GaN Powders Research Articles

High rate GaN epitaxial growth by sublimation sandwich method

Thick GaN epitaxial layers were grown by the sublimation “sandwich method” (SSM) on SiC substrates at temperatures from 1100°C to 1250°C in ammonia flow. Metallic Ga or GaN powder was used as the vapor source. The possibility of growing of monocrystalline GaN layers with growth rates as high as 1 mm/h was demonstrated. The dependence of the growth kinetics on temperature, source to substrate distance and input ammonia flow rate was studied. Various characterization techniques show the high quality of the GaN layers.

Comparison of GaN, InN and AlN powders for susceptor-based rapid annealing of group III nitride materials

We have compared the use of GaN, InN and AlN powders for providing a nitrogen partial pressure within a graphite susceptor during high-temperature rapid thermal annealing of GaN, AlN, InN and InAlN. At temperatures above vapour transport of In from InN powder produces In droplet condensation on the surface of all nitride samples being annealed. GaN powder provides better surface protection than AlN powders for temperatures up to when annealing GaN and AlN samples. Dissociation of nitrides from the surface is found to occur with approximate activation energies of 3.8 eV, 4.4 eV and 3.4 eV, respectively, for GaN, AlN and InN.

Optical metastability in bulk GaN single crystals

Bulk GaN single crystals were grown from cold pressed GaN powder by sublimation in flowing ammonia. Optical transmission measurements indicated that the absorption coefficient for the transparent samples is 50 cm−1 in the wavelength region from 650 to 400 nm. Optical metastability in bulk GaN crystals was studied through time dependent photoluminescence both at room and liquid–nitrogen temperatures. The observation included decreasing output intensity of the ultraviolet emission attributed to the band edge and increasing output intensity of a new emission band centered at 378 nm at room temperature. At liquid–nitrogen temperature, the photoinduced emission band consisted of at least one LO-phonon replica of the zero-phonon line centered at 378 nm. The ratio of output intensities of the photoinduced band to the band edge increased by a factor of 10 during 27 min of exposure time. The photoinduced effect is attributed to the metastable nature of traps in bulk GaN.

Growth and Characterization of Thermal Oxides on Gallium Nitride

ABSTRACTLittle information is available about the thermal oxidation of GaN. Since GaN is of interest for high temperature electronics, knowledge of the stability of GaN in potentially oxidizing environments would be useful. Furthermore, evaluation of the characteristics of the thermal oxide will provide information needed for assessing the potential of this oxide in processing or device applications.In this study, thick GaN epilayers and GaN powders were exposed to dry air at 450°C, 750°C, 900°C, 925°C, 950°C, and 1000°C for periods of 1 to 25 hours. Following oxidation, the epilayers were analyzed by x-ray photoelectron spectroscopy and glancing incidence x-ray diffraction, and the powders were analyzed by conventional x-ray diffraction. For both the GaN films and powders, significant oxidation was observed at 900°C, and the oxide was identified as monoclinic β-Ga2O3. Oxidation in dry air resulted in roughening of the oxide/GaN interface and oxide surface. In the temperature range 900°C to 1000°C, linear kinetics were observed for times up to 10 hours indicating an interfacial reaction mechanism as the rate limiting step for oxidation. An apparent activation energy of ∼72 kcal/mole was determined for this process.

Rapid Thermal Processing of III-Nitrides

ABSTRACTTransient thermal processing is employed for implant activation, contact alloying, implant isolation and dehydrogenation during III-nitride device fabrication. We have compared use of InN, AlN and GaN powder as methods for providing a N2 overpressure within a graphite susceptor for high temperature annealing of GaN, InN, A1N and InAlN. The AlN powder provides adequate surface protection to temperatures of ∼1100°C for AlN, > 1050°C for GaN, ∼600°C for InN and ∼800°C for the ternary alloy. While the InN powder provides a higher N2 partial pressure than AlN powder, at temperatures above ∼750°C the evaporation of In is sufficiently high to produce condensation of In droplets on the surfaces of the annealed samples. GaN powder achieved better surface protection than the other two cases.

GaN Synthesis by Ammonothermal Method

It is shown that ammonothermal method can be successfully used to synthesize GaN powder of good crystallographic quality from ammonia solution at high pressure and a moderate temperature. The size of obtained GaN powder grains was of a few micrometers. The improvement of the powder crystalline quality (examined by X-ray rocking curve, scanning electroii microscopy and luminescence measurements) with increasing molar proportion of mineralizer was observed. It was therefore possible to conclude that high molar proportion of mineralizer in ammonia solution plays a crucial role in the polycrystal growth process. Visible luminescence of high efficiency from the GaN powder was found. PACS numbers: 81.10.Dn

Study on the influence of annealing effects in GaN VPE

The effects of annealing that occur during VPE growth of GaN were investigated. GaN powder (and epilayers) samples were annealed under Ar, N 2, H 2, NH 3, HCl + N 2 and HCl + H 2 (N 2, H 2 and HCl + N 2) for a range of experimental conditions of interest for preparing electroluminescent devices. Good surface appearance Zn doped epilayers were also used N 2 in order to investigate surface morphology changes due to thermal decomposition. It was found that GaN reacts with H 2, remains stable under NH 3, and the effects of thermal decomposition are somewhat enhanced with HCl. The epilayer's behaviour under thermal decomposition and HCl are interpreted by the greater stability of the (0001) crystal plane, which accounts for the improvement of the surface quality under special growth conditions. Significant observations are reported concerning GaN decomposition in different ambients.

Refractive index of GaN

The refractive index of GaN and its temperature dependence have been measured using plane-parallel platelets with E ⊥ c. In this direction at 300 K the index is 2.67 at 3.38 eV, 2.33 at 1.0 eV, and has an extrapolated value of 2.29 ± 0.005 at 0 eV. The difference in the refractive indices for E ⊥ c and E ‖ c is 1.5 ± 0.2% at 5000 A. A Debye temperature of about 600 K is estimated from the measured temperature dependence. The diffuse reflexion spectrum of GaN powder has been measured and the temperature dependence of the absorption edge is plotted.

Influence of Oxidation Temperatures on the Structure and the Microstructure of GaN MOCVD Scraps

<p>The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200°C to 1100°C and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga<sub>2</sub>O<sub>3</sub> structure when annealed above 900°C for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.</p>