite and nickel powders and a graphite cathode in helium atmosphere. The structure and composition of the product were determined by high-resolution transmission electron microscopy and high spatial resolution electron energy-loss spectroscopy. The Ga 2O 3 nanorods have diameters in the range of 5–50 nm and a length of up to 30 μm. Specific features of their microstructure and the growth mechanism are discussed.

Gallium nitride quantum dots in a silica xerogel matrix

Controlled oxidation of GaN powders was performed inside xerogel cavities with the objective of demonstrating formation of composites of GaN nanoparticles embedded in a silicate matrix. A 60% reduction in GaN particle size was observed due to the oxidation of bulk particles dispersed inside the xerogel. The microstructure and phase chemistry of the nano-GaN in xerogel composite were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD).

Catalytic Growth of β-Ga2O3 Nanowires by Arc Discharge

Monoclinic gallium oxide nanowires are prepared here by arc discharge of GaN powder in the presence of a small amount of transition metal catalyst. The nanowires are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, and Raman spectroscopy, and evidence as to the mechanism of their formation (shown in the Figure) is obtained by high-resolution transmission electron microscopy.

Ammonothermal Conversion of Cyclotrigallazane to GaN: Synthesis of Nanocrystalline and Cubic GaN from [H2GaNH2]3

Under ammonothermal conditions, cyclotrigallazane, [H2GaNH2]3, was converted to nanocrystalline GaN. The coherent length of the GaN product could be controlled by manipulating reaction time and temperature. Nanocrystalline GaN powders with average crystallite sizes of 3−17 nm were produced in the temperature range of 150−450 °C. Analysis of the powders by XRD and TEM indicated that the nanocrystals possessed a structure composed of a random arrangement of cubic and hexagonal close packed planes. The addition of NH4I to the reaction mixture resulted in the isolation of bulk samples of phase pure, cubic GaN at temperatures as low as 200 °C. The synthesis of the cubic phase was found to be temperature dependent, with mixtures of cubic and hexagonal GaN being produced at temperatures greater than 350 °C.

Emission Characteristics of GaN-Based EL Device with AC Operation

ABSTRACTGaN-based electroluminescence devices (ELDs) were fabricated using a GaN powder as an emission layer. The electroluminescence spectra of the GaN ELDs under AC operation were observed at room temperature. The emission characteristics of GaN-based ELDs were studied to compare the EL spectra and the cathodoluminescence (CL) spectra. It was clarified that the EL spectra were similar to the CL spectra of a GaN emission layer. The emission peaks in the EL spectra were shifted toward the high-energy side with increasing operation frequency.

Bulk GaN single-crystals growth

Gallium nitride powder was prepared from gallium and ammonia at temperatures of 1000–1200°C. Parameters of the crystallographic lattice as well as photoluminescence and Raman spectra were determined for the obtained powder. As a result of GaN powder sublimation, GaN single crystals of 3×2×0.2 mm were received, at temperatures 1200–1250°C. Single crystals of gallium nitride were also synthesised in a reaction of gallium vapours with ammonia. Crystals up to 1.5×1×0.1 mm were obtained at the temperature range of 850–1150°C. The obtained single crystals were studied by X-ray methods resulting in structure refining, mapping of reflexes and rocking curves. In addition, Raman spectroscopy studies and conductivity measurements were carried out. It was also demonstrated that the crystallographic structure of the crystals and powders was well pronounced. Homoepitaxial GaN films of several tens of micrometers were deposited onto selected GaN single crystals. The influence of grain size on the GaN sublimation process was studied. The 50–500 μm GaN crystalline powder sublimation resulted in the growth of single crystals whose quality was significantly better in comparison to effects of the sublimation of a few micrometer crystalline powder.

Vapor Phase Synthesis and Characterization of Gallium Nitride Powders

ABSTRACTGaN crystalline powders have been synthesized by the reaction of a Ga vapor with an ammonia gas at the reaction temperature Tr = 900 - 1100°C in an atmospheric-pressure open-tube reactor. The size of GaN particles ranges from 0.2 to 2νm. It was found that the structural and luminescent properties depend strongly on Tr. The mean size of the GaN particles increased as Tr is raised. The GaN powders exhibited photoluminescence (PL) dominated by the band edge emissions. Thermal quenching is relatively significant for the powders synthesized at lower Tr. This is presumably due to enhanced non-radiative recombination at the surface because of their smaller particle size.

Growth of AlN and GaN Thin Films on Si(100) Using New Single Molecular Precursors by MOCVD Method

Thin films of hexagonal AlN and GaN have been deposited on Si(100) substrates by MOCVD in the temperature range of 650 to 850 °C using cyclic diethylaluminium amide (DEAA), bis [diethyl(t-butylamido)aluminium] (DETBAA), cyclic dimethylgallium amide (DMGA), and bis [diethyl(t-butylamido)gallium] (DETBAG), as new single molecular precursors. On Si(100) at temperatures as low as 750 °C, strong preferential growth of hexagonal GaN(0002) thin films were successfully grown from DMGA without carrier gas. In the case of AlN film growth, however, only polycrystalline h-AlN thin films were obtained at temperatures above 750 °C using the precursors of DEAA and DETBAA. The XP spectra of all deposited AlN and GaN films are indistinguishable from that of AlN and GaN powders, and the Auger depth profile confirms that the films are stoichiometric and do not contain an appreciable amount of carbon. This is the first report on the growth of the h-GaN films from the synthesized precursors of DMGA and DETBAG, and we investigated their physical properties by nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and gas chromatography (GC).

Thermodynamic calculation of the binary systems M-Ga and investigation of ternary M-Ga-N phase equilibria (M=Ni, Co, Pd, Cr)

A thermodynamic modeling of the binary systems Ni-Ga, Co-Ga, Pd-Ga, and Cr-Ga has been performed using the CALPHAD method. This modeling is focused on a simplified description of the solid-state equilibria. From published data on binary nitrogen systems, isothermal sections of the ternary M-Ga-N systems have been calculated by extrapolation. Ternary samples were prepared from M and GaN powders in various ratios, pressed to pellets, and annealed between 500 and 700 °C for up to 162 h. Phase analyses were carried out by x-ray diffraction, and the results compared to the calculated ternary phase equilibria; the comparisons indicate that M+GaN are not in equilibrium in any of these systems. Experimental results show that the M+GaN reactions are sluggish. In the ternary Ni-, Co-, and Pd-Ga-N systems, no ternary compounds were observed. The solid reaction products are essentially the metal-rich binary intermetallics (Ni3Ga, CoGa, Pd2Ga). Thermodynamic calculations show that, at elevated (local) pressure, reaction slows down. Pressure buildup must have occurred inside the tightly pressed pellet, since only small amounts of nitrogen gas were found to have escaped from the pellet. In the Cr-Ga-N system, two ternary compounds are known to exist along the Cr-GaN section. Therefore, the reaction of GaN with Cr to form the ternary phases could occur without gas liberation. Even this reaction is sluggish and was not completed in the samples investigated.

The emission spectrum of pulsed laser deposited GaN and its powder precursor

Thin films of wurtzite GaN have been grown on heated sapphire substrates in reactive atmospheres of nitrogen or ammonia by pulsed laser deposition (PLD) using KrF excimer laser ablation of compressed and sintered powder targets of GaN. We report here a comparative study of the films and their powder precursor by means of low temperature photoluminescence (PL) spectroscopy, cathodoluminescence (CL) imaging and scanning electron microscopy (SEM). GaN powder manufactured by Cerac shows several well-defined PL features. Although the free exciton is absent, two relatively sharp bands appear at 3.461 and 3.410 eV, in addition to the familiar donor-acceptor pair band near 3.2 eV and the well-known yellow band. SEM imaging reveals relatively poor crystallinity in the micropowder. PLD films prepared from the Cerac powder show a completely different set of sharp features, between 3.360 and 3.160 eV. Thus it is clear that PLD is not just a means of stoichiometric material transfer, but also leads to modification of structural and electronic properties. The spectroscopy of these sharp lines, observed previously in GaN samples prepared by vapour phase epitaxial techniques, provides some interesting clues to their origin.

Epitaxial growth of nitride semiconductor films by laser ablation

GaN epitaxial films on (0001) sapphire substrates were fabricated by laser ablation, An ArF excimer laser (193 nm, 25 ns) with an energy of 140 ml/pulse was used for ablating cold-pressed GaN targets made from high-purity GaN powders. Just before the deposition, thermal cleaning of the substrate surface at 1073 K was essential. The substrate temperature was varied between 873 and 1073 K, Above 973 K, the epitaxial layers were obtained, When a buffer layer of GaN was deposited at lower temperatures before the epitaxial growth, the crystalline quality and surface morphology were greatly improved.

Wet thermal oxidation of GaN

Thermal oxidation of GaN was conducted at 700–900°C with O2, N2, and Ar as carrier gases for 525–630 Torr of H2O vapor. Upon oxidation of both GaN powders and n-GaN epilayers, the monoclinic β-Ga2O3 phase was identified using glancing angle x-ray diffraction. The chemical composition of the oxide was verified using x-ray photoelectron spectroscopy. In experiments conducted using GaN powder, the oxide grew most rapidly when O2 was the carrier gas for H2O. The same result was obtained on n-type GaN epilayers. Furthermore, the thickness of the oxide grown in H2O with O2 as the carrier gas was found to be proportional to the oxidation time at all temperatures studied, and an activation energy of 210±10 kJ/mol was obtained. Scanning electron microscopy revealed a smoother surface after wet oxidation than was reported previously for dry oxidation. However, cross-sectional transmission electron microscopy revealed that the wet oxide/GaN interface was irregular and non-ideal for devicefabrication, even more so than the dry oxide/GaN interface. This observation was consistent with poor electrical properties.

An IR Spectroscopic Investigation of Nanostructured AlN and GaN Powder Surfaces

By combining the results of IR spectroscopy experiments, both in the transmission and diffuse reflectance modes, with data obtained by HRTEM, XRD and XPS an overall picture of AlN and GaN nanoparticle surface structures and functionality were deduced. The surface species from the IR data analysis indicated that the nanostructured AlN powder surfaces had acidic and weak basic sites in the form of Al3+ and Al3N−, respectively. Also present were -OH, -NH2, and -NH. For GaN, the bulk core of the particle had a zincblendel (FCC) structure with nitrogen vacancies, and the only functionality detected was Ga–H. The surface of the particles had a wurtzite(HCP) structure, with abundant NH and NH2 groups as well as OH and Ga3+ functionalities.

ARC Discharge for the Synthesis of Monoclinic Ga2O3 Nanowires

ABSTRACTMonoclinic gallium oxide (β-Ga2O3) nanowires were catalytically synthesized by electric arc discharge of GaN powders mixed with a small amount (less than 5 %) of transition metals under a pressure of 500 Torr (80 %-Ar + 20 %-O2). Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images showed that the average diameter of the wires were about 30 nm and their lengths were as long as up to one hundred micrometer, resulting in extremely large aspect ratio. Fourier diffractogram was indicative of single crystalline nature of the β-Ga2O3 wire. HRTEM image also showed β-Ga2O3 with twin defects at the center of the wire which might play as nucleation seeds. Both X-ray diffraction (XRD) patterns and FT-Raman spectra of the wires identified the observed nanowires as monoclinic crystalline gallium oxides.

Phonon density of states of bulk gallium nitride

We report the measured phonon density of states of a bulk GaN powder by time-of-flight neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45–65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model.

Kinetic Study of the Oxidation of Gallium Nitride in Dry Air

The oxidation of polycrystalline GaN powder and GaN epi layers in dry air has been investigated. Bulk θ‐2θ X‐ray diffraction (XRD) revealed no evidence of oxide formation on the powder specimen exposed to temperatures of up to 750 °C for 25 h However, when oxidized at temperatures of 900 °C or greater for 1 h or longer, an oxide was observed to form and was identified as the monoclinic , the same oxide observed previously by the present investigators to form on epitaxial GaN films. Information regarding the oxidation kinetics was obtained in the present study by measuring the intensity of the , (2¯ 1 7) XRD peak as a function of oxidation time at various temperatures, and the initial stage of the oxidation was found to be limited by the rate of an interfacial reaction with an activation energy of ∼3 × 105 J/mol. An interfacial reaction‐controlled mechanism was also observed to limit the rate of oxidation of GaN epi layers at 900 °C.