Effects of Precursor-Substrate Distances on the Growth of GaN Nanowires

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Hongbin Cheng

2015-01-01

Full Text Available GaN nanowires were synthesized through the Ni-catalyzed chemical vapor deposition (CVD method using Ga2O3/GaN mixtures as gallium sources, and precursor-substrate distances were investigated as the important factor for the growth of GaN nanowires. The microstructure, composition, and photoluminescence property were characterized by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra. The results showed that single crystalline GaN nanowires with the diameter of about 90 nm and the length up to tens of micrometers had been grown thickly across Si (100 substrates with uniform density. Moreover, the variations of the GaN nanowire morphology, density, and size were largely attributed to substrate positions which would influence Ga precursor density in the carrier gas, the saturation degree of gaseous reactants, and the catalyst activity, respectively, in the fabrication of GaN nanowires by the vapour liquid solid mechanism.

Material development for grade X80 heavy-wall hot induction bends

International Nuclear Information System (INIS)

Wang Xu; Xiao Furen; Fu Yanhong; Chen Xiaowei; Liao Bo

2011-01-01

Highlights: ► The new material for X80 heavy wall thickness hot induction bend was designed. ► The continuous cooling transformation (CCT) diagrams were determined. ► The steel adapts to manufacture of X80 heavy-wall thickness hot induction bend. ► The optimum manufactural processes were obtained. ► The bending temperature is about 990 °C, and tempering is about 600 °C. - Abstract: A new steel for grade X80 heavy wall thickness hot induction bends was designed based on the chemical compositions of commercial X80 steels in this work. Then, its continuous cooling transformation (CCT) diagram was determined with Gleeble-3500 thermo-mechanical simulator. Furthermore, the effects of heat treatment technology on its microstructure and mechanical property were investigated, and the technology parameters of the heat treatment were optimized. The results show that the acicular ferrite and/or bainite transformations are promoted, the polygonal ferrite and pearlite transformation are restrained, because proper amount of alloying elements were added into the new steel. Therefore, the strength of this new steel is improved markedly, even if the cooling rate is lower, which ensure the higher strength distribution along cross section of the heavy wall thickness. It is significant for the manufacture of grade X80 heavy wall thickness hot induction bends in the second West-to-East gas transportation pipeline project of China.

Development of laser-fired contacts for amorphous silicon layers obtained by Hot-Wire CVD

International Nuclear Information System (INIS)

Munoz, D.; Voz, C.; Blanque, S.; Ibarz, D.; Bertomeu, J.; Alcubilla, R.

2009-01-01

In this work we study aluminium laser-fired contacts for intrinsic amorphous silicon layers deposited by Hot-Wire CVD. This structure could be used as an alternative low temperature back contact for rear passivated heterojunction solar cells. An infrared Nd:YAG laser (1064 nm) has been used to locally fire the aluminium through the thin amorphous silicon layers. Under optimized laser firing parameters, very low specific contact resistances (ρ c ∼ 10 mΩ cm 2 ) have been obtained on 2.8 Ω cm p-type c-Si wafers. This investigation focuses on maintaining the passivation quality of the interface without an excessive increase in the series resistance of the device.

Material development for grade X80 heavy-wall hot induction bends

Energy Technology Data Exchange (ETDEWEB)

Wang Xu [Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); CNPC Bohai Petroleum Equipment Manufacture Co. Ltd., Qingxian 062658 (China); Xiao Furen, E-mail: frxiao@ysu.edu.cn [Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); Fu Yanhong [CNPC Bohai Petroleum Equipment Manufacture Co. Ltd., Qingxian 062658 (China); Chen Xiaowei [Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004 (China); CNPC Bohai Petroleum Equipment Manufacture Co. Ltd., Qingxian 062658 (China); Liao Bo, E-mail: cyddjyjs@263.net [Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao 066004 (China)

2011-12-15

Highlights: Black-Right-Pointing-Pointer The new material for X80 heavy wall thickness hot induction bend was designed. Black-Right-Pointing-Pointer The continuous cooling transformation (CCT) diagrams were determined. Black-Right-Pointing-Pointer The steel adapts to manufacture of X80 heavy-wall thickness hot induction bend. Black-Right-Pointing-Pointer The optimum manufactural processes were obtained. Black-Right-Pointing-Pointer The bending temperature is about 990 Degree-Sign C, and tempering is about 600 Degree-Sign C. - Abstract: A new steel for grade X80 heavy wall thickness hot induction bends was designed based on the chemical compositions of commercial X80 steels in this work. Then, its continuous cooling transformation (CCT) diagram was determined with Gleeble-3500 thermo-mechanical simulator. Furthermore, the effects of heat treatment technology on its microstructure and mechanical property were investigated, and the technology parameters of the heat treatment were optimized. The results show that the acicular ferrite and/or bainite transformations are promoted, the polygonal ferrite and pearlite transformation are restrained, because proper amount of alloying elements were added into the new steel. Therefore, the strength of this new steel is improved markedly, even if the cooling rate is lower, which ensure the higher strength distribution along cross section of the heavy wall thickness. It is significant for the manufacture of grade X80 heavy wall thickness hot induction bends in the second West-to-East gas transportation pipeline project of China.

Menopausal Hot Flashes and White Matter Hyperintensities

Science.gov (United States)

Thurston, Rebecca C.; Aizenstein, Howard J.; Derby, Carol A.; Sejdić, Ervin; Maki, Pauline M.

2015-01-01

Objective Hot flashes are the classic menopausal symptom. Emerging data links hot flashes to cardiovascular disease (CVD) risk, yet how hot flashes are related to brain health is poorly understood. We examined the relationship between hot flashes - measured via physiologic monitor and self-report - and white matter hyperintensities (WMH) among midlife women. Methods Twenty midlife women ages 40-60 without clinical CVD, with their uterus and both ovaries, and not taking hormone therapy were recruited. Women underwent 24 hours of ambulatory physiologic and diary hot flash monitoring to quantify hot flashes; magnetic resonance imaging to assess WMH burden; 72 hours of actigraphy and questionnaires to quantify sleep; and a blood draw, questionnaires, and physical measures to quantify demographics and CVD risk factors. Test of a priori hypotheses regarding relations between physiologically-monitored and self-reported wake and sleep hot flashes and WMH were conducted in linear regression models. Results More physiologically-monitored hot flashes during sleep were associated with greater WMH, controlling for age, race, and body mass index [beta(standard error)=.0002 (.0001), p=.03]. Findings persisted controlling for sleep characteristics and additional CVD risk factors. No relations were observed for self-reported hot flashes. Conclusions More physiologically-monitored hot flashes during sleep were associated with greater WMH burden among midlife women free of clinical CVD. Results suggest that relations between hot flashes and CVD risk observed in the periphery may extend to the brain. Future work should consider the unique role of sleep hot flashes in brain health. PMID:26057822

Hot-wall corrosion testing of simulated high level nuclear waste

International Nuclear Information System (INIS)

Chandler, G.T.; Zapp, P.E.; Mickalonis, J.I.

1995-01-01

Three materials of construction for steam tubes used in the evaporation of high level radioactive waste were tested under heat flux conditions, referred to as hot-wall tests. The materials were type 304L stainless steel alloy C276, and alloy G3. Non-radioactive acidic and alkaline salt solutions containing halides and mercury simulated different high level waste solutions stored or processed at the United States Department of Energy's Savannah River Site. Alloy C276 was also tested for corrosion susceptibility under steady-state conditions. The nickel-based alloys C276 and G3 exhibited excellent corrosion resistance under the conditions studied. Alloy C276 was not susceptible to localized corrosion and had a corrosion rate of 0.01 mpy (0.25 μm/y) when exposed to acidic waste sludge and precipitate slurry at a hot-wall temperature of 150 degrees C. Type 304L was susceptible to localized corrosion under the same conditions. Alloy G3 had a corrosion rate of 0.1 mpy (2.5 μm/y) when exposed to caustic high level waste evaporator solution at a hot-wall temperature of 220 degrees C compared to 1.1 mpy (28.0 μ/y) for type 304L. Under extreme caustic conditions (45 weight percent sodium hydroxide) G3 had a corrosion rate of 0.1 mpy (2.5 μm/y) at a hot-wall temperature of 180 degrees C while type 304L had a high corrosion rate of 69.4 mpy (1.8 mm/y)

Application of CVD diamond film for radiation detection

International Nuclear Information System (INIS)

Zhou Haiyang; Zhu Xiaodong; Zhan Rujuan

2005-01-01

With the development of diamond synthesis at low pressure, the CVD diamond properties including electronic characteristics have improved continuously. Now the fabrication of electronic devices based on the CVD diamond has been one of hot research subjects in this field. Due to many unique advantages, such as high signal-noise ratio, fast time response, and normal output in extremely harsh surrounding, the CVD diamond radiation detector has attracted more and more interest. In this paper, we have reviewed the development and status of the CVD diamond radiation detector. The prospect of this detector is described. (authors)

Characterization of remote O2-plasma-enhanced CVD SiO2/GaN(0001) structure using photoemission measurements

Science.gov (United States)

Truyen, Nguyen Xuan; Ohta, Akio; Makihara, Katsunori; Ikeda, Mitsuhisa; Miyazaki, Seiichi

2018-01-01

The control of chemical composition and bonding features at a SiO2/GaN interface is a key to realizing high-performance GaN power devices. In this study, an ∼5.2-nm-thick SiO2 film has been deposited on an epitaxial GaN(0001) surface by remote O2-plasma-enhanced chemical vapor deposition (O2-RPCVD) using SiH4 and Ar/O2 mixture gases at a substrate temperature of 500 °C. The depth profile of chemical structures and electronic defects of the O2-RPCVD SiO2/GaN structures has been evaluated from a combination of SiO2 thinning examined by X-ray photoelectron spectroscopy (XPS) and the total photoelectron yield spectroscopy (PYS) measurements. As a highlight, we found that O2-RPCVD is effective for fabricating an abrupt SiO2/GaN interface.

Menopausal Hot Flashes and Carotid Intima Media Thickness Among Midlife Women.

Science.gov (United States)

Thurston, Rebecca C; Chang, Yuefang; Barinas-Mitchell, Emma; Jennings, J Richard; Landsittel, Doug P; Santoro, Nanette; von Känel, Roland; Matthews, Karen A

2016-12-01

There has been a longstanding interest in the role of menopause and its correlates in the development of cardiovascular disease (CVD) in women. Menopausal hot flashes are experienced by most midlife women; emerging data link hot flashes to CVD risk indicators. We tested whether hot flashes, measured via state-of-the-art physiologic methods, were associated with greater subclinical atherosclerosis as assessed by carotid ultrasound. We considered the role of CVD risk factors and estradiol concentrations in these associations. A total of 295 nonsmoking women free of clinical CVD underwent ambulatory physiologic hot flash assessments; a blood draw; and carotid ultrasound measurement of intima media thickness and plaque. Associations between hot flashes and subclinical atherosclerosis were tested in regression models controlling for CVD risk factors and estradiol. More frequent physiologic hot flashes were associated with higher carotid intima media thickness (for each additional hot flash: β [SE]=0.004 [0.001]; P=0.0001; reported hot flash: β [SE]=0.008 [0.002]; P=0.002, multivariable) and plaque (eg, for each additional hot flash, odds ratio [95% confidence interval] plaque index ≥2=1.07 [1.003-1.14]; P=0.04, relative to no plaque, multivariable] among women reporting daily hot flashes; associations were not accounted for by CVD risk factors or by estradiol. Among women reporting hot flashes, hot flashes accounted for more variance in intima media thickness than most CVD risk factors. Among women reporting daily hot flashes, frequent hot flashes may provide information about a woman's vascular status beyond standard CVD risk factors and estradiol. Frequent hot flashes may mark a vulnerable vascular phenotype among midlife women. © 2016 American Heart Association, Inc.

Evaluation of Tritium Behavior in the Epoxy Painted Concrete Wall of ITER Hot Cell

International Nuclear Information System (INIS)

Nakamura, Hirofumi; Hayashi, Takumi; Kobayashi, Kazuhiro; Nishi, Masataka

2005-01-01

Tritium behavior released in the ITER hot cell has been investigated numerically using a combined analytical methods of a tritium transport analysis in the multi-layer wall (concrete and epoxy paint) with the one dimensional diffusion model and a tritium concentration analysis in the hot cell with the complete mixing model by the ventilation. As the results, it is revealed that tritium concentration decay and permeation issues are not serious problem in a viewpoint of safety, since it is expected that tritium concentration in the hot cell decrease rapidly within several days just after removing the tritium release source, and tritium permeation through the epoxy painted concrete wall will be negligible as long as the averaged realistic diffusion coefficient is ensured in the concrete wall. It is also revealed that the epoxy paint on the concrete wall prevents the tritium inventory increase in the concrete wall greatly (two orders of magnitudes), but still, the inventory in the wall is estimated to reach about 0.1 PBq for 20 years operation

Undoped CVD diamond films for electrochemical applications

International Nuclear Information System (INIS)

Mosinska, Lidia; Fabisiak, Kazimierz; Paprocki, Kazimierz; Kowalska, Magdalena; Popielarski, Pawel; Szybowicz, Miroslaw

2013-01-01

By using different deposition conditions, the CVD diamond films with different qualities and orientation were grown by the hot-filament CVD technique. The object of this article is to summarize and discuss relation between structural, physical and electrochemical properties of different diamond electrodes. The physical properties of the Hot Filament CVD microcrystalline diamond films are analyzed by scanning electron microscopy and Raman spectroscopy. In presented studies two different electrodes were used of the diamond grain sizes around 200 nm and 10 μm, as it was estimated from SEM picture. The diamond layers quality was checked on basis of FWHM (Full width at Half Maximum) of 1332 cm −1 diamond Raman peak. The ratio of sp 3 /sp 2 carbon bonds was determined by 1550 cm −1 G band and 1350 cm −1 D band in the Raman spectrum. The electrochemical properties were analyzed using (CV) cyclic voltammetry measurements in aqueous solutions. The sensitivity of undoped diamond electrodes depends strongly on diamond film quality and concentration of amorphous carbon phase in the diamond layer

Selective tungsten deposition in a batch cold wall CVD system

International Nuclear Information System (INIS)

Chow, R.; Kang, S.; Harshbarger, W.R.; Susoeff, M.

1987-01-01

Selective deposition of tungsten offers many advantages for VLSI technology. The process can be used as a planarization technique for multilevel interconnect technology, it can be used to fill contacts and to provide a barrier layer between Al and Si materials, and the selective W process might be used as a self-aligned technology to provide low resistance layers on source/drain and gate conductors. Recent publications have indicate that cold wall CVD systems provide advantages for development of selective W process. Genus has investigated selective W deposition processing, and we have developed a selective W deposition process for the Genus 8402 multifilm deposition system. This paper describes the Genus 8402 system and the selective W process developed in this reactor. To further develop selective W technology, Genus has signed an agreement with General Electric establishing a joint development program. As a part of this program, the authors characterized the selective W process for encroachment, Si consumption and degrees of selectivity on various dielectrics. The status of this development activity and process characterization is reviewed in this paper

CVD diamond for nuclear detection applications

CERN Document Server

Bergonzo, P; Tromson, D; Mer, C; Guizard, B; Marshall, R D; Foulon, F

2002-01-01

Chemically vapour deposited (CVD) diamond is a remarkable material for the fabrication of radiation detectors. In fact, there exist several applications where other standard semiconductor detectors do not fulfil the specific requirements imposed by corrosive, hot and/or high radiation dose environments. The improvement of the electronic properties of CVD diamond has been under intensive investigations and led to the development of a few applications that are addressing specific industrial needs. Here, we report on CVD diamond-based detector developments and we describe how this material, even though of a polycrystalline nature, is readily of great interest for applications in the nuclear industry as well as for physics experiments. Improvements in the material synthesis as well as on device fabrication especially concern the synthesis of films that do not exhibit space charge build up effects which are often encountered in CVD diamond materials and that are highly detrimental for detection devices. On a pre-i...

Hydride vapor phase epitaxy growth of GaN, InGaN, ScN, and ScAIN

NARCIS (Netherlands)

Bohnen, T.

2010-01-01

Chemical vapor deposition (CVD); hydride vapor phase epitaxy (HVPE); gallium nitride (GaN); indium gallium nitride (InGaN); scandium nitride (ScN); scandium aluminum nitride (ScAlN); semiconductors; thin films; nanowires; III nitrides; crystal growth - We studied the HVPE growth of different III

CVD-grown horizontally aligned single-walled carbon nanotubes: synthesis routes and growth mechanisms.

Science.gov (United States)

Ibrahim, Imad; Bachmatiuk, Alicja; Warner, Jamie H; Büchner, Bernd; Cuniberti, Gianaurelio; Rümmeli, Mark H

2012-07-09

Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct growth of freestanding GaN on C-face SiC by HVPE.

Science.gov (United States)

Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

2015-06-02

In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra.

The study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 steel under hot and cold wall conditions

International Nuclear Information System (INIS)

Maniee, A.; Mahboubi, F.; Soleimani, R.

2014-01-01

Highlights: • 34CrNiMo6 steel was plasma nitrided under hot and cold wall conditions. • The amount of ε phase in hot wall condition was more than that of cold wall condition. • Wear resistance of hot wall nitrided samples was more than cold wall treated ones. • Hot wall nitriding provides better corrosion behavior than cold wall nitriding. - Abstract: This paper reports on a comparative study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 low alloy steel under modern hot wall condition and conventional cold wall condition. Plasma nitriding was carried out at 500 °C and 550 °C with a 25% N 2 + 75% H 2 gas mixture for 8 h. The wall temperature of the chamber in hot wall condition was set to 400 °C. The treated specimens were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness and surface roughness techniques. The wear test was performed by pin-on-disc method. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were also used to evaluate the corrosion resistance of the samples. The results demonstrated that in both nitriding conditions, wear and corrosion resistance of the treated samples decrease with increasing temperature from 500 °C to 550 °C. Moreover, nitriding under hot wall condition at the same temperature provided slightly better tribological and corrosion behavior in comparison with cold wall condition. In consequence, the lowest friction coefficient, and highest wear and corrosion resistance were found on the sample treated under hot wall condition at 500 °C, which had the maximum surface hardness and ε-Fe 2–3 N phase

Study of the structural evolutions of crystalline tungsten oxide films prepared using hot-filament CVD

International Nuclear Information System (INIS)

Feng, P X; Wang, X P; Zhang, H X; Yang, B Q; Wang, Z B; Gonzalez-BerrIos, A; Morell, G; Weiner, B

2007-01-01

Structural evolutions of tungsten oxide(WO 3 ) samples on different substrates are studied using Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The WO 3 samples are prepared using hot-filament CVD techniques. The focus of the study is on the evolutions of nano structures at different stages following deposition time. The experimental measurements reveal evolutions of the surface structures from uniform film to fractal-like structures, and eventually to nano particles, and crystalline structures from mono (0 1 0) crystalline thin film to polycrystalline thick film developments. The effect of high temperature on the nanostructured WO 3 is also investigated. Well-aligned nanoscale WO 3 rod arrays are obtained at a substrate temperature of up to 1400 deg. C. Further increasing the substrate temperature yields microscale crystalline WO 3 particles

The versatility of hot-filament activated chemical vapor deposition

International Nuclear Information System (INIS)

Schaefer, Lothar; Hoefer, Markus; Kroeger, Roland

2006-01-01

In the field of activated chemical vapor deposition (CVD) of polycrystalline diamond films, hot-filament activation (HF-CVD) is widely used for applications where large deposition areas are needed or three-dimensional substrates have to be coated. We have developed processes for the deposition of conductive, boron-doped diamond films as well as for tribological crystalline diamond coatings on deposition areas up to 50 cm x 100 cm. Such multi-filament processes are used to produce diamond electrodes for advanced electrochemical processes or large batches of diamond-coated tools and parts, respectively. These processes demonstrate the high degree of uniformity and reproducibility of hot-filament CVD. The usability of hot-filament CVD for diamond deposition on three-dimensional substrates is well known for CVD diamond shaft tools. We also develop interior diamond coatings for drawing dies, nozzles, and thread guides. Hot-filament CVD also enables the deposition of diamond film modifications with tailored properties. In order to adjust the surface topography to specific applications, we apply processes for smooth, fine-grained or textured diamond films for cutting tools and tribological applications. Rough diamond is employed for grinding applications. Multilayers of fine-grained and coarse-grained diamond have been developed, showing increased shock resistance due to reduced crack propagation. Hot-filament CVD is also used for in situ deposition of carbide coatings and diamond-carbide composites, and the deposition of non-diamond, silicon-based films. These coatings are suitable as diffusion barriers and are also applied for adhesion and stress engineering and for semiconductor applications, respectively

Low temperature CVD deposition of silicon carbide

International Nuclear Information System (INIS)

Dariel, M.; Yeheskel, J.; Agam, S.; Edelstein, D.; Lebovits, O.; Ron, Y.

1991-04-01

The coating of graphite on silicon carbide from the gaseous phase in a hot-well, open flow reactor at 1150degC is described. This study constitutes the first part of an investigation of the process for the coating of nuclear fuel by chemical vapor deposition (CVD)

CVD diamond for nuclear detection applications

International Nuclear Information System (INIS)

Bergonzo, P.; Brambilla, A.; Tromson, D.; Mer, C.; Guizard, B.; Marshall, R.D.; Foulon, F.

2002-01-01

Chemically vapour deposited (CVD) diamond is a remarkable material for the fabrication of radiation detectors. In fact, there exist several applications where other standard semiconductor detectors do not fulfil the specific requirements imposed by corrosive, hot and/or high radiation dose environments. The improvement of the electronic properties of CVD diamond has been under intensive investigations and led to the development of a few applications that are addressing specific industrial needs. Here, we report on CVD diamond-based detector developments and we describe how this material, even though of a polycrystalline nature, is readily of great interest for applications in the nuclear industry as well as for physics experiments. Improvements in the material synthesis as well as on device fabrication especially concern the synthesis of films that do not exhibit space charge build up effects which are often encountered in CVD diamond materials and that are highly detrimental for detection devices. On a pre-industrial basis, CVD diamond detectors have been fabricated for nuclear industry applications in hostile environments. Such devices can operate in harsh environments and overcome limitations encountered with the standard semiconductor materials. Of these, this paper presents devices for the monitoring of the alpha activity in corrosive nuclear waste solutions, such as those encountered in nuclear fuel assembly reprocessing facilities, as well as diamond-based thermal neutron detectors exhibiting a high neutron to gamma selectivity. All these demonstrate the effectiveness of a demanding industrial need that relies on the remarkable resilience of CVD diamond

Wall shear stress hot film sensor for use in gases

International Nuclear Information System (INIS)

Osorio, O D; Silin, N

2011-01-01

The purpose of this work is to present the construction and characterization of a wall shear stress hot film sensor for use in gases made with MEMS technology. For this purpose, several associated devices were used, including a constant temperature feedback bridge and a shear stress calibration device that allows the sensor performance evaluation. The sensor design adopted here is simple, economical and is manufactured on a flexible substrate allowing its application to curved surfaces. Stationary and transient wall shear stress tests were carried on by means of the calibration device, determining its performance for different conditions.

Comparative evaluation of CVD diamond technologies

Energy Technology Data Exchange (ETDEWEB)

Anthony, T.R. [General Electric Corporate Research & Development Center, Schenectady, NY (United States)

1993-01-01

Chemical vapor deposition (CVD) of diamonds occurs from hydrogen-hydrocarbon gas mixtures in the presence of atomic hydrogen at subatmospheric pressures. Most CVD methods are based on different means of generating and transporting atomic hydrogen in a particular system. Evaluation of these different techniques involves their capital costs, material costs, energy costs, labor costs and the type and quality of diamond that they produce. Currently, there is no universal agreement on which is the best technique and technique selection has been largely driven by the professional background of the user as well as the particular application of interest. This article discusses the criteria for evaluating a process for low-pressure deposition of diamond. Next, a brief history of low-pressure diamond synthesis is reviewed. Several specific processes are addressed, including the hot filament process, hot filament electron-assisted chemical vapor deposition, and plasma generation of atomic hydrogen by glow discharge, microwave discharge, low pressure radio frequency discharge, high pressure DC discharge, high pressure microwave discharge jets, high pressure RF discharge, and high and low pressure flames. Other types of diamond deposition methods are also evaluated. 101 refs., 15 figs.

Atomic structures and mechanical properties of single-crystal GaN nanotubes

International Nuclear Information System (INIS)

Xu, B.; Lu, A.J.; Pan, B.C.; Yu, Q.X.

2005-01-01

An approach is proposed to theoretically construct a realistic single-crystal GaN nanotube at atomic scale. The generated atomic structures of the single-crystal GaN nanotubes match the structural aspects from experiment very well. Our energetic calculations show that a single-crystal GaN nanotube with [100]-oriented lateral facets is more stable than that with [110]-oriented lateral facets, when they have around the same wall thickness. For a specified orientation of the lateral facets on the single-crystal GaN nanotubes, the energetic stabilities of the tubes obey a P rule, in which P is the ratio of the number of four-coordinated atoms to the number of three-coordinated atoms. Furthermore, the Young's modulus of the considered GaN nanotubes decrease with increasing the ratio of the number of bulk atoms to the number of surface atoms in each type of tube. Our calculations and analysis demonstrate that the surface effect of a single-crystal nanotube enhances its Young's modulus significantly

Unstable behaviour of normally-off GaN E-HEMT under short-circuit

Science.gov (United States)

Martínez, P. J.; Maset, E.; Sanchis-Kilders, E.; Esteve, V.; Jordán, J.; Bta Ejea, J.; Ferreres, A.

2018-04-01

The short-circuit capability of power switching devices plays an important role in fault detection and the protection of power circuits. In this work, an experimental study on the short-circuit (SC) capability of commercial 600 V Gallium Nitride enhancement-mode high-electron-mobility transistors (E-HEMT) is presented. A different failure mechanism has been identified for commercial p-doped GaN gate (p-GaN) HEMT and metal-insulator-semiconductor (MIS) HEMT. In addition to the well known thermal breakdown, a premature breakdown is shown on both GaN HEMTs, triggered by hot electron trapping at the surface, which demonstrates that current commercial GaN HEMTs has requirements for improving their SC ruggedness.

Low-pressure c-BN deposition - is a CVD process possible?

International Nuclear Information System (INIS)

Haubner, R.; Tang, X.

2001-01-01

Since the low-pressure diamond deposition was discovered in 1982 there is a high interest to find a similar process for the c-BN synthesis. A review about the c-BN deposition process as well as its characterization is given. Experiments with a simple chemical vapor deposition(CVD) reactor using tris(dimethylamino)borane as precursor were carried out. In a cold-wall reactor substrates were heated up by high-frequency. Argon was used as protecting and carrying the precursor, it was saturated with tris(dimethylamino)borane (precursor) according to its vapor pressure and transports the pressure to the hot substrate, where deposition occurs. WC-Co hardmetal plates containing 6 wt. % Co, Mo and Si were used as substrates. Various BN layers were deposited and characterized. X-ray diffraction, IR-spectroscopy and SIMS indicate that BN-coatings containing c-BN were deposited. However a final verification of c-BN crystallites by TEM investigations was not possible till now. (nevyjel)

CVD refractory metals and alloys for space nuclear power application

International Nuclear Information System (INIS)

Yang, L.; Gulden, T.D.; Watson, J.F.

1984-01-01

CVD technology has made significant contributions to the development of space nuclear power systems during the period 1962 to 1972. For the in-core thermionic concept, CVD technology is essential to the fabrication of the tungsten electron emitter. For the liquid metal cooled fuel pin using uranium nitride as fuel and T-111 and Nb-1 Zr as cladding, a tungsten barrier possibly produced by CVD methods is essential to the fuel-cladding compatibility at the designed operating temperature. Space power reactors may use heat pipes to transfer heat from the reactor core to the conversion system. CVD technology has been used for fabricating the heat pipe used as cross-flow heat exchanger, including the built-in channels on the condenser wall for liquid lithium return. 28 references, 17 figures

Doping of GaN by ion implantation: Does It Work?

International Nuclear Information System (INIS)

Suvkhanov, A.; Wu, W.; Price, K.; Parikh, N.; Irene, E.; Hunn, J.; Thomson, D.; Davis, R.F.; Krasnobaev, L.

1998-04-01

Epitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si + (for n-type) and 80 keV Mg + (for p-type) with various fluences from 1 x 10 12 to 7 x 10 15 ions/cm 2 at liquid nitrogen temperature (LT), room temperature (RT), and 700 C (HT). High temperature (1,200 C and 1,500 C) annealing was carried out after capping the GaN with epitaxial AlN by MOCVD to study damage recovery. Samples were capped by a layer of AlN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 C decrease the lattice disorder; hot implants above 550 C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg + (5 x 10 14 cm 2 ) implanted and annealed GaN showed two peaks: one ∼ 100 meV and another ∼ 140 meV away from the band edge

Ternary Precursors for Depositing I-III-VI2 Thin Films for Solar Cells via Spray CVD

Science.gov (United States)

Banger, K. K.; Hollingsworth, J. A.; Jin, M. H.-C.; Harris, J. D.; Duraj, S. A.; Smith, M.; Scheiman, D.; Bohannan, E. W.; Switzer, J. A.; Buhro, W. E.

2002-01-01

The development of thin-film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power (W/kg). Thin-film fabrication studies demonstrate that ternary single source precursors (SSP's) can be used in either a hot or cold-wall spray chemical vapour deposition (CVD) reactor, for depositing CuInS2, CuGaS2, and CuGaInS2 at reduced temperatures (400 to 450 C), which display good electrical and optical properties suitable for photovoltaic (PV) devices. X-ray diffraction studies, energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) confirmed the formation of the single phase CIS, CGS, CIGS thin-films on various substrates at reduced temperatures.

Pt-decorated GaN nanowires with significant improvement in H2 gas-sensing performance at room temperature.

Science.gov (United States)

Abdullah, Q N; Yam, F K; Hassan, Z; Bououdina, M

2015-12-15

Superior sensitivity towards H2 gas was successfully achieved with Pt-decorated GaN nanowires (NWs) gas sensor. GaN NWs were fabricated via chemical vapor deposition (CVD) route. Morphology (field emission scanning electron microscopy and transmission electron microscopy) and crystal structure (high resolution X-ray diffraction) characterizations of the as-synthesized nanostructures demonstrated the formation of GaN NWs having a wurtzite structure, zigzaged shape and an average diameter of 30-166nm. The Pt-decorated GaN NWs sensor shows a high response of 250-2650% upon exposure to H2 gas concentration from 7 to 1000ppm respectively at room temperature (RT), and then increases to about 650-4100% when increasing the operating temperature up to 75°C. The gas-sensing measurements indicated that the Pt-decorated GaN NWs based sensor exhibited efficient detection of H2 at low concentration with excellent sensitivity, repeatability, and free hysteresis phenomena over a period of time of 100min. The large surface-to-volume ratio of GaN NWs and the catalytic activity of Pt metal are the most influential factors leading to the enhancement of H2 gas-sensing performances through the improvement of the interaction between the target molecules (H2) and the sensing NWs surface. The attractive low-cost, low power consumption and high-performance of the resultant decorated GaN NWs gas sensor assure their uppermost potential for H2 gas sensor working at low operating temperature. Copyright © 2015 Elsevier Inc. All rights reserved.

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

International Nuclear Information System (INIS)

Zhang Min; Shi Jun-Jie

2014-01-01

The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μ B among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Electrocatalysts with platinum, cobalt and nickel preparations by mechanical alloyed and CVD for the reaction of oxygen reduction; Electrocatalizadores a base de platino, cobalto y niquel preparados por aleado mecanico y CVD para la reaccion de reduccion de oxigeno

Energy Technology Data Exchange (ETDEWEB)

Garcia C, M A [ININ, 52750 La Marquesa, Estado de Mexico (Mexico)

2008-07-01

In this research, the molecular oxygen reduction reaction (ORR) was investigated on electrocatalysts of Co, Ni, Pt and their alloys CoNi, PtCo, PtNi and PtCoNi by using H{sub 2}SO{sub 4} 0.5 and KOH 0.5 M solutions as electrolytes. The electrocatalysts were synthesized by Mechanical Alloying (MA) and Chemical Vapor Deposition (CVD) processes. For MA, metallic powders were processed during 20 h of milling in a high energy SPEX 8000 mill. For CVD, a hot-wall reactor was utilized and Co, Ni and Pt acetilactetonates were used as precursors. Films were deposited at a total pressure of 1 torr and temperatures of 400-450 C. Electrocatalysts were characterized by X-Ray Diffraction (XRD). Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Electrocatalysts prepared by mechanical alloying showed a homogeneously dispersed agglomeration of particles with nano metric size. Electrocatalysts obtained by CVD showed, in some cases, non uniform films, with particles of nano metric size, as well. The electrocatalytic performance was evaluated by using the Rotating Disk Electrode technique (RDE). Electrocatalysts prepared by MA showed higher activity than those obtained by CVD. All electrocatalysts were evaluated in alkaline media. Only electrocatalysts containing Pt were evaluated in acid media, because those materials with Co, Ni and their alloys showed instability in acidic media. Most electrocatalysts followed a mechanism for the ORR producing a certain proportion of H{sub 2}O{sub 2}. All electrocatalysts, exhibited a fair or good electrocatalytic activity in comparison with other similar reported materials. It was found that MA and CVD are appropriate processes to prepare electrocatalysts for the ORR with particles of nano metric size and performing with an acceptable catalytic activity. PtCoNi 70-23-7% by MA and PtCoNi-CVD electrocatalysts showed the highest activity in alkaline media, while in acidic

Exciton emission from bare and hybrid plasmonic GaN nanorods

Science.gov (United States)

Mohammadi, Fatemesadat; Kunert, Gerd; Hommel, Detlef; Ge, Jingxuan; Duscher, Gerd; Schmitzer, Heidrun; Wagner, Hans Peter

We study the exciton emission of hybrid gold nanoparticle/Alq3 (aluminiumquinoline)/wurtzite GaN nanorods. GaN nanorods of 1.5 μm length and 250 nm diameter were grown by plasma assisted MBE. Hybrid GaN nanorods were synthesized by organic molecular beam deposition. Temperature and power dependent time integrated (TI) and time resolved (TR) photoluminescence (PL) measurements were performed on bare and hybrid structures. Bare nanorods show donor (D0,X) and acceptor bound (A0,X) exciton emission at 3.473 eV and at 3.463 eV, respectively. TR-PL trace modeling reveal lifetimes of 240 ps and 1.4 ns for the (D0,X) and (A0,X) transition. 10 nm gold coated GaN nanorods show a significant PL quenching and (D0,X) lifetime shortening which is tentatively attributed to impact ionization of (D0,X) due to hot electron injection from the gold nanoparticles. This is supported by electron energy loss spectroscopy that shows a redshift of a midgap state transition indicating a reduction of a preexisting band-bending at the nanorod surface due to positive charging of the gold nanoparticles. Inserting a nominally 5 nm thick Alq3 spacer between the nanorod and the gold reduces the PL quenching and lifetime shortening. Plasmonic nanorods with a 30 nm thick Alq3 spacer reveal lifetimes which are nearly identical to uncoated GaN nanorods.

Role of the ganSPQAB Operon in Degradation of Galactan by Bacillus subtilis.

Science.gov (United States)

Watzlawick, Hildegard; Morabbi Heravi, Kambiz; Altenbuchner, Josef

2016-10-15

Bacillus subtilis possesses different enzymes for the utilization of plant cell wall polysaccharides. This includes a gene cluster containing galactan degradation genes (ganA and ganB), two transporter component genes (ganQ and ganP), and the sugar-binding lipoprotein-encoding gene ganS (previously known as cycB). These genes form an operon that is regulated by GanR. The degradation of galactan by B. subtilis begins with the activity of extracellular GanB. GanB is an endo-β-1,4-galactanase and is a member of glycoside hydrolase (GH) family 53. This enzyme was active on high-molecular-weight arabinose-free galactan and mainly produced galactotetraose as well as galactotriose and galactobiose. These galacto-oligosaccharides may enter the cell via the GanQP transmembrane proteins of the galactan ABC transporter. The specificity of the galactan ABC transporter depends on the sugar-binding lipoprotein, GanS. Purified GanS was shown to bind galactotetraose and galactotriose using thermal shift assay. The energy for this transport is provided by MsmX, an ATP-binding protein. The transported galacto-oligosaccharides are further degraded by GanA. GanA is a β-galactosidase that belongs to GH family 42. The GanA enzyme was able to hydrolyze short-chain β-1,4-galacto-oligosaccharides as well as synthetic β-galactopyranosides into galactose. Thermal shift assay as well as electrophoretic mobility shift assay demonstrated that galactobiose is the inducer of the galactan operon regulated by GanR. DNase I footprinting revealed that the GanR protein binds to an operator overlapping the -35 box of the σ(A)-type promoter of Pgan, which is located upstream of ganS IMPORTANCE: Bacillus subtilis is a Gram-positive soil bacterium that utilizes different types of carbohydrates, such as pectin, as carbon sources. So far, most of the pectin degradation systems and enzymes have been thoroughly studied in B. subtilis Nevertheless, the B. subtilis utilization system of galactan, which is

Electrocatalysts with platinum, cobalt and nickel preparations by mechanical alloyed and CVD for the reaction of oxygen reduction

International Nuclear Information System (INIS)

Garcia C, M. A.

2008-01-01

In this research, the molecular oxygen reduction reaction (ORR) was investigated on electrocatalysts of Co, Ni, Pt and their alloys CoNi, PtCo, PtNi and PtCoNi by using H 2 SO 4 0.5 and KOH 0.5 M solutions as electrolytes. The electrocatalysts were synthesized by Mechanical Alloying (MA) and Chemical Vapor Deposition (CVD) processes. For MA, metallic powders were processed during 20 h of milling in a high energy SPEX 8000 mill. For CVD, a hot-wall reactor was utilized and Co, Ni and Pt acetilactetonates were used as precursors. Films were deposited at a total pressure of 1 torr and temperatures of 400-450 C. Electrocatalysts were characterized by X-Ray Diffraction (XRD). Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Electrocatalysts prepared by mechanical alloying showed a homogeneously dispersed agglomeration of particles with nano metric size. Electrocatalysts obtained by CVD showed, in some cases, non uniform films, with particles of nano metric size, as well. The electrocatalytic performance was evaluated by using the Rotating Disk Electrode technique (RDE). Electrocatalysts prepared by MA showed higher activity than those obtained by CVD. All electrocatalysts were evaluated in alkaline media. Only electrocatalysts containing Pt were evaluated in acid media, because those materials with Co, Ni and their alloys showed instability in acidic media. Most electrocatalysts followed a mechanism for the ORR producing a certain proportion of H 2 O 2 . All electrocatalysts, exhibited a fair or good electrocatalytic activity in comparison with other similar reported materials. It was found that MA and CVD are appropriate processes to prepare electrocatalysts for the ORR with particles of nano metric size and performing with an acceptable catalytic activity. PtCoNi 70-23-7% by MA and PtCoNi-CVD electrocatalysts showed the highest activity in alkaline media, while in acidic electrolyte PtCoNi 70

Fabrication of p-type porous GaN on silicon and epitaxial GaN

OpenAIRE

Bilousov, Oleksandr V.; Geaney, Hugh; Carvajal, Joan J.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Giguere, A.; Drouin, D.; Diaz, Francesc; Aguilo, Magdalena; O'Dwyer, Colm

2013-01-01

Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurem...

Lignin monomer composition affects Arabidopsis cell-wall degradability after liquid hot water pretreatment

Directory of Open Access Journals (Sweden)

Ladisch Michael

2010-12-01

Full Text Available Abstract Background Lignin is embedded in the plant cell wall matrix, and impedes the enzymatic saccharification of lignocellulosic feedstocks. To investigate whether enzymatic digestibility of cell wall materials can be improved by altering the relative abundance of the two major lignin monomers, guaiacyl (G and syringyl (S subunits, we compared the degradability of cell wall material from wild-type Arabidopsis thaliana with a mutant line and a genetically modified line, the lignins of which are enriched in G and S subunits, respectively. Results Arabidopsis tissue containing G- and S-rich lignins had the same saccharification performance as the wild type when subjected to enzyme hydrolysis without pretreatment. After a 24-hour incubation period, less than 30% of the total glucan was hydrolyzed. By contrast, when liquid hot water (LHW pretreatment was included before enzyme hydrolysis, the S-lignin-rich tissue gave a much higher glucose yield than either the wild-type or G-lignin-rich tissue. Applying a hot-water washing step after the pretreatment did not lead to a further increase in final glucose yield, but the initial hydrolytic rate was doubled. Conclusions Our analyses using the model plant A. thaliana revealed that lignin composition affects the enzymatic digestibility of LHW pretreated plant material. Pretreatment is more effective in enhancing the saccharification of A. thaliana cell walls that contain S-rich lignin. Increasing lignin S monomer content through genetic engineering may be a promising approach to increase the efficiency and reduce the cost of biomass to biofuel conversion.

Thermoluminescence properties of undoped diamond films deposited using HF CVD technique

Directory of Open Access Journals (Sweden)

Paprocki K.

2018-03-01

Full Text Available Natural diamond has been considered as a perspective material for clinical radiation dosimetry due to its tissuebiocompatibility and chemical inertness. However, the use of natural diamond in radiation dosimetry has been halted by the high market price. The recent progress in the development of CVD techniques for diamond synthesis, offering the capability of growing high quality diamond layers, has renewed the interest in using this material in radiation dosimeters having small geometricalsizes. Polycrystalline CVD diamond films have been proposed as detectors and dosimeters of β and α radiation with prospective applications in high-energy photon dosimetry. In this work, we present a study on the TL properties of undoped diamond film samples grown by the hot filament CVD (HF CVD method and exposed to β and α radiation. The glow curves for both types of radiation show similar character and can be decomposed into three components. The dominant TL peaks are centered at around 610 K and exhibit activation energy of the order of 0.90 eV.

Fabrication and optical characterization of GaN waveguides on (−201)-oriented β-Ga_2O_3

KAUST Repository

Awan, Kashif M.; Muhammad, Mufasila M.; Sivan, Madhavi; Bonca, Spencer; Roqan, Iman S.; Dolgaleva, Ksenia

2017-01-01

Gallium nitride (GaN), a wide-bandgap III-V semiconductor material with a bandgap wavelength λ = 366 nm (for Wurtzite GaN) and transparency window covering the visible spectrum, has a large number of applications for photonics and optoelectronics. However, the optical quality of this material suffers from growth imperfections due to the lack of a suitable substrate. Recent studies have shown that GaN grown on (-201) β - GaO (gallium oxide) has better lattice matching and hence superior optical quality as compared to GaN grown traditionally on AlO (sapphire). In this work, we report on the fabrication of GaN waveguides on GaO substrate, followed by a wet-etch process aimed at the reduction of waveguide surface roughness and improvement of side-wall verticality in these waveguides. The propagation loss in the resulting waveguides has been experimentally determined to be 7.5 dB/cm.

Fabrication and optical characterization of GaN waveguides on (−201)-oriented β-Ga_2O_3

KAUST Repository

Awan, Kashif M.

2017-12-19

Gallium nitride (GaN), a wide-bandgap III-V semiconductor material with a bandgap wavelength λ = 366 nm (for Wurtzite GaN) and transparency window covering the visible spectrum, has a large number of applications for photonics and optoelectronics. However, the optical quality of this material suffers from growth imperfections due to the lack of a suitable substrate. Recent studies have shown that GaN grown on (-201) β - GaO (gallium oxide) has better lattice matching and hence superior optical quality as compared to GaN grown traditionally on AlO (sapphire). In this work, we report on the fabrication of GaN waveguides on GaO substrate, followed by a wet-etch process aimed at the reduction of waveguide surface roughness and improvement of side-wall verticality in these waveguides. The propagation loss in the resulting waveguides has been experimentally determined to be 7.5 dB/cm.

Nanowires and nanotubes of BN, GaN and Si3N4

International Nuclear Information System (INIS)

Deepak, F.L.; Gundiah, G.; Govindaraj, A.; Rao, C.N.

2002-01-01

Simple methods of synthesizing nanotubes and nanowires of boron nitride, gallium nitride and silicon nitride have been investigated. The nanotubes and nanowires have been examined by electron microscopy and other techniques. In the case of BN, activated carbon or multi-walled carbon nanotubes (MWNTs) was heated with boric acid in the presence of NH 3 . With activated carbon, BN nanowires constitute the primary products, but good yields of BN nanotubes are obtained with MWNTs. Aligned BN nanotubes are obtained when aligned MWNTs are employed as the starting material suggesting templating role of carbon nanotubes. Single crystal gallium nitride nanowires have been obtained by heating carbon nanotubes coated with gallium acetylacetonate in NH 3 vapor at 910 o C. Single walled carbon nanotubes were used as templated to reduce the diameter of the GaN nanowires. The growth direction of the GaN nanowires is nearly perpendicular to the [100] planes and the nanowires exhibit satisfactory photoluminescence spectra. Si 3 N 4 nanowires have been synthesized by heating multi-walled carbon nanotubes with silica gel at 1360 o C in an atmosphere of NH 3 . Si 3 N 4 nanotubes are found occasionally when aligned multi-walled nanotubes are employed as templates. (author)

Fabrication and characterization of GaN-based light-emitting diodes without pre-activation of p-type GaN.

Science.gov (United States)

Hu, Xiao-Long; Wang, Hong; Zhang, Xi-Chun

2015-01-01

We fabricated GaN-based light-emitting diodes (LEDs) without pre-activation of p-type GaN. During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN. The electrical measurements showed that the LEDs were featured by a lower forward voltage and higher wall-plug efficiency in comparison with LEDs using pre-activation of p-type GaN. We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient. Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

International Nuclear Information System (INIS)

Lee, Sung-Nam; Paek, H.S.; Son, J.K.; Sakong, T.; Yoon, E.; Nam, O.H.; Park, Y.

2006-01-01

We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

High-efficiency supercapacitor electrodes of CVD-grown graphenes hybridized with multiwalled carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Kalam, Amir Abul; Bae, Joon Ho [Dept. of Nano-physics, Gachon University, Seongnam (Korea, Republic of); Park, Soo Bin; Seo, Yong Ho [Nanotechnology and Advanced Material Engineering, HMC, and GRI, Sejong University, Seoul (Korea, Republic of)

2015-08-15

We demonstrate, for the first time, high-efficiency supercapacitors by utilizing chemical vapor deposition (CVD)-grown graphenes hybridized with multiwalled carbon nanotubes (CNTs). A single-layer graphene was grown by simple CVD growth method, and transferred to polyethylene terephthalate substrates. The bare graphenes were further hybridized with multiwalled CNTs by drop-coating CNTs on graphenes. The supercapacitors using bare graphenes and graphenes with CNTs revealed that graphenes with CNTs resulted in enhanced supercapacitor performances of 2.2- (the mass-specific capacitance) and 4.4-fold (the area-specific capacitance) of those of bare graphenes. Our strategy to improve electrochemical performance of CVD-grown graphenes is advantageous for large-scale graphene electrodes due to high electrical conductivity of CVD-grown graphenes and cost-effectiveness of using multiwalled CNTs as compared to conventional employment of single-walled CNTs.

High-efficiency supercapacitor electrodes of CVD-grown graphenes hybridized with multiwalled carbon nanotubes

International Nuclear Information System (INIS)

Kalam, Amir Abul; Bae, Joon Ho; Park, Soo Bin; Seo, Yong Ho

2015-01-01

We demonstrate, for the first time, high-efficiency supercapacitors by utilizing chemical vapor deposition (CVD)-grown graphenes hybridized with multiwalled carbon nanotubes (CNTs). A single-layer graphene was grown by simple CVD growth method, and transferred to polyethylene terephthalate substrates. The bare graphenes were further hybridized with multiwalled CNTs by drop-coating CNTs on graphenes. The supercapacitors using bare graphenes and graphenes with CNTs revealed that graphenes with CNTs resulted in enhanced supercapacitor performances of 2.2- (the mass-specific capacitance) and 4.4-fold (the area-specific capacitance) of those of bare graphenes. Our strategy to improve electrochemical performance of CVD-grown graphenes is advantageous for large-scale graphene electrodes due to high electrical conductivity of CVD-grown graphenes and cost-effectiveness of using multiwalled CNTs as compared to conventional employment of single-walled CNTs

Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

Science.gov (United States)

Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

2017-01-01

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

Structure guided GANs

Science.gov (United States)

Cao, Feidao; Zhao, Huaici; Liu, Pengfei

2017-11-01

Generative adversarial networks (GANs) has achieved success in many fields. However, there are some samples generated by many GAN-based works, whose structure is ambiguous. In this work, we propose Structure Guided GANs that introduce structural similar into GANs to overcome the problem. In order to achieve our goal, we introduce an encoder and a decoder into a generator to design a new generator and take real samples as part of the input of a generator. And we modify the loss function of the generator accordingly. By comparison with WGAN, experimental results show that our proposed method overcomes largely sample structure ambiguous and can generate higher quality samples.

Electronic structures and optical properties of GaN nanotubes with MgGa–ON co-doping

International Nuclear Information System (INIS)

Yang, Mao; Shi, Jun-jie; Zhang, Min; Zhang, Shuai; Bao, Zhi-qiang; Luo, Shao-jun; Zhou, Tie-Cheng; Zhu, Tian-cong; Li, Xiang; Li, Jia

2013-01-01

Both the electronic structures and the optical properties of single-walled zigzag GaN nanotubes (NTs) with Mg Ga –O N co-doping are investigated using first-principles calculations. We find that the Mg Ga –O N defect complex can exist stably in GaN NTs. The direct band gap width of the GaN NTs can be reduced by means of the Mg Ga –O N co-doping. The electrons of the valence band maximum (VBM) state are localized around the N atoms bonded with the Mg atom. The imaginary part ε 2 of the complex dielectric function of GaN NTs with Mg Ga –O N co-doping has a sharp peak closely related to the optical transitions between the VBM and conduction band minimum states. - Highlights: ► The Mg Ga –O N defect complex can exist stably in GaN NTs. ► The band gap of the GaN NTs can be reduced due to the Mg Ga –O N co-doping. ► The VBM states are localized around the N atoms bonded with the Mg atom. ► The ε 2 -plot has a peak related to the optical transition from the VBM to CBM state

Investigation of GaN LED with Be-implanted Mg-doped GaN layer

International Nuclear Information System (INIS)

Huang, H.-W.; Kao, C.C.; Chu, J.T.; Kuo, H.C.; Wang, S.C.; Yu, C.C.; Lin, C.F.

2004-01-01

We report the electrical and optical characteristics of GaN light emitting diode (LED) with beryllium (Be) implanted Mg-doped GaN layer. The p-type layer of Be-implanted GaN LED showed a higher hole carrier concentration of 2.3 x 10 18 cm -3 and low specific contact resistance value of 2.0 x 10 -4 Ωcm 2 than as-grown p-GaN LED samples without Be-implantation. The Be-implanted GaN LEDs with InGaN/GaN MQW show slightly lower light output (about 10%) than the as-grown GaN LEDs, caused by the high RTA temperature annealing process

Friction Properties of Polished Cvd Diamond Films Sliding against Different Metals

Science.gov (United States)

Lin, Zichao; Sun, Fanghong; Shen, Bin

2016-11-01

Owing to their excellent mechanical and tribological properties, like the well-known extreme hardness, low coefficient of friction and high chemical inertness, chemical vapor deposition (CVD) diamond films have found applications as a hard coating for drawing dies. The surface roughness of the diamond films is one of the most important attributes to the drawing dies. In this paper, the effects of different surface roughnesses on the friction properties of diamond films have been experimentally studied. Diamond films were fabricated using hot filament CVD. The WC-Co (Co 6wt.%) drawing dies were used as substrates. A gas mixture of acetone and hydrogen gas was used as the feedstock gas. The CVD diamond films were polished using mechanical polishing. Polished diamond films with three different surface roughnesses, as well as the unpolished diamond film, were fabricated in order to study the tribological performance between the CVD diamond films and different metals with oil lubrication. The unpolished and polished CVD diamond films are characterized with scanning electron microscope (SEM), atomic force microscope (AFM), surface profilometer, Raman spectrum and X-ray diffraction (XRD). The friction examinations were carried out by using a ball-on-plate type reciprocating friction tester. Low carbide steel, stainless steel, copper and aluminum materials were used as counterpart balls. Based on this study, the results presented the friction coefficients between the polished CVD films and different metals. The friction tests demonstrate that the smooth surface finish of CVD diamond films is beneficial for reducing their friction coefficients. The diamond films exhibit low friction coefficients when slid against the stainless steel balls and low carbide steel ball, lower than that slid against copper ball and aluminum ball, attributed to the higher ductility of copper and aluminum causing larger amount of wear debris adhering to the sliding interface and higher adhesive

Systematic study on synthesis and purification of double-walled carbon nanotubes synthesized via CVD

Science.gov (United States)

Jedrzejewska, A.; Kalenczuk, R. J.; Mijowska, E.

2011-12-01

Carbon nanotubes have unique properties, such as thermal and electrical conductance, which could be useful in the fields of aerospace, microelectronics and biotechnology. However, these properties may vary widely depending on the dimensions, uniformity and purity of the nanotube. Nanotube samples typically contain a significant percentage of more allotropes forms of carbon as well as metal particles left over from catalysts used in manufacturing. Purity characterization of double-walled carbon nanotubes (DWCNTs) is an increasingly popular topic in the field of carbon nanotechnology. In this study, DWCNTs were synthesized in a catalytic reaction, using Fe:MgO as catalyst and methane or methane/ethanol as carbon feedstock for chemical vapor deposition (CVD). The addition of ethanol as carbon feedstock allowed to investigate the influence of oxygen on the sample quality. The purification of the as-produced material from the metallic particles and the catalyst support was performed by sonication in an acid solution. The influence of the duration of the acid treatment using ultrasound on the sample purity was investigated, and the optimal value of this parameter was found. Transmission electron microscopy (TEM) images confirmed the removal of impurities and served to elucidate the morphology of the samples. The purity of carbon nanotubes was analyzed using thermal gravimetric analysis (TGA). The Raman spectra of the samples, as a measure of the concentration of defects, were also reported.

Interactions between wall rocks around magma and hot water. Magma shuhen no hekigan/nessui sogo sayo

Energy Technology Data Exchange (ETDEWEB)

Fujimoto, K.

1992-12-01

This paper describes interactions between wall rocks around magma and hot water. The paper discusses effects of hydrothermal environments on dynamic properties of rock minerals with respect to hydrolytic weakening (decrease in dynamic strength of a mineral under presence of water) and reaction enhanced deformation (deformation accelerated by chemical change occurring in a mineral itself). It also explains chemical reactivity of minerals under hydrothermal enviroments with respect to four types of chemical changes in minerals, factors governing mineral dissolution rates, and importance of equilibrium and non-equilibrium in main components in reactions between minerals and waters. These statements quote mainly results of indoor experiments. The paper indicates the following matters as problems to be discussed on interactions between wall rocks around intrusive rocks and hot waters: Deviation from chemical equilibrium in reactions between rocks and waters; change in permeability as a result of reactions between rocks and waters; and possibilities of hydrolytic weakening in rocks around intrusive rock bodies. 52 refs., 6 figs.

Impact ionization of excitons in electric field of GaN and quantum wells of GaN/AlGaN

International Nuclear Information System (INIS)

Nel'son, D.K.; Yakobson, M.A.; Kagan, V.D.; Gil, B.; Grandjean, N.; Beaumont, B.; Massier, J.; Gibart, P.

2001-01-01

The effect of the exciton states impact ionization in the GaN exploit films and in the GaN/AlGaN structures with quantum wells is studied. The study was carried out through the optical method, based on the exciton photoluminescence quenching by applying the electric field. It is established that in the process of the electrons relaxation by energy and pulse the scattering on the admixtures prevails over the scattering on the acoustic phonons. The average length of the hot electrons free run is evaluated. The average length of the hot electrons free run in the GaN/AlGaN wells proved to be by the value order higher than in the GaN epitaxial films, which is conditioned by decrease in the probability of the electrons scattering in the two-dimensional case [ru

Self-organization of dislocation-free, high-density, vertically aligned GaN nanocolumns involving InGaN quantum wells on graphene/SiO2 covered with a thin AlN buffer layer

International Nuclear Information System (INIS)

Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

2016-01-01

We demonstrated the self-organization of high-density GaN nanocolumns on multilayer graphene (MLG)/SiO 2 covered with a thin AlN buffer layer by RF-plasma-assisted molecular beam epitaxy. MLG/SiO 2 substrates were prepared by the transfer of CVD graphene onto thermally oxidized SiO 2 /Si [100] substrates. Employing the MLG with an AlN buffer layer enabled the self-organization of high-density and vertically aligned nanocolumns. Transmission electron microscopy observation revealed that no threading dislocations, stacking faults, or twinning defects were included in the self-organized nanocolumns. The photoluminescence (PL) peak intensities of the self-organized GaN nanocolumns were 2.0–2.6 times higher than those of a GaN substrate grown by hydride vapor phase epitaxy. Moreover, no yellow luminescence or ZB-phase GaN emission was observed from the nanocolumns. An InGaN/GaN MQW and p-type GaN were integrated into GaN nanocolumns grown on MLG, displaying a single-peak PL emission at a wavelength of 533 nm. Thus, high-density nitride p–i–n nanocolumns were fabricated on SiO 2 /Si using the transferred MLG interlayer, indicating the possibility of developing visible nanocolumn LEDs on graphene/SiO 2 . (paper)

Taevo Gans / Ene Ammer

Index Scriptorium Estoniae

Ammer, Ene

1998-01-01

Sisearhitekt Taevo Gansist. Tudengipõlvest, selle aja projektidest, sõpruskonnast, tandemist Summatavet & Gans, Venemaa tellimustest, kaastöölistest. Üksinda Hommilkumaal vene tarbekunsti näitusega 1974. a. 1988. a. loodud perefirmast "GaDis" (omanikud Taevo, Helle Gans, Riia Oja), mis nõustab ka "Wermot" mööbli osas. "GaDise" sisekujundusprojektidest, millega Taevo ja Helle Gans tegelevad üheskoos

Nitrogen and hydrogen related infrared absorption in CVD diamond films

Energy Technology Data Exchange (ETDEWEB)

Titus, E. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal)]. E-mail: elby@mec.ua.pt; Ali, N. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal); Cabral, G. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal); Madaleno, J.C. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal); Neto, V.F. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal); Gracio, J. [Department of Mechanical Engineering, University of Aveiro, 3810-193 (Portugal); Ramesh Babu, P [Materials Ireland, Polymer research Centre, School of Physics, Dublin (Ireland); Sikder, A.K. [Department of Physics, Indian Institute of Technology (IIT), Bombay (India); Okpalugo, T.I. [Northern Ireland Bio-Engineering Centre, NIBEC, University of Ulster (United Kingdom); Misra, D.S. [Department of Physics, Indian Institute of Technology (IIT), Bombay (India)

2006-09-25

In this paper, we investigate on the presence of hydrogen and nitrogen related infrared absorptions in chemical vapour deposited (CVD) diamond films. Investigations were carried out in cross sections of diamond windows, deposited using hot filament CVD (HFCVD). The results of Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopy carried out in a cross section of self-standing diamond sheets are presented. The FTIR spectra showed several features that have not been reported before. In order to confirm the frequency of nitrogen related vibrations, ab-initio calculations were carried out using GAMESS program. The investigations showed the presence of several C-N related peaks in one-phonon (1000-1333 cm{sup -1}). The deconvolution of the spectra in the three-phonon region (2700-3150 cm{sup -1}) also showed a number of vibration modes corresponding to sp {sup m}CH {sub n} phase of carbon. Elastic recoil detection analysis (ERDA) was employed to compare the H content measured using FTIR technique. Using these measurements we point out that the oscillator strength of the different IR modes varies depending upon the structure and H content of CVD diamond sheets.

In situ synthesis and characterization of GaN nanorods through thermal decomposition of pre-grown GaN films

International Nuclear Information System (INIS)

Yan, P; Qin, D; An, Y K; Li, G Z; Xing, J; Liu, J J

2008-01-01

Herein we describe a thermal treatment route to synthesize gallium nitride (GaN) nanorods. In this method, GaN nanorods were synthesized by thermal treatment of GaN films at a temperature of 800 deg. C. The morphology and structure of GaN nanorods were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that GaN nanorods have a hexagonal wurtzite structure with diameters ranging from 30 to 50 nm. Additionally, GaN nanoplates are also founded in the products. The growth process of GaN nanostructures was investigated and a thermal decomposition mechanism was proposed. Our method provides a cost-effective route to fabricate GaN nanorods, which will benefit the fabrication of one-dimensional nanomaterials and device applications

Light effect in photoionization of traps in GaN MESFETs

Directory of Open Access Journals (Sweden)

H. Arabshahi

2009-09-01

Full Text Available Trapping of hot electron behavior by trap centers located in buffer layer of a wurtzite phase GaN MESFET has been simulated using an ensemble Monte Carlo simulation. The results of the simulation show that the trap centers are responsible for current collapse in GaN MESFET at low temperatures. These electrical traps degrade the performance of the device at low temperature. On the opposite, a light-induced increase in the trap-limited drain current, results from the photoionization of trapped carriers and their return to the channel under the influence of the built in electric field associated with the trapped charge distribution. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted drain current and other electrical characteristics for the simulated device including trapping center effects show close agreement with the available experimental data.

Impact of GaN transition layers in the growth of GaN epitaxial layer on silicon

International Nuclear Information System (INIS)

Zhao Danmei; Zhao Degang; Jiang Desheng; Liu Zongshun; Zhu Jianjun; Chen Ping; Liu Wei; Li Xiang; Shi Ming

2015-01-01

A method for growing GaN epitaxial layer on Si (111) substrate is investigated. Due to the large lattice mismatch between GaN and AlN, GaN grown directly above an AlN buffer layer on the Si substrate turns out to be of poor quality. In this study, a GaN transition layer is grown additionally on the AlN buffer before the GaN epitaxial growth. By changing the growth conditions of the GaN transition layer, we can control the growth and merging of islands and control the transfer time from 3D to 2D growth mode. With this method, the crystalline quality of the GaN epitaxial layer can be improved and the crack density is reduced. Here, we have investigated the impact of a transition layer on the crystalline quality and stress evolution of a GaN epitaxial layer with methods of X-ray diffraction, optical microscopy and in situ reflectivity trace. With the increasing thickness of transition layer, the crack decreases and the crystalline quality is improved. But when the transition layer exceeds a critical thickness, the crystalline quality of the epilayer becomes lower and the crack density increases. (paper)

Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

Energy Technology Data Exchange (ETDEWEB)

Choudhary, B. S. [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India); Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Singh, A.; Tyagi, P. K. [Department of Applied Physics, Delhi Technological University, Delhi 110042 (India); Tanwar, S. [Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Kumar, M. Senthil; Kushvaha, S. S., E-mail: kushvahas@nplindia.org [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India)

2016-04-13

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

Construction of concrete hot cells; requirements for shielding windows for concrete walls with different densities

International Nuclear Information System (INIS)

1987-10-01

The shielding windows form part of the basic equipment of hot cells for remote handling, as defined in standard DIN 25 420 part 1. The draft standard in hand is intended to specify the design and manufacture requirements, especially with regard to main dimensions, sight quality, shielding effects, and radiation resistance. The standard refers to three types of shielding window with surface area design (product of density and wall thickness) corresponding to concrete walls of the densities 2.4, 3.4, and 4.0 g/cm 3 . The windows fit to three types of concrete of common usage, and the design is made for Co-60 radiation, with attenuation factors of about 10 4 , 10 6 , or 10 7 . For concrete walls with densities between these data, a shielding window suitable to the next higher density data is to be chosen. (orig./HP) [de

Z L GAN

Indian Academy of Sciences (India)

Z L GAN. Articles written in Sadhana. Volume 43 Issue 4 April 2018 pp 59. Effect of scale size, orientation type and dispensing method on void formation in the CUF encapsulation of BGA · AIZAT ABAS FEI CHONG NG Z L GAN M H H ISHAK M Z ABDULLAH GEAN YUEN CHONG · More Details Abstract Fulltext PDF.

CVD - main concepts, applications and restrictions

International Nuclear Information System (INIS)

Bliznakovska, B.; Milosevski, M.; Krawczynski, S.; Meixner, C.; Koetter, H.R.

1993-01-01

Despite of the fact that the existing literature covering the last two decades is plentiful with data related to CVD, this document is an attempt to provide to a reader a concise information about the nature of CVD technique at production of technologically important materials as well as to point at special references. The text is devided into three separate sections. The first section, The Main Features of CVD, is intended to give a complete comprehensive picture of the CVD technique through process description and characterization. The basic principles of thermodynamics, CVD chemical reactions classification, CVD chemical kinetics aspects and physics of CVD (with particular attention on the gas-flow phenomena) are included. As an additional aspect, in CVD unavoidable aspect however, the role of the coating/substrate compatibility on the overall process was outlined. The second section, CVD Equipment, concerns on the pecularities of the complete CVD unit pointing out the individual significances of the separate parts, i.e. pumping system, reactor chamber, control system. The aim of this section is to create to a reader a basic understanding of the arising problems but connected to be actual CVD performance. As a final goal of this review the reader's attention is turned upon the CVD applications for production of an up-to-date important class of coatings such as multilayer coatings. (orig.)

Hot-wire chemical vapour deposition of carbon nanotubes

CSIR Research Space (South Africa)

Cummings, FR

2006-07-01

Full Text Available ablation of graphite, carbon-arc discharge and chemical vapour deposition (CVD). However, some of these techniques have been shown to be expensive due to high deposition temperatures and are not easily controllable. Recently hot-wire chemical vapour...

Improved InGaN/GaN quantum wells on treated GaN template with a Ga-rich GaN interlayer

International Nuclear Information System (INIS)

Fang, Zhilai; Shen, Xiyang; Wu, Zhengyuan; Zhang, Tong-Yi

2015-01-01

Treated GaN template was achieved by in situ droplet epitaxy of a Ga-rich GaN interlayer on the conventional GaN template. InGaN/GaN quantum wells (QWs) were grown on the conventional and treated GaN templates under the same growth conditions and then comprehensively characterized. The indium homogeneity in the InGaN layers and the interface sharpness between InGaN and GaN layers of the InGaN/GaN QWs on the treated GaN template were significantly improved. The emission intensity from the InGaN/GaN QWs on the treated GaN template was enhanced by 20% than that on the conventional GaN template, which was attributed to the strain reduction and the improvement in crystalline quality. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

P-type doping of GaN

International Nuclear Information System (INIS)

Wong, R.K.

2000-01-01

After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover

P-type doping of GaN

Energy Technology Data Exchange (ETDEWEB)

Wong, Raechelle Kimberly [Univ. of California, Berkeley, CA (United States)

2000-04-01

After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover.

Investigation of different mechanisms of GaN growth induced on AlN and GaN nucleation layers

International Nuclear Information System (INIS)

Tasco, V.; Campa, A.; Tarantini, I.; Passaseo, A.; Gonzalez-Posada, F.; Munoz, E.; Redondo-Cubero, A.; Lorenz, K.; Franco, N.

2009-01-01

The evolution of GaN growth on AlN and GaN nucleation layers is compared through morphological and structural analyses, including ion beam analysis. By using AlN nucleation layer grown at high temperature, improved crystalline quality is exhibited by 300 nm thin GaN epilayers. GaN (002) x-ray rocking curve as narrow as 168 arc sec and atomic-step surface morphology characterize such a thin GaN film on AlN. Defects are strongly confined into the first 50 nm of growth, whereas a fast laterally coherent growth is observed when increasing thickness, as an effect of high temperature AlN surface morphology and Ga adatom dynamics over this template

Synthetic Strategies and Applications of GaN Nanowires

Directory of Open Access Journals (Sweden)

Guoquan Suo

2014-01-01

Full Text Available GaN is an important III-V semiconductor material with a direct band gap of 3.4 eV at 300 K. The wide direct band gap makes GaN an attractive material for various applications. GaN nanowires have demonstrated significant potential as fundamental building blocks for nanoelectronic and nanophotonic devices and also offer substantial promise for integrated nanosystems. In this paper, we provide a comprehensive review on the general synthetic strategies, characterizations, and applications of GaN nanowires. We first summarize several growth techniques of GaN nanowires. Subsequently, we discuss mechanisms involved to generate GaN nanowires from different synthetic schemes and conditions. Then we review some characterization methods of GaN nanowires. Finally, several kinds of main applications of GaN nanowires are discussed.

A DFT study on NEA GaN photocathode with an ultrathin n-type Si-doped GaN cap layer

Science.gov (United States)

Xia, Sihao; Liu, Lei; Kong, Yike; Diao, Yu

2016-10-01

Due to the drawbacks of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, a new-type NEA GaN photocathodes with heterojunction surface dispense with Cs activation are proposed. This structure can be obtained through the coverage of an ultrathin n-type Si-doped GaN cap layer on the p-type Mg-doped GaN emission layer. The influences of the cap layer on the photocathode are calculated using DFT. This study indicates that the n-type cap layer can promote the photoemission characteristics of GaN photocathode and demonstrates the probability of the preparation of a NEA GaN photocathode with an n-type cap layer.

Effect of the spatial filtering and alignment error of hot-wire probes in a wall-bounded turbulent flow

International Nuclear Information System (INIS)

Segalini, A; Cimarelli, A; Rüedi, J-D; De Angelis, E; Talamelli, A

2011-01-01

The effort to describe velocity fluctuation distributions in wall-bounded turbulent flows has raised different questions concerning the accuracy of hot-wire measurement techniques close to the wall and more specifically the effect of spatial averaging resulting from the finite size of the wire. Here, an analytical model which describes the effect of the spatial filtering and misalignment of hot-wire probes on the main statistical moments in turbulent wall-bounded flows is presented. The model, which is based on the two-point velocity correlation function, shows that the filtering is directly related to the transverse Taylor micro-scale. By means of turbulent channel flow DNS data, the capacity of the model to accurately describe the probe response is established. At the same time, the filtering effect is appraised for different wire lengths and for a range of misalignment angles which can be expected from good experimental practice. Effects of the second-order terms in the model equations are also taken into account and discussed. In order to use the model in a practical situation, the Taylor micro-scale distribution at least should be provided. A simple scaling law based on classic turbulence theory is therefore introduced and finally employed to estimate the filtering effect for different wire lengths

First wall and shield components manufacturing by hot isostatic pressing

International Nuclear Information System (INIS)

Lind, Anders; Tegman, R.

1994-01-01

At a meeting in Garching in June 1994 Hot Isostatic Pressing (HIP) was presented as a possible route to manufacture ITER first wall and shield components. The main advantages of the HIP concept include excellent and uniform mechanical properties of the produced materials and joints, high reliability and robustness of the HIP process, double containment of coolant, good flexibility concerning general design as well as size and location for inner cooling tubes, low cost and short delivery times, and a good near net shape capability for components in size up to 15 tons. To assess the applicability of HIP for the manufacturing of ITER first wall and shield components, it was agreed * to choose possible production parameters based in the present know-how, * to produce a compound mock-up in one shot from available solid steel/powder copper/steel tubes to demonstrate the joinability of the materials, * to examine the produced mock-up/materials by multi array ultrasonic testing, limited mechanical testing, metallography, scanning electron microscopy and energy dispersive spectroscopy, and * to compile data on Type 316L steels produced by HIP. Preliminary results and the mock-up were presented at a meeting in Garching in mid July 1994. This study clearly shows the excellent joinability of a copper alloy (Cu-0.5%Zr) and stainless steels (Type 304, 316 L) by HIP at temperatures close to the melting temperature of copper, with only limited influence on the microstructures, which makes it possible to HIP the first wall and shield structure in one step. Excellent mechanical properties of the compound are obtained with the copper alloy and not the joint being the weakest part. 7 refs, 21 figs, 1 tab

Influence of Coherent Structures on the Wall Shear Stress in Axial Flow Between a Cylinder and a Plane Wall

International Nuclear Information System (INIS)

Khabbouchi, Imed; Guellouz, Mohamed Sadok; Tavoularis, Stavros

2009-01-01

Synchronised hot-film and hot-wire measurements were made in the narrower region of a rectangular channel containing a cylindrical rod. The hot-film probe was mounted flush with the channel bottom wall to measure the wall shear stress, while the hot-wire probe was placed at a fixed position, selected in order to easily detect the passage of coherent structures. Mean and rms profiles of the wall shear stress show the influence of the gap to diameter ratio on their respective distributions. The latter presented peculiarities that could only be explained by the presence of coherent structures in the flow between the rod and the wall. Evidence of this presence is seen in the velocity power spectra. The strong influence of the coherent structures on the wall shear stress spatial and temporal distributions is established through velocity-wall shear stress cross-correlations functions and through conditionally sampled measurements

GaN based nanorods for solid state lighting

Energy Technology Data Exchange (ETDEWEB)

Li Shunfeng; Waag, Andreas [Institute of Semiconductor Technology, Braunschweig University of Technology, 38106 Braunschweig (Germany)

2012-04-01

In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

Future prospect of remote Cat-CVD on the basis of the production, transportation and detection of H atoms

International Nuclear Information System (INIS)

Umemoto, Hironobu; Matsumura, Hideki

2008-01-01

The future prospect of remote Cat-CVD, in which the decomposition and the deposition chambers are separated, is discussed on the basis of the absolute density measurements of H atoms. It is now well recognized that uniform deposition is possible on a large area without plasma damages by Cat-CVD. However, we may not overlook the demerits in Cat-CVD. One of the demerits is the poisoning of the catalyzer surfaces by the material gases, both temporary and permanent. One technique to overcome this problem is remote Cat-CVD. The question is how to separate the decomposition and deposition areas. If the separation is not enough, there should be back diffusion of the material gases, which will poison the catalyzers. If the separation is too tight, radicals may not effuse out from the decomposition chamber. These problems are discussed and it is shown that SiO 2 coating to reduce the radical recombination rates on walls is promising. The possibility of the polytetrafluoroethene coating by Cat-CVD is also discussed

High Performance Walls in Hot-Dry Climates

Energy Technology Data Exchange (ETDEWEB)

Hoeschele, Marc [National Renewable Energy Lab. (NREL), Golden, CO (United States); Springer, David [National Renewable Energy Lab. (NREL), Golden, CO (United States); Dakin, Bill [National Renewable Energy Lab. (NREL), Golden, CO (United States); German, Alea [National Renewable Energy Lab. (NREL), Golden, CO (United States)

2015-01-01

High performance walls represent a high priority measure for moving the next generation of new homes to the Zero Net Energy performance level. The primary goal in improving wall thermal performance revolves around increasing the wall framing from 2x4 to 2x6, adding more cavity and exterior rigid insulation, achieving insulation installation criteria meeting ENERGY STAR's thermal bypass checklist, and reducing the amount of wood penetrating the wall cavity.

A novel continuous process for synthesis of carbon nanotubes using iron floating catalyst and MgO particles for CVD of methane in a fluidized bed reactor

Energy Technology Data Exchange (ETDEWEB)

Maghsoodi, Sarah; Khodadadi, Abasali [Catalysis and Nanostructured Materials Research Laboratory, School of Chemical Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Mortazavi, Yadollah, E-mail: mortazav@ut.ac.ir [Nanoelectronics Centre of Excellence, University of Tehran, POB 11365-4563, Tehran (Iran, Islamic Republic of)

2010-02-15

A novel continuous process is used for production of carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CVD) of methane on iron floating catalyst in situ deposited on MgO in a fluidized bed reactor. In the hot zone of the reactor, sublimed ferrocene vapors were contacted with MgO powder fluidized by methane feed to produce Fe/MgO catalyst in situ. An annular tube was used to enhance the ferrocene and MgO contacting efficiency. Multi-wall as well as single-wall CNTs was grown on the Fe/MgO catalyst while falling down the reactor. The CNTs were continuously collected at the bottom of the reactor, only when MgO powder was used. The annular tube enhanced the contacting efficiency and improved both the quality and quantity of CNTs. The SEM and TEM micrographs of the products reveal that the CNTs are mostly entangled bundles with diameters of about 10-20 nm. Raman spectra show that the CNTs have low amount of amorphous/defected carbon with I{sub G}/I{sub D} ratios as high as 10.2 for synthesis at 900 deg. C. The RBM Raman peaks indicate formation of single-walled carbon nanotubes (SWNTs) of 1.0-1.2 nm diameter.

Piezotronic Effect in Polarity-Controlled GaN Nanowires.

Science.gov (United States)

Zhao, Zhenfu; Pu, Xiong; Han, Changbao; Du, Chunhua; Li, Linxuan; Jiang, Chunyan; Hu, Weiguo; Wang, Zhong Lin

2015-08-25

Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

Multifunctional carbon nanotubes with nanoparticles embedded in their walls

International Nuclear Information System (INIS)

Mattia, D; Korneva, G; Sabur, A; Friedman, G; Gogotsi, Y

2007-01-01

Controlled amounts of nanoparticles ranging in size and composition were embedded in the walls of carbon nanotubes during a template-assisted chemical vapour deposition (CVD) process. The encapsulation of gold nanoparticles enabled surface enhanced Raman spectroscopy (SERS) detection of glycine inside the cavity of the nanotubes. Iron oxide particles are partially reduced to metallic iron during the CVD process giving the nanotubes ferromagnetic behaviour. At high nanoparticle concentrations, particle agglomerates can form. These agglomerates or larger particles, which are only partially embedded in the walls of the nanotubes, are covered by additional carbon layers inside the hollow cavity of the tube producing hillocks inside the nanotubes, with sizes comparable to the bore of the tube

GaN Micromechanical Resonators with Meshed Metal Bottom Electrode.

Science.gov (United States)

Ansari, Azadeh; Liu, Che-Yu; Lin, Chien-Chung; Kuo, Hao-Chung; Ku, Pei-Cheng; Rais-Zadeh, Mina

2015-03-17

This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO₂) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient ( d 33 ) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF₂) etch and therefore eliminating the need for backside lithography and etching.

The Formation and Characterization of GaN Hexagonal Pyramids

Science.gov (United States)

Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

2013-05-01

GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

Gan-Hang tectonic belt and its geologic significance

International Nuclear Information System (INIS)

Deng Jiarui; Zhang Zhiping.

1989-01-01

Gan-Hang tectonic belt is predominantly controlled by Gan-Hang fracture zone. It is mainly composed of Yongfeng-Zhuji downwarping zone, Gan-Hang volcanic activity structural belt and Gan-Hang red basin downfaulted zone. Gan-Hang fracture zone is derived from evolution and development of Shaoxing-Jiangshan deep fracture. It is mainly composed of three deep and large fracture and Fuzhou-Yongfeng large fracture. The fracture zone is a long active belt, but in each active period the geologic structural patterns intensity, depth and forming time were not same. Gan-Hang tectonic belt possesses obvious inheritance. It has always maintained the character of the relative depression or low land since the Caledonian movement. This specific structural environment is favourable for uranium mineralization. At any rate, the formation of this uranium minerogenetic zone has been experiencing a long and complicated processes which were closely associated with long activity of Gan-Hang fracture zone

Effect of substrate roughness on growth of diamond by hot filament ...

Indian Academy of Sciences (India)

Administrator

Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate ... toughness of the film as the crystal changes its phase from monocrystalline to .... is a characteristic of graphite. We mark the.

Synthesis of Multi-Walled Carbon Nanotubes from Plastic Waste Using a Stainless-Steel CVD Reactor as Catalyst.

Science.gov (United States)

Tripathi, Pranav K; Durbach, Shane; Coville, Neil J

2017-09-22

The disposal of non-biodegradable plastic waste without further upgrading/downgrading is not environmentally acceptable and many methods to overcome the problem have been proposed. Herein we indicate a simple method to make high-value nanomaterials from plastic waste as a partial solution to the environmental problem. Laboratory-based waste centrifuge tubes made of polypropylene were chosen as a carbon source to show the process principle. In the process, multi-walled carbon nanotubes (MWCNTs) were synthesized from plastic waste in a two-stage stainless steel 316 (SS 316) metal tube that acted as both reactor vessel and catalyst. The steel reactor contains Fe (and Ni, and various alloys), which act as the catalyst for the carbon conversion process. The reaction and products were studied using electron probe microanalysis, thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy and scanning electron microscopy. Optimization studies to determine the effect of different parameters on the process showed that the highest yield and most graphitized MWCNTs were formed at 900 °C under the reaction conditions used (yield 42%; Raman I D / I G ratio = 0.48). The high quality and high yield of the MWCNTs that were produced in a flow reactor from plastic waste using a two stage SS 316 chemical vapor deposition (CVD) furnace did not require the use of an added catalyst.

Synthesis of Multi-Walled Carbon Nanotubes from Plastic Waste Using a Stainless-Steel CVD Reactor as Catalyst

Directory of Open Access Journals (Sweden)

Pranav K. Tripathi

2017-09-01

Full Text Available The disposal of non-biodegradable plastic waste without further upgrading/downgrading is not environmentally acceptable and many methods to overcome the problem have been proposed. Herein we indicate a simple method to make high-value nanomaterials from plastic waste as a partial solution to the environmental problem. Laboratory-based waste centrifuge tubes made of polypropylene were chosen as a carbon source to show the process principle. In the process, multi-walled carbon nanotubes (MWCNTs were synthesized from plastic waste in a two-stage stainless steel 316 (SS 316 metal tube that acted as both reactor vessel and catalyst. The steel reactor contains Fe (and Ni, and various alloys, which act as the catalyst for the carbon conversion process. The reaction and products were studied using electron probe microanalysis, thermogravimetric analysis, Raman spectroscopy and transmission electron microscopy and scanning electron microscopy. Optimization studies to determine the effect of different parameters on the process showed that the highest yield and most graphitized MWCNTs were formed at 900 °C under the reaction conditions used (yield 42%; Raman ID/IG ratio = 0.48. The high quality and high yield of the MWCNTs that were produced in a flow reactor from plastic waste using a two stage SS 316 chemical vapor deposition (CVD furnace did not require the use of an added catalyst.

Experimental study of bypass flow in near wall gaps of a pebble bed reactor using hot wire anemometry technique

International Nuclear Information System (INIS)

Amini, Noushin; Hassan, Yassin A.

2014-01-01

Highlights: • Coolant flow behavior in near wall gaps of a pebble bed reactor is studied. • Hot wire anemometry is applied for high frequency velocity measurements. • Bypass flow is identified within the velocity profiles of near wall gaps. • Effect of gap geometry and Reynolds number on bypass flow is investigated. • Variation of velocity power spectra with radial location and Reynolds number is studied. - Abstract: Coolant flow behavior through the core of an annular pebble bed reactor is investigated in this experimental study. A high frequency hot wire anemometry system coupled with an X-probe is used for measurement of axial and radial velocity components at different points within two near wall gaps at five different modified Reynolds numbers (Re m = 2043–6857). The velocity profiles within the gaps verify the presence of an area of increased velocity close to the pebble bed outer reflector wall, which is known as the bypass flow. Moreover, the characteristics of the coolant flow profile are seen to be highly dependent on the gap geometry. The effect of Reynolds number on the velocity profiles varies as the geometry of the gap changes. The time histories of the local velocities measured with considerably high frequency are further analyzed using power spectral density technique. Power spectral plots illustrate substantial spatial variation of the energy content, spectral shape, and the slope of the energy cascade region. A significant correlation between Reynolds number and characteristics of the velocity power spectra is observed

Shielding walls against ionizing radiation

International Nuclear Information System (INIS)

1993-05-01

Hot-cell shielding walls consist of building blocks made of lead according to DIN 25407 part 1, and of special elements according to DIN 25407 part 2. Alpha-gamma cells can be built using elements for protective contamination boxes according to DIN 25480 part 1. This standards document intends to provide planning engineers, manufacturers, future users and the competent authorities and experts with a basis for the design of hot cells with lead shielding walls and the design of hot-cell equipment. (orig./HP) [de

Implantation doping of GaN

International Nuclear Information System (INIS)

Zolper, J.C.

1996-01-01

Ion implantation has played an enabling role in the realization of many high performance photonic and electronic devices in mature semiconductor materials systems such as Si and GaAs. This can also be expected to be the case in III-Nitride based devices as the material quality continues to improve. This paper reviews the progress in ion implantation processing of the III-Nitride materials, namely, GaN, AlN, InN and their alloys. Details are presented of the successful demonstrations of implant isolation as well as n- and p-type implantation doping of GaN. Implant doping has required activation annealing at temperatures in excess of 1,000 C. The nature of the implantation induced damage and its response to annealing is addressed using Rutherford Backscattering. Finally, results are given for the first demonstration of a GaN device fabricated using ion implantation doping, a GaN junction field effect transistor (JFET)

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

International Nuclear Information System (INIS)

Choi, Yunju; Kim, Yangsoo; Ahn, Kwang-Soon; Kim, Hyunsoo

2014-01-01

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10 −3 , 4.3 × 10 −4 , and 1.1 × 10 −3 Ω cm 2 for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N 2 ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples

Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

Energy Technology Data Exchange (ETDEWEB)

Choi, Yunju [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Kim, Yangsoo [Suncheon Center, Korea Basic Science Institute, Suncheon 540-742 (Korea, Republic of); Ahn, Kwang-Soon, E-mail: kstheory@ynu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 712-749 (Korea, Republic of); Kim, Hyunsoo, E-mail: hskim7@jbnu.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

2014-10-30

Highlights: • The Cr/Au contact on n-type Ga-polar (0 0 0 1) GaN, N-polar (0 0 0 −1) GaN, and wet-etched N-polar GaN were investigated. • Thermal annealing led to a significant degradation of contact formed on N-polar n-GaN samples. • Contact degradation was shown to be closely related to the increase in the electrical resistivity of n-GaN. • Out-diffusion of Ga and N atoms was clearly observed in N-polar samples. - Abstract: The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10{sup −3}, 4.3 × 10{sup −4}, and 1.1 × 10{sup −3} Ω cm{sup 2} for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N{sub 2} ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples.

Improved crystal quality of a-plane GaN with high- temperature 3-dimensional GaN buffer layers deposited by using metal-organic chemical vapor deposition

International Nuclear Information System (INIS)

Park, Sung Hyun; Moon, Dae Young; Kim, Bum Ho; Kim, Dong Uk; Chang, Ho Jun; Jeon, Heon Su; Yoon, Eui Joon; Joo, Ki Su; You, Duck Jae; Nanishi, Yasushi

2012-01-01

a-plane GaN on r-plane sapphire substrates suffers from high density defects and rough surfaces. To obtain pit-free a-plane GaN by metal-organic chemical vapor deposition, we intentionally grew high-temperature (HT) 3-dimensional (3D) GaN buffer layers on a GaN nucleation layer. The effects of the HT 3D GaN buffer layers on crystal quality and the surface morphology of a-plane GaN were studied. The insertion of a 3D GaN buffer layer with an optimum thickness was found to be an effective method to obtain pit-free a-plane GaN with improved crystalline quality on r-plane sapphire substrates. An a-plane GaN light emitting diode (LED) at an emission wavelength around 480 nm with negligible peak shift was successfully fabricated.

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

Science.gov (United States)

Zúñiga-Pérez, Jesús; Consonni, Vincent; Lymperakis, Liverios; Kong, Xiang; Trampert, Achim; Fernández-Garrido, Sergio; Brandt, Oliver; Renevier, Hubert; Keller, Stacia; Hestroffer, Karine; Wagner, Markus R.; Reparaz, Juan Sebastián; Akyol, Fatih; Rajan, Siddharth; Rennesson, Stéphanie; Palacios, Tomás; Feuillet, Guy

2016-12-01

The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade.

Performance of CVD and CVR coated carbon-carbon in high temperature hydrogen

Science.gov (United States)

Adams, J. W.; Barletta, R. E.; Svandrlik, J.; Vanier, P. E.

As a part of the component development process for the particle bed reactor (PBR), it is necessary to develop coatings which will be time and temperature stable at extremely high temperatures in flowing hydrogen. These coatings must protect the underlying carbon structure from attack by the hydrogen coolant. Degradation which causes small changes in the reactor component, e.g. hole diameter in the hot frit, can have a profound effect on operation. The ability of a component to withstand repeated temperature cycles is also a coating development issue. Coatings which crack or spall under these conditions would be unacceptable. While refractory carbides appear to be the coating material of choice for carbon substrates being used in PBR components, the method of applying these coatings can have a large effect on their performance. Two deposition processes for these refractory carbides, chemical vapor deposition (CVD) and chemical vapor reaction (CVR), have been evaluated. Screening tests for these coatings consisted of testing of coated 2-D and 3-D weave carbon-carbon in flowing hot hydrogen at one atmosphere. Carbon loss from these samples was measured as a function of time. Exposure temperatures up to 3,000 K were used, and samples were exposed in a cyclical fashion cooling to room temperature between exposures. The results of these measurements are presented along with an evaluation of the relative merits of CVR and CVD coatings for this application.

Influence of substrate material on the microstructure and optical properties of hot wall deposited SnS thin films

International Nuclear Information System (INIS)

Bashkirov, S.A.; Gremenok, V.F.; Ivanov, V.A.; Shevtsova, V.V.; Gladyshev, P.P.

2015-01-01

Tin monosulfide SnS raises an interest as a promising material for photovoltaics. The influence of the substrate material on the microstructure and optical properties of SnS thin films with [111] texture obtained by hot wall vacuum deposition on glass, molybdenum and indium tin oxide substrates is reported. The lattice parameters for layers grown on different substrates were determined by X-ray diffraction and their deviations from the data reported in the literature for single α-SnS crystals were discussed. The change in the degree of preferred orientation of the films depending on the substrate material is observed. The direct nature of the optical transitions with the optical band gap of 1.15 ± 0.01 eV is reported. - Highlights: • SnS thin films were hot wall deposited on glass, molybdenum and indium tin oxide. • Physical properties of the films were studied with respect to the substrate type. • The SnS lattice parameter deviations were observed and the explanation was given. • The direct optical transitions with the band gap of 1.15 ± 0.01 eV were observed

CVD diamond substrates for electronic devices

International Nuclear Information System (INIS)

Holzer, H.

1996-03-01

In this study the applicability of chemical vapor deposition (CVD) diamond as a material for heat spreaders was investigated. Economical evaluations on the production of heat spreaders were also performed. For the diamond synthesis the hot-filament and microwave method were used respectively. The deposition parameters were varied in a way that free standing diamond layers with a thickness of 80 to 750 microns and different qualities were obtained. The influence of the deposition parameters on the relevant film properties was investigated and discussed. With both the hot-filament and microwave method it was possible to deposit diamond layers having a thermal conductivity exceeding 1200 W/mK and therefore to reach the quality level for commercial uses. The electrical resistivity was greater than 10 12 Ωcm. The investigation of the optical properties was done by Raman-, IR- and cathodoluminescence spectroscopy. Because of future applications of diamond-aluminium nitride composites as highly efficient heat spreaders diamond deposition an AIN was investigated. An improved substrate pretreatment prior to diamond deposition showed promising results for better performance of such composite heat spreaders. Both free standing layers and diamond-AIN composites could be cut by a CO2 Laser in Order to get an exact size geometry. A reduction of the diamond surface roughness was achieved by etching with manganese powder or cerium. (author)

Influence of tungsten on the carbon nanotubes growth by CVD process

Energy Technology Data Exchange (ETDEWEB)

Escobar, Mariano [Instituto de Fisicoquimica de Materiales, Ambiente y Energia, CONICET-UBA, Pabellon II, Ciudad Universitaria (1428) Bs As (Argentina); LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina)], E-mail: mescobar@qi.fcen.uba.ar; Rubiolo, Gerardo H. [LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina); Unidad de Actividad Materiales, CNEA, Av. Gral. Paz 1499, San Martin (1650), Bs As (Argentina); Moreno, M. Sergio [Centro Atomico Bariloche, (8400) S.C. de Bariloche, Rio Negro (Argentina); Goyanes, Silvia [LP and MC, Dep. De Fisica, FCEyN-UBA, Pabellon 1, Ciudad Universitaria (1428) Bs As (Argentina); Candal, Roberto [Instituto de Fisicoquimica de Materiales, Ambiente y Energia, CONICET-UBA, Pabellon II, Ciudad Universitaria (1428) Bs As (Argentina)

2009-06-24

The effect of tungsten (W) on the growth of multi-walled carbon nanotubes (MWNTs) using the chemical vapour deposition (CVD) process over a metal Fe-W catalyst incorporated into a silica matrix is reported. A W molar content in Fe/SiO{sub 2} up to 10% was studied. The incorporation of only 2% of W substantially modifies the crystalline phases and the crystalline degree of the catalyst during the MWNTs synthesis. This fact seems to have a strong influence on the type and yield of the carbonaceous species obtained by the CVD of acetylene, at 600 deg. C and 180 Torr, over each catalyst. Tungsten interacts with iron within the matrix, diminishing the catalytic activity of the metal nanoparticles, and both, carbon nanotubes and carbon nanofibers, are obtained when tungsten is present. The results obtained support the hypothesis of a base growth model for carbon nanotubes indicating a strong interaction between silica matrix and Fe/W nanoparticles, independently of the content of W.

Influence of tungsten on the carbon nanotubes growth by CVD process

International Nuclear Information System (INIS)

Escobar, Mariano; Rubiolo, Gerardo H.; Moreno, M. Sergio; Goyanes, Silvia; Candal, Roberto

2009-01-01

The effect of tungsten (W) on the growth of multi-walled carbon nanotubes (MWNTs) using the chemical vapour deposition (CVD) process over a metal Fe-W catalyst incorporated into a silica matrix is reported. A W molar content in Fe/SiO 2 up to 10% was studied. The incorporation of only 2% of W substantially modifies the crystalline phases and the crystalline degree of the catalyst during the MWNTs synthesis. This fact seems to have a strong influence on the type and yield of the carbonaceous species obtained by the CVD of acetylene, at 600 deg. C and 180 Torr, over each catalyst. Tungsten interacts with iron within the matrix, diminishing the catalytic activity of the metal nanoparticles, and both, carbon nanotubes and carbon nanofibers, are obtained when tungsten is present. The results obtained support the hypothesis of a base growth model for carbon nanotubes indicating a strong interaction between silica matrix and Fe/W nanoparticles, independently of the content of W.

Controlling the number of walls in multi walled carbon nanotubes/alumina hybrid compound via ball milling of precipitate catalyst

Energy Technology Data Exchange (ETDEWEB)

Nosbi, Norlin [School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia (USM), 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang (Malaysia); Akil, Hazizan Md, E-mail: hazizan@usm.my [School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia (USM), 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang (Malaysia); Cluster for Polymer Composite (CPC), Science and Engineering Research Centre, Engineering Campus, Universiti Sains Malaysia (USM), 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang (Malaysia)

2015-06-15

Graphical abstract: - Highlights: • We report that, to manipulate carbon nanotubes geometry and number of walls are by controlling the precipitate catalyst size. • Number of walls and geometry effects depend on the milling time of the precipitate catalyst. • Increasing milling of time will decrease the carbon nanotubes number of walls. • Increasing milling of time will increase the carbon nanotubes thermal conductivity. - Abstract: This paper reports the influence of milling time on the structure and properties of the precipitate catalyst of multi walled carbon nanotubes (MWCNT)/alumina hybrid compound, produced through the chemical vapour deposition (CVD) process. For this purpose, light green precipitate consisted of aluminium, nickel(II) nitrate hexahydrate and sodium hydroxide mixture was placed in a planetary mill equipped with alumina vials using alumina balls at 300 rpm rotation speed for various milling time (5–15 h) prior to calcinations and CVD process. The compound was characterized using various techniques. Based on high-resolution transmission electron microscopy analysis, increasing the milling time up to 15 h decreased the diameter of MWCNT from 32.3 to 13.1 nm. It was noticed that the milling time had a significant effect on MWCNT wall thickness, whereby increasing the milling time from 0 to 15 h reduced the number of walls from 29 to 12. It was also interesting to note that the carbon content increased from 23.29 wt.% to 36.37 wt.% with increasing milling time.

GaN Nanowire Arrays for High-Output Nanogenerators

KAUST Repository

Huang, Chi-Te

2010-04-07

Three-fold symmetrically distributed GaN nanowire (NW) arrays have been epitaxially grown on GaN/sapphire substrates. The GaN NW possesses a triangular cross section enclosed by (0001), (2112), and (2112) planes, and the angle between the GaN NW and the substrate surface is ∼62°. The GaN NW arrays produce negative output voltage pulses when scanned by a conductive atomic force microscope in contact mode. The average of piezoelectric output voltage was about -20 mV, while 5-10% of the NWs had piezoelectric output voltages exceeding -(0.15-0.35) V. The GaN NW arrays are highly stable and highly tolerate to moisture in the atmosphere. The GaN NW arrays demonstrate an outstanding potential to be utilized for piezoelectric energy generation with a performance probably better than that of ZnO NWs. © 2010 American Chemical Society.

Rewetting phenomena and their relation to intermolecular forces between a hot wall and the fluid

International Nuclear Information System (INIS)

Gerweck, V.

1989-12-01

The rewetting phenomena and the different physical concepts which are used in their modelisation are reviewed. The present work studies the effect of the intermolecular forces between the hot wall and the fluid on this phase transition. Using suitable approximations, a local equation of state is obtained by the treatment of the fluid-fluid and fluid-wall intermolecular interactions. This local equation of state depends on the distance from the wall, and the critical pressure and temperature become a function of the distance from the wall, whereas the critical density is left constant throughout the fluid. At the wall, the critical pressure and temperature are half their bulk values and increase towards the bulk value as the distance from the wall increases. The penetration of a temperature profile in this fluid is studied by assuming that the liquid density is not strongly affected by this temperature profile as long as there is no phase transition. It is shown that the phase transition will occur extremely rapidly when the interfacial temperature upon contact is higher than the minimum of the local spinodal temperature, which varies with the distance from the wall. The result ist cast in the form of an interfacial rewetting temperature fT c above which rewetting of the surface by liquid-wall contacts is not expected because these contacts will be terminated in extremely short times. Comparing the theory with available data shows that in the usual rewetting situations the theory reduces to the use of the bulk spinodal temperature. For surfaces coated with poorly wetted materials the correction factor due to surface effects applies, reducing the rewetting temperature, in agreement with the experimental data. For liquid metals it appears that the theory is applied in a region where the basic theoretical approximations are very coarse; but even in that case the experimental trend is qualitatively predicted by the theory. (author) 43 figs., 11 tabs., 105 refs

Hot gas path component having near wall cooling features

Science.gov (United States)

Miranda, Carlos Miguel; Kottilingam, Srikanth Chandrudu; Lacy, Benjamin Paul

2017-11-28

A method for providing micro-channels in a hot gas path component includes forming a first micro-channel in an exterior surface of a substrate of the hot gas path component. A second micro-channel is formed in the exterior surface of the hot gas path component such that it is separated from the first micro-channel by a surface gap having a first width. The method also includes disposing a braze sheet onto the exterior surface of the hot gas path component such that the braze sheet covers at least of portion of the first and second micro-channels, and heating the braze sheet to bond it to at least a portion of the exterior surface of the hot gas path component.

Silicon—a new substrate for GaN growth

Indian Academy of Sciences (India)

Unknown

of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the .... Considerable research is being carried out on GaN HEMTs at present. ... by InGaN/GaN multiquantum well in MOVPE was first.

Photoluminescence of Mg-doped m-plane GaN grown by MOCVD on bulk GaN substrates

OpenAIRE

Monemar, Bo; Paskov, Plamen; Pozina, Galia; Hemmingsson, Carl; Bergman, Peder; Lindgren, David; Samuelson, Lars; Ni, Xianfeng; Morkoç, Hadis; Paskova, Tanya; Bi, Zhaoxia; Ohlsson, Jonas

2011-01-01

Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 1018cm-3 to well above 1019 cm-3. The samples were grown with MOCVD at reduced pressure on low defect density m-plane bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9 eV to 3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependenc...

Hot wire production of single-wall and multi-wall carbon nanotubes

Science.gov (United States)

Dillon, Anne C.; Mahan, Archie H.; Alleman, Jeffrey L.

2010-10-26

Apparatus (210) for producing a multi-wall carbon nanotube (213) may comprise a process chamber (216), a furnace (217) operatively associated with the process chamber (216), and at least one filament (218) positioned within the process chamber (216). At least one power supply (220) operatively associated with the at least one filament (218) heats the at least one filament (218) to a process temperature. A gaseous carbon precursor material (214) operatively associated with the process chamber (216) provides carbon for forming the multi-wall carbon nanotube (213). A metal catalyst material (224) operatively associated with the process (216) catalyzes the formation of the multi-wall carbon nanotube (213).

Oxide Dispersion Strengthened Iron Aluminide by CVD Coated Powders

Energy Technology Data Exchange (ETDEWEB)

Asit Biswas Andrew J. Sherman

2006-09-25

This I &I Category2 program developed chemical vapor deposition (CVD) of iron, aluminum and aluminum oxide coated iron powders and the availability of high temperature oxidation, corrosion and erosion resistant coating for future power generation equipment and can be used for retrofitting existing fossil-fired power plant equipment. This coating will provide enhanced life and performance of Coal-Fired Boilers components such as fire side corrosion on the outer diameter (OD) of the water wall and superheater tubing as well as on the inner diameter (ID) and OD of larger diameter headers. The program also developed a manufacturing route for readily available thermal spray powders for iron aluminide coating and fabrication of net shape component by powder metallurgy route using this CVD coated powders. This coating can also be applid on jet engine compressor blade and housing, industrial heat treating furnace fixtures, magnetic electronic parts, heating element, piping and tubing for fossil energy application and automotive application, chemical processing equipment , heat exchanger, and structural member of aircraft. The program also resulted in developing a new fabrication route of thermal spray coating and oxide dispersion strengthened (ODS) iron aluminide composites enabling more precise control over material microstructures.

Epitaxial GaN around ZnO nanopillars

Energy Technology Data Exchange (ETDEWEB)

Fikry, Mohamed; Scholz, Ferdinand [Institut fuer Optoelektronik, Universitaet Ulm, Albert-Einstein-Allee 45, 89081 Ulm (Germany); Madel, Manfred; Tischer, Ingo; Thonke, Klaus [Institut fuer Quantenmaterie, Universitaet Ulm, Albert-Einstein-Allee 45, 89081 Ulm (Germany)

2011-07-01

We report on an investigation of the epitaxial quality of GaN layers overgrown coaxially around ZnO nanopillars. In a first step, regularly arranged ZnO nanopillars were grown using pre-patterning by e-beam lithography or self-organized hexagonal polystyrene sphere masks. Alternatively, ZnO pillars were also successfully grown on top of GaN pyramids. In a second step, GaN layers were grown around the ZnO pillars by Metal Organic Vapor Phase Epitaxy. At growth temperatures above 800 C, the ZnO pillars are dissolved by the hydrogen carrier gas leaving hollow GaN nanotubes. Characterization involved photoluminescence (PL), scanning electron microscopy and cathodoluminescence. The fair quality of the deposited GaN layers is confirmed by a sharp low temperature PL peak at 3.48 eV attributed to the donor bound exciton emission. Further peaks at 3.42 eV and 3.29 eV show the possible existence of basal plane and prismatic stacking faults.

Dislocation-induced nanoparticle decoration on a GaN nanowire.

Science.gov (United States)

Yang, Bing; Yuan, Fang; Liu, Qingyun; Huang, Nan; Qiu, Jianhang; Staedler, Thorsten; Liu, Baodan; Jiang, Xin

2015-02-04

GaN nanowires with homoepitaxial decorated GaN nanoparticles on their surface along the radial direction have been synthesized by means of a chemical vapor deposition method. The growth of GaN nanowires is catalyzed by Au particles via the vapor-liquid-solid (VLS) mechanism. Screw dislocations are generated along the radial direction of the nanowires under slight Zn doping. In contrast to the metal-catalyst-assisted VLS growth, GaN nanoparticles are found to prefer to nucleate and grow at these dislocation sites. High-resolution transmission electron microscopy (HRTEM) analysis demonstrates that the GaN nanoparticles possess two types of epitaxial orientation with respect to the corresponding GaN nanowire: (I) [1̅21̅0]np//[1̅21̅0]nw, (0001)np//(0001)nw; (II) [1̅21̅3]np//[12̅10]nw, (101̅0)np//(101̅0)nw. An increased Ga signal in the energy-dispersive spectroscopy (EDS) profile lines of the nanowires suggests GaN nanoparticle growth at the edge surface of the wires. All the crystallographic results confirm the importance of the dislocations with respect to the homoepitaxial growth of the GaN nanoparticles. Here, screw dislocations situated on the (0001) plane provide the self-step source to enable nucleation of the GaN nanoparticles.

Large electron capture-cross-section of the major nonradiative recombination centers in Mg-doped GaN epilayers grown on a GaN substrate

Science.gov (United States)

Chichibu, S. F.; Shima, K.; Kojima, K.; Takashima, S.; Edo, M.; Ueno, K.; Ishibashi, S.; Uedono, A.

2018-05-01

Complementary time-resolved photoluminescence and positron annihilation measurements were carried out at room temperature on Mg-doped p-type GaN homoepitaxial films for identifying the origin and estimating the electron capture-cross-section ( σ n ) of the major nonradiative recombination centers (NRCs). To eliminate any influence by threading dislocations, free-standing GaN substrates were used. In Mg-doped p-type GaN, defect complexes composed of a Ga-vacancy (VGa) and multiple N-vacancies (VNs), namely, VGa(VN)2 [or even VGa(VN)3], are identified as the major intrinsic NRCs. Different from the case of 4H-SiC, atomic structures of intrinsic NRCs in p-type and n-type GaN are different: VGaVN divacancies are the major NRCs in n-type GaN. The σ n value approximately the middle of 10-13 cm2 is obtained for VGa(VN)n, which is larger than the hole capture-cross-section (σp = 7 × 10-14 cm2) of VGaVN in n-type GaN. Combined with larger thermal velocity of an electron, minority carrier lifetime in Mg-doped GaN becomes much shorter than that of n-type GaN.

Synthesis of p-type GaN nanowires.

Science.gov (United States)

Kim, Sung Wook; Park, Youn Ho; Kim, Ilsoo; Park, Tae-Eon; Kwon, Byoung Wook; Choi, Won Kook; Choi, Heon-Jin

2013-09-21

GaN has been utilized in optoelectronics for two decades. However, p-type doping still remains crucial for realization of high performance GaN optoelectronics. Though Mg has been used as a p-dopant, its efficiency is low due to the formation of Mg-H complexes and/or structural defects in the course of doping. As a potential alternative p-type dopant, Cu has been recognized as an acceptor impurity for GaN. Herein, we report the fabrication of Cu-doped GaN nanowires (Cu:GaN NWs) and their p-type characteristics. The NWs were grown vertically via a vapor-liquid-solid (VLS) mechanism using a Au/Ni catalyst. Electrical characterization using a nanowire-field effect transistor (NW-FET) showed that the NWs exhibited n-type characteristics. However, with further annealing, the NWs showed p-type characteristics. A homo-junction structure (consisting of annealed Cu:GaN NW/n-type GaN thin film) exhibited p-n junction characteristics. A hybrid organic light emitting diode (OLED) employing the annealed Cu:GaN NWs as a hole injection layer (HIL) also demonstrated current injected luminescence. These results suggest that Cu can be used as a p-type dopant for GaN NWs.

CVD-graphene for low equivalent series resistance in rGO/CVD-graphene/Ni-based supercapacitors

Science.gov (United States)

Kwon, Young Hwi; Kumar, Sunil; Bae, Joonho; Seo, Yongho

2018-05-01

Reduced equivalent series resistance (ESR) is necessary, particularly at a high current density, for high performance supercapacitors, and the interface resistance between the current collector and electrode material is one of the main components of ESR. In this report, we have optimized chemical vapor deposition-grown graphene (CVD-G) on a current collector (Ni-foil) using reduced graphene oxide as an active electrode material to fabricate an electric double layer capacitor with reduced ESR. The CVD-G was grown at different cooling rates—20 °C min‑1, 40 °C min‑1 and 100 °C min‑1—to determine the optimum conditions. The lowest ESR, 0.38 Ω, was obtained for a cell with a 100 °C min‑1 cooling rate, while the sample without a CVD-G interlayer exhibited 0.80 Ω. The CVD-G interlayer-based supercapacitors exhibited fast CD characteristics with high scan rates up to 10 Vs‑1 due to low ESR. The specific capacitances deposited with CVD-G were in the range of 145.6 F g‑1–213.8 F g‑1 at a voltage scan rate of 0.05 V s‑1. A quasi-rectangular behavior was observed in the cyclic voltammetry curves, even at very high scan rates of 50 and 100 V s‑1, for the cell with optimized CVD-G at higher cooling rates, i.e. 100 °C min‑1.

Development of TiC coated wall materials for JT-60

International Nuclear Information System (INIS)

Abe, T.; Murakami, Y.; Obara, K.; Hiroki, S.; Nakamura, K.; Inagawa, K.

1985-01-01

Development of titanium carbide (TiC, 20 μm thick) coated wall materials has been carried out for JT-60. Application of TiC coatings onto molybdenum and Inconel 625 substrates requires a deposition temperature below 950 0 C and 600 0 C respectively, because recrystallization of molybdenum and age hardening of Inconel 625 occur above these temperatures. Through this process of coating we develop a new type plasma CVD(TP-CVD method) for molybdenum and a new type PVD(HCD-ARE method) for Inconel 625 which could successfully reduce the deposition temperature to 900 0 C and 500 0 C, respectively. The TiC coated wall samples were characterized by AES, ESCA, X-ray diffractometer, EPMA, SEM, metalography, tensile tests, thermal shock tests, and other techniques. As a result of the above measurements, it was demonstrated that the characteristics of those TiC coated walls satisfy the requirements arising from JT-60 operation conditions. (orig.)

Interaction of GaN epitaxial layers with atomic hydrogen

Energy Technology Data Exchange (ETDEWEB)

Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G.; Namkoong, G.; Doolittle, W.A.; Brown, A.S

2004-08-15

GaN surface passivation processes are still under development and among others hydrogen treatments are investigated. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry (SE) and surface potential Kelvin probe microscopy (SP-KPM) in conjunction with non-contact atomic force microscopy (AFM) for the study of the different reactivity of Ga-polar and N-polar GaN epitaxial layers with atomic hydrogen. The GaN epitaxial layers are grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates, and GaN and AlN buffer layers are used to grow N-polar and Ga-polar films, respectively. The atomic hydrogen is produced by a remote rf (13.56 MHz) H{sub 2} plasma in order to rule out any ion bombardment of the GaN surface and make the interaction chemical. It is found that the interaction of GaN surfaces with atomic hydrogen depends on polarity, with N-polar GaN exhibiting greater reactivity. Furthermore, it is found that atomic hydrogen is effective in the passivation of grain boundaries and surface defects states.

Interaction of GaN epitaxial layers with atomic hydrogen

International Nuclear Information System (INIS)

Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G.; Namkoong, G.; Doolittle, W.A.; Brown, A.S.

2004-01-01

GaN surface passivation processes are still under development and among others hydrogen treatments are investigated. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry (SE) and surface potential Kelvin probe microscopy (SP-KPM) in conjunction with non-contact atomic force microscopy (AFM) for the study of the different reactivity of Ga-polar and N-polar GaN epitaxial layers with atomic hydrogen. The GaN epitaxial layers are grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates, and GaN and AlN buffer layers are used to grow N-polar and Ga-polar films, respectively. The atomic hydrogen is produced by a remote rf (13.56 MHz) H 2 plasma in order to rule out any ion bombardment of the GaN surface and make the interaction chemical. It is found that the interaction of GaN surfaces with atomic hydrogen depends on polarity, with N-polar GaN exhibiting greater reactivity. Furthermore, it is found that atomic hydrogen is effective in the passivation of grain boundaries and surface defects states

Induced defects in neutron irradiated GaN single crystals

International Nuclear Information System (INIS)

Park, I. W.; Koh, E. K.; Kim, Y. M.; Choh, S. H.; Park, S. S.; Kim, B. G.; Sohn, J. M.

2005-01-01

The local structure of defects in undoped, Si-doped, and neutron irradiated free standing GaN bulk crystals, grown by hydride vapor phase epitaxy, has been investigated by employing Raman scattering and cathodoluminescence. The GaN samples were irradiated to a dose of 2 x 10 17 neutrons in an atomic reactor at Korea Atomic Energy Research Institute. There was no appreciable change in the Raman spectra for undoped GaN samples before and after neutron irradiation. However, a forbidden transition, A 1 (TO) mode, appeared for a neutron irradiated Si-doped GaN crystal. Cathodoluminescence spectrum for the neutron irradiated Si-doped GaN crystal became much more broadened than that for the unirradiated one. The experimental results reveal the generation of defects with locally deformed structure in the wurtzite Si-doped GaN single crystal

Sub-bandgap optical absorption spectroscopy of hydrogenated microcrystalline silicon thin films prepared using hot-wire CVD (Cat-CVD) process

International Nuclear Information System (INIS)

Goktas, O.; Isik, N.; Okur, S.; Gunes, M.; Carius, R.; Klomfass, J.; Finger, F.

2006-01-01

Hydrogenated microcrystalline silicon (μc-Si:H) thin films with different silane concentration (SC) have been prepared using the HW-CVD technique. Dual beam photoconductivity (DBP), photothermal deflection spectroscopy (PDS), and transmission measurements have been used to investigate the optical properties of the μc-Si:H films. Two different sub-bandgap absorption, α(hν), methods have been applied and analyzed to obtain a better insight into the electronic states involved. A good agreement has been obtained in the absorption spectrum obtained from the PDS and DBP measurements at energies above the bandgap. Differences between PDS and DBP spectra exist below the bandgap energy where DBP spectra always give lower α(hν) values and show a dependence on the SC. For some films, differences exist in the α(hν) spectra when the DBP measurements are carried out through the film and substrate side. In addition, for some films, there remains fringe pattern left on the spectrum after the calculation of the fringe-free absorption spectrum, which indicates structural inhomogeneities present throughout the film

Turbostratic stacked CVD graphene for high-performance devices

Science.gov (United States)

Uemura, Kohei; Ikuta, Takashi; Maehashi, Kenzo

2018-03-01

We have fabricated turbostratic stacked graphene with high-transport properties by the repeated transfer of CVD monolayer graphene. The turbostratic stacked CVD graphene exhibited higher carrier mobility and conductivity than CVD monolayer graphene. The electron mobility for the three-layer turbostratic stacked CVD graphene surpassed 10,000 cm2 V-1 s-1 at room temperature, which is five times greater than that for CVD monolayer graphene. The results indicate that the high performance is derived from maintenance of the linear band dispersion, suppression of the carrier scattering, and parallel conduction. Therefore, turbostratic stacked CVD graphene is a superior material for high-performance devices.

ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

Energy Technology Data Exchange (ETDEWEB)

Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C

2011-04-11

The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

Interfaces in hot gauge theory

CERN Document Server

Bronoff, S.

1996-01-01

The string tension at low T and the free energy of domain walls at high T can be computed from one and the same observable. We show by explicit calculation that domain walls in hot Z(2) gauge theory have good thermodynamical behaviour. This is due to roughening of the wall, which expresses the restoration of translational symmetry.

Polarization Raman spectroscopy of GaN nanorod bundles

International Nuclear Information System (INIS)

Tite, T.; Lee, C. J.; Chang, Y.-M.

2010-01-01

We performed polarization Raman spectroscopy on single wurtzite GaN nanorod bundles grown by plasma-assisted molecular beam epitaxy. The obtained Raman spectra were compared with those of GaN epilayer. The spectral difference between the GaN nanorod bundles and epilayer reveals the relaxation of Raman selection rules in these GaN nanorod bundles. The deviation of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules is attributed to both the orientation of the crystal axis with respect to the polarization vectors of incident and scattered light and the structural defects in the merging boundary of GaN nanorods. The presence of high defect density induced by local strain at the merging boundary was further confirmed by transmission electron microscopy. The averaged defect interspacing was estimated to be around 3 nm based on the spatial correlation model.

Computational study of GaAs1-xNx and GaN1-yAsy alloys and arsenic impurities in GaN

International Nuclear Information System (INIS)

Laaksonen, K; Komsa, H-P; Arola, E; Rantala, T T; Nieminen, R M

2006-01-01

We have studied the structural and electronic properties of As-rich GaAs 1-x N x and N-rich GaN 1-y As y alloys in a large composition range using first-principles methods. We have systematically investigated the effect of the impurity atom configuration near both GaAs and GaN sides of the concentration range on the total energies, lattice constants and bandgaps. The N (As) atoms, replacing substitutionally As (N) atoms in GaAs (GaN), cause the surrounding Ga atoms to relax inwards (outwards), making the Ga-N (Ga-As) bond length about 15% shorter (longer) than the corresponding Ga-As (Ga-N) bond length in GaAs (GaN). The total energies of the relaxed alloy supercells and the bandgaps experience large fluctuations within different configurations and these fluctuations grow stronger if the impurity concentration is increased. Substituting As atoms with N in GaAs induces modifications near the conduction band minimum, while substituting N atoms with As in GaN modifies the states near the valence band maximum. Both lead to bandgap reduction, which is at first rapid but later slows down. The relative size of the fluctuations is much larger in the case of GaAs 1-x N x alloys. We have also looked into the question of which substitutional site (Ga or N) As occupies in GaN. We find that under Ga-rich conditions arsenic prefers the substitutional N site over the Ga site within a large range of Fermi level values

Determination of carrier diffusion length in GaN

Science.gov (United States)

Hafiz, Shopan; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit; Metzner, Sebastian; Bertram, Frank; Christen, Jürgen; Gil, Bernard

2015-01-01

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) and cross-sectional cathodoluminescence (CL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p-GaN or 1500 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photo-generation near the surface region by above bandgap excitation. Taking into consideration the absorption in the top GaN layer as well as active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be 93 ± 7 nm and 70 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively, at photogenerated carrier densities of 4.2 × 1018 cm-3 using PL spectroscopy. CL measurements of the unintentionally doped n-type GaN layer at much lower carrier densities of 1017 cm-3 revealed a longer diffusion length of 525 ± 11 nm at 6 K.

Schottky contacts to polar and nonpolar n-type GaN

Energy Technology Data Exchange (ETDEWEB)

Kim, Hogyoung [Hanbat National University, Daejeon (Korea, Republic of); Phark, Soohyon [Max-Planck-Institut fur Mikrostrukturphysik, Halle (Germany); Song, Keunman [Korea Advanced Nano Fab Center, Suwon (Korea, Republic of); Kim, Dongwook [Ewha Woman' s University, Seoul (Korea, Republic of)

2012-01-15

Using the current-voltage measurements, we observed the barrier heights of c-plane GaN in Pt and Au Schottky contacts to be higher than those of a-plane GaN. However, the barrier height of c-plane GaN was lower than that of a-plane GaN in the Ti Schottky contacts. The N/Ga ratio calculated by integrating the X-ray photoelectron spectroscopy (XPS) spectra of Ga 3d and N 1s core levels showed that c-plane GaN induced more Ga vacancies near the interface than a-plane GaN in the Ti Schottky contacts, reducing the effective barrier height through an enhancement of the tunneling probability.

The trap states in lightly Mg-doped GaN grown by MOVPE on a freestanding GaN substrate

Science.gov (United States)

Narita, Tetsuo; Tokuda, Yutaka; Kogiso, Tatsuya; Tomita, Kazuyoshi; Kachi, Tetsu

2018-04-01

We investigated traps in lightly Mg-doped (2 × 1017 cm-3) p-GaN fabricated by metalorganic vapor phase epitaxy (MOVPE) on a freestanding GaN substrate and the subsequent post-growth annealing, using deep level transient spectroscopy. We identified four hole traps with energy levels of EV + 0.46, 0.88, 1.0, and 1.3 eV and one electron trap at EC - 0.57 eV in a p-type GaN layer uniformly doped with magnesium (Mg). The Arrhenius plot of hole traps with the highest concentration (˜3 × 1016 cm-3) located at EV + 0.88 eV corresponded to those of hole traps ascribed to carbon on nitrogen sites in n-type GaN samples grown by MOVPE. In fact, the range of the hole trap concentrations at EV + 0.88 eV was close to the carbon concentration detected by secondary ion mass spectroscopy. Moreover, the electron trap at EC - 0.57 eV was also identical to the dominant electron traps commonly observed in n-type GaN. Together, these results suggest that the trap states in the lightly Mg-doped GaN grown by MOVPE show a strong similarity to those in n-type GaN, which can be explained by the Fermi level close to the conduction band minimum in pristine MOVPE grown samples due to existing residual donors and Mg-hydrogen complexes.

Photoluminescence of Mg-doped m-plane GaN grown by MOCVD on bulk GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Monemar, Bo [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Solid State Physics-The Nanometer Structure Consortium, Lund University, Box 118, 221 00 Lund (Sweden); Paskov, Plamen; Pozina, Galia; Hemmingsson, Carl; Bergman, Peder [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Lindgren, David; Samuelson, Lars [Solid State Physics-The Nanometer Structure Consortium, Lund University, Box 118, 221 00 Lund (Sweden); Ni, Xianfeng; Morkoc, Hadis [Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3072 (United States); Paskova, Tanya [Kyma Technologies Inc., Raleigh, North Carolina 27617 (United States); Bi, Zhaoxia; Ohlsson, Jonas [Glo AB, Ideon Science Park, Scheelevaegen 17, 223 70 Lund (Sweden)

2011-07-15

Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 10{sup 18} cm{sup -3} to above 10{sup 20} cm{sup -3}. The samples were grown with MOCVD at reduced pressure on low defect density bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9-3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependence of the BE spectra on excitation intensity as well as the transient decay behaviour demonstrate acoustic phonon assisted transfer between the acceptor BE states. The lower energy donor-acceptor pair spectra suggest the presence of deep acceptors, in addition to the two main shallower ones at about 0.23 eV. Similar spectra from Mg-doped GaN nanowires (NWs) grown by MOCVD are also briefly discussed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

GaN epitaxial layers grown on multilayer graphene by MOCVD

Science.gov (United States)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe

2018-04-01

In this study, GaN epitaxial layers were successfully deposited on a multilayer graphene (MLG) by using metal-organic chemical vapor deposition (MOCVD). Highly crystalline orientations of the GaN films were confirmed through electron backscatter diffraction (EBSD). An epitaxial relationship between GaN films and MLG is unambiguously established by transmission electron microscope (TEM) analysis. The Raman spectra was used to analyze the internal stress of GaN films, and the spectrum shows residual tensile stress in the GaN films. Moreover, the results of the TEM analysis and Raman spectra indicate that the high quality of the MLG substrate is maintained even after the growth of the GaN film. This high-quality MLG makes it possible to easily remove epitaxial layers from the supporting substrate by micro-mechanical exfoliation technology. This work can aid in the development of transferable devices using GaN films.

Influencing factors of GaN growth uniformity through orthogonal test analysis

International Nuclear Information System (INIS)

Zhang, Zhi; Fang, Haisheng; Yan, Han; Jiang, Zhimin; Zheng, Jiang; Gan, Zhiyin

2015-01-01

Gallium nitride (GaN) is widely used in light-emitting diode (LED) devices due to its wide bandgap and excellently optoelectronic performance. The efficiency and lifetime of LEDs are critically determined by quality of GaN, for example, growth uniformity. Metal-organic chemical vapor deposition (MOCVD) is the most popular technique to grow high-quality GaN epitaxial layers. Growth uniformity is influenced by fluid flow, heat transfer and chemical reactions in the reactor. In this paper, the growth process in a close-coupled showerhead (CCS) MOCVD reactor is investigated based on 3D numerical simulation. Influences of the operating parameters on the growth uniformity are presented. To evaluate the role of the parameters systematically and efficiently on the growth uniformity, orthogonal test method is introduced. The results reveal that the growth rate and uniformity are strongly related to the total gas flow rate, the showerhead height and the inlet gas temperature, but are weakly affected by the isothermal wall temperature, the rotating speed and the susceptor temperature under the ranges of the current study. The optimized combination of the parameters is further proposed as a useful reference for obtaining the LED layers with a balance between the growth rate and the growth uniformity in industry. - Highlights: • Fluid flow, heat transfer, chemical reactions are calculated for a 3D CCS reactor. • The effects of process parameters on growth rate and uniformity are investigated. • Orthogonal test method is introduced to analyze the effect of multi-factors. • Optimal combinations can be obtained for the best growth rate and uniformity.

Wedge-Shaped GaN Nanowalls: A Potential Candidate for Two-Dimensional Electronics and Spintronics

Science.gov (United States)

Deb, Swarup; Dhar, Subhabrata

Schrödingerand Poisson equations are solved self-consistently in order to obtain the potential and charge density distribution in n-type GaN nanowalls tapered along c-axis by different angles. The study shows two-dimensional (2D) quantum confinement of electrons in the central vertical plane of the wall for the entire range of tapering. Calculation of room temperature electron mobility in the 2D channel shows a steady decrease with the increase of the inclination angle of the side facets with respect to the base. However, it is interesting to note that the mobility remains to be much larger than that of bulk GaN even for the inclination angle of 65∘. The properties of high mobility and the vertical orientation of the 2DEG plane in this system can be exploited in fabricating highly conducting transparent interconnects and field effect transistors, which can lead to large scale integration of 2D devices in future.

Direct deposition of patterned nanocrystalline CVD diamond using an electrostatic self-assembly method with nanodiamond particles

Energy Technology Data Exchange (ETDEWEB)

Lee, Seung-Koo; Kim, Jong-Hoon; Jeong, Min-Goon; Lim, Dae-Soon [Department of Materials Science and Engineering, Korea University, Anam-Dong 5-1, Seoungbuk-Ku, Seoul 136-713 (Korea, Republic of); Song, Min-Jung, E-mail: dslim@korea.ac.kr [Center for Advanced Device Materials, Korea University, Anam-Dong 5-1, Seoungbuk-Ku, Seoul 136-713 (Korea, Republic of)

2010-12-17

Micron-sized and precise patterns of nanocrystalline CVD diamond were fabricated successfully on substrates using dispersed nanodiamond particles, charge connection by electrostatic self-assembly, and photolithography processes. Nanodiamond particles which had been dispersed using an attritional milling system were attached electrostatically on substrates as nuclei for diamond growth. In this milling process, poly sodium 4-styrene sulfonate (PSS) was added as an anionic dispersion agent to produce the PSS/nanodiamond conjugates. Ultra dispersed nanodiamond particles with a {zeta}-potential and average particle size of - 60.5 mV and {approx} 15 nm, respectively, were obtained after this milling process. These PSS/nanodiamond conjugates were attached electrostatically to a cationic polyethyleneimine (PEI) coated surface on to which a photoresist had been patterned in an aqueous solution of the PSS/nanodiamond conjugated suspension. A selectively seeded area was formed successfully using the above process. A hot filament chemical vapor deposition system was used to synthesize the nanocrystalline CVD diamond on the seeded area. Micron-sized, thin and precise nanocrystalline CVD diamond patterns with a high nucleation density (3.8 {+-} 0.4 x 10{sup 11} cm{sup -2}) and smooth surface were consequently fabricated.

Direct deposition of patterned nanocrystalline CVD diamond using an electrostatic self-assembly method with nanodiamond particles

International Nuclear Information System (INIS)

Lee, Seung-Koo; Kim, Jong-Hoon; Jeong, Min-Goon; Lim, Dae-Soon; Song, Min-Jung

2010-01-01

Micron-sized and precise patterns of nanocrystalline CVD diamond were fabricated successfully on substrates using dispersed nanodiamond particles, charge connection by electrostatic self-assembly, and photolithography processes. Nanodiamond particles which had been dispersed using an attritional milling system were attached electrostatically on substrates as nuclei for diamond growth. In this milling process, poly sodium 4-styrene sulfonate (PSS) was added as an anionic dispersion agent to produce the PSS/nanodiamond conjugates. Ultra dispersed nanodiamond particles with a ζ-potential and average particle size of - 60.5 mV and ∼ 15 nm, respectively, were obtained after this milling process. These PSS/nanodiamond conjugates were attached electrostatically to a cationic polyethyleneimine (PEI) coated surface on to which a photoresist had been patterned in an aqueous solution of the PSS/nanodiamond conjugated suspension. A selectively seeded area was formed successfully using the above process. A hot filament chemical vapor deposition system was used to synthesize the nanocrystalline CVD diamond on the seeded area. Micron-sized, thin and precise nanocrystalline CVD diamond patterns with a high nucleation density (3.8 ± 0.4 x 10 11 cm -2 ) and smooth surface were consequently fabricated.

High Performance Walls in Hot-Dry Climates

Energy Technology Data Exchange (ETDEWEB)

Hoeschele, Marc [Alliance for Residential Building Innovation (ARBI), Davis, CA (United States); Springer, David [Alliance for Residential Building Innovation (ARBI), Davis, CA (United States); Dakin, Bill [Alliance for Residential Building Innovation (ARBI), Davis, CA (United States); German, Alea [Alliance for Residential Building Innovation (ARBI), Davis, CA (United States)

2015-01-01

High performance walls represent a high priority measure for moving the next generation of new homes to the Zero Net Energy performance level. The primary goal in improving wall thermal performance revolves around increasing the wall framing from 2x4 to 2x6, adding more cavity and exterior rigid insulation, achieving insulation installation criteria meeting ENERGY STAR's thermal bypass checklist. To support this activity, in 2013 the Pacific Gas & Electric Company initiated a project with Davis Energy Group (lead for the Building America team, Alliance for Residential Building Innovation) to solicit builder involvement in California to participate in field demonstrations of high performance wall systems. Builders were given incentives and design support in exchange for providing site access for construction observation, cost information, and builder survey feedback. Information from the project was designed to feed into the 2016 Title 24 process, but also to serve as an initial mechanism to engage builders in more high performance construction strategies. This Building America project utilized information collected in the California project.

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE 581 83 Linköping (Sweden)

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

Discovering a Defect that Imposes a Limit to Mg Doping in p-Type GaN

International Nuclear Information System (INIS)

Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; O'Keefe, M.A.

2006-01-01

Gallium nitride (GaN) is the III-V semiconductor used to produce blue light-emitting diodes (LEDs) and blue and ultraviolet solid-state lasers. To be useful in electronic devices, GaN must be doped with elements that function either as electron donors or as acceptors to turn it into either an n-type semiconductor or a p-type semiconductor. It has been found that GaN can easily be grown with n-conductivity, even up to large concentrations of donors--in the few 10 19 cm -3 range. However, p-doping, the doping of the structure with atoms that provide electron sinks or holes, is not well understood and remains extremely difficult. The only efficient p-type dopant is Mg, but it is found that the free hole concentration is limited to 2 x 10 18 cm -3 , even when Mg concentrations are pushed into the low 10 19 cm -3 range. This saturation effect could place a limit on further development of GaN based devices. Further increase of the Mg concentration, up to 1 x 10 20 cm -3 leads to a decrease of the free hole concentration and an increase in defects. While low- to medium-brightness GaN light-emitting diodes (LEDs) are remarkably tolerant of crystal defects, blue and UV GaN lasers are much less so. We used electron microscopy to investigate Mg doping in GaN. Our transmission electron microscopy (TEM) studies revealed the formation of different types of Mg-rich defects [1,2]. In particular, high-resolution TEM allowed us to characterize a completely new type of defect in Mg-rich GaN. We found that the type of defect depended strongly on crystal growth polarity. For crystals grown with N-polarity, planar defects are distributed at equal distances (20 unit cells of GaN); these defects can be described as inversion domains [1]. For growth with Ga-polarity, we found a different type of defect [2]. These defects turn out to be three-dimensional Mg-rich hexagonal pyramids (or trapezoids) with their base on the (0001) plane and their six walls formed on {1123} planes (Fig. 1a). In

Zn-dopant dependent defect evolution in GaN nanowires

Science.gov (United States)

Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

2015-10-01

Zn doped GaN nanowires with different doping levels (0, doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (...ABABAC&cmb.b.line;BA...) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.Zn doped GaN nanowires with different doping levels (0, doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (GaN nanowires. At high Zn doping level (3-5 at%), meta

Investigation on thermodynamics of ion-slicing of GaN and heterogeneously integrating high-quality GaN films on CMOS compatible Si(100) substrates.

Science.gov (United States)

Huang, Kai; Jia, Qi; You, Tiangui; Zhang, Runchun; Lin, Jiajie; Zhang, Shibin; Zhou, Min; Zhang, Bo; Yu, Wenjie; Ou, Xin; Wang, Xi

2017-11-08

Die-to-wafer heterogeneous integration of single-crystalline GaN film with CMOS compatible Si(100) substrate using the ion-cutting technique has been demonstrated. The thermodynamics of GaN surface blistering is in-situ investigated via a thermal-stage optical microscopy, which indicates that the large activation energy (2.5 eV) and low H ions utilization ratio (~6%) might result in the extremely high H fluence required for the ion-slicing of GaN. The crystalline quality, surface topography and the microstructure of the GaN films are characterized in detail. The full width at half maximum (FWHM) for GaN (002) X-ray rocking curves is as low as 163 arcsec, corresponding to a density of threading dislocation of 5 × 10 7  cm -2 . Different evolution of the implantation-induced damage was observed and a relationship between the damage evolution and implantation-induced damage is demonstrated. This work would be beneficial to understand the mechanism of ion-slicing of GaN and to provide a platform for the hybrid integration of GaN devices with standard Si CMOS process.

Energetics of Mg incorporation at GaN(0001) and GaN(0001¯) surfaces

Science.gov (United States)

Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

2006-04-01

By using density functional calculations in the generalized gradient approximation, we investigate the energetics of Mg adsorption and incorporation at GaN(0001) and GaN(0001¯) surfaces under various Ga and Mg coverage conditions as well as in presence of light or electron beam-induced electronic excitation. We find significant differences in Mg incorporation between Ga- and N-polar surfaces. Mg incorporation is easier at the Ga-polar surface, but high Mg coverages are found to cause important distortions which locally change the polarity from Ga to N polar. At the N-rich and moderately Ga-rich GaN(0001) surface, 0.25 ML of Mg substituting Ga in the top bilayer strongly reduce the surface diffusion barriers of Ga and N adatoms, in agreement with the surfactant effect observed in experiments. As the Mg coverage exceeds 0.5 ML, partial incorporation in the subsurface region (second bilayer) becomes favorable. A surface structure with 0.5 ML of incorporated Mg in the top bilayer and 0.25 ML in the second bilayer is found to be stable over a wide range of Ga chemical potential. At the Ga bilayer-terminated GaN(0001) surface, corresponding to Ga-rich conditions, configurations where Mg is incorporated in the interface region between the metallic Ga bilayer and the underlying GaN bilayer appear to be favored. At the N-polar surface, Mg is not incorporated under N-rich or moderately Ga-rich conditions, whereas incorporation in the adlayer may take place under Ga-rich conditions. In the presence of light or electron beam induced excitation, energy differences between Mg incorporated at the surface and in deeper layers are reduced so that the tendency toward surface segregation is also reduced.

CVD diamond windows for infrared synchrotron applications

International Nuclear Information System (INIS)

Sussmann, R.S.; Pickles, C.S.J.; Brandon, J.R.; Wort, C.J.H.; Coe, S.E.; Wasenczuk, A.; Dodge, C.N.; Beale, A.C.; Krehan, A.J.; Dore, P.; Nucara, A.; Calvani, P.

1998-01-01

This paper describes the attributes that make diamond a unique material for infrared synchrotron beam experiments. New developments in diamond synthesised by Chemical Vapour Deposition (CVD) promise to extend the range of applications which have been hitherto limited by the availability and cost of large-size single-crystal diamond. Polycrystalline CVD diamond components such as large (100 mm) diameter windows with extremely good transparency over a wide spectral range are now commercially available. Properties of CVD diamond of relevance to optical applications, such as mechanical strength, thermal conductivity and absolute bulk absorption, are discussed. It is shown that although some of the properties of CVD diamond (similar to other polycrystalline industrial ceramics) are affected by the grain structure, currently produced CVD diamond optical components have the quality and performance required for numerous demanding applications

GaN transistors for efficient power conversion

CERN Document Server

Lidow, Alex; de Rooij, Michael; Reusch, David

2014-01-01

The first edition of GaN Transistors for Efficient Power Conversion was self-published by EPC in 2012, and is currently the only other book to discuss GaN transistor technology and specific applications for the technology. More than 1,200 copies of the first edition have been sold through Amazon or distributed to selected university professors, students and potential customers, and a simplified Chinese translation is also available. The second edition has expanded emphasis on applications for GaN transistors and design considerations. This textbook provides technical and application-focused i

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation

International Nuclear Information System (INIS)

Hwang, Jih-Shang; Liu, Tai-Yan; Chen, Han-Wei; Chattopadhyay, Surjit; Hsu, Geng-Ming; Basilio, Antonio M; Hsu, Yu-Kuei; Tu, Wen-Hsun; Lin, Yan-Gu; Chen, Kuei-Hsien; Li, Chien-Cheng; Wang, Sheng-Bo; Chen, Hsin-Yi; Chen, Li-Chyong

2013-01-01

Enhanced photoelectrochemical (PEC) performances of Ga 2 O 3 and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga 2 O 3 and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga 2 O 3 NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga 2 O 3 . These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga 2 O 3 NWs, or by incorporation of indium to form InGaN NWs. (paper)

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation.

Science.gov (United States)

Hwang, Jih-Shang; Liu, Tai-Yan; Chattopadhyay, Surjit; Hsu, Geng-Ming; Basilio, Antonio M; Chen, Han-Wei; Hsu, Yu-Kuei; Tu, Wen-Hsun; Lin, Yan-Gu; Chen, Kuei-Hsien; Li, Chien-Cheng; Wang, Sheng-Bo; Chen, Hsin-Yi; Chen, Li-Chyong

2013-02-08

Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.

Numerical study of natural melt convection in cylindrical cavity with hot walls and cold bottom sink

Directory of Open Access Journals (Sweden)

Ahmanache Abdennacer

2013-01-01

Full Text Available Numerical study of natural convection heat transfer and fluid flow in cylindrical cavity with hot walls and cold sink is conducted. Calculations are performed in terms of the cavity aspect ratio, the heat exchanger length and the thermo physical properties expressed via the Prandtl number and the Rayleigh number. Results are presented in the form of isotherms, streamlines, average Nusselt number and average bulk temperature for a range of Rayleigh number up to 106. It is observed that Rayleigh number and heat exchanger length influences fluid flow and heat transfer, whereas the cavity aspect ratio has no significant effects.

Post-annealing effects on pulsed laser deposition-grown GaN thin films

International Nuclear Information System (INIS)

Cheng, Yu-Wen; Wu, Hao-Yu; Lin, Yu-Zhong; Lee, Cheng-Che; Lin, Ching-Fuh

2015-01-01

In this work, the post-annealing effects on gallium nitride (GaN) thin films grown from pulsed laser deposition (PLD) are investigated. The as-deposited GaN thin films grown from PLD are annealed at different temperatures in nitrogen ambient. Significant changes of the GaN crystal properties are observed. Raman spectroscopy is used to observe the crystallinity, the change of residual stress, and the thermal decomposition of the annealed GaN thin films. X-ray diffraction is also applied to identify the crystal phase of GaN thin films, and the surface morphology of GaN thin films annealed at different temperatures is observed by scanning electron microscopy. Through the above analyses, the GaN thin films grown by PLD undergo three stages: phase transition, stress alteration, and thermal decomposition. At a low annealing temperature, the rock salt GaN in GaN films is transformed into wurtzite. The rock salt GaN diminishes with increasing annealing temperature. At a medium annealing temperature, the residual stress of the film changes significantly from compressive strain to tensile strain. As the annealing temperature further increases, the GaN undergoes thermal decomposition and the surface becomes granular. By investigating the annealing temperature effects and controlling the optimized annealing temperature of the GaN thin films, we are able to obtain highly crystalline and strain-free GaN thin films by PLD. - Highlights: • The GaN thin film is grown on sapphire by pulsed laser deposition. • The GaN film undergoes three stages with increasing annealing temperature. • In the first stage, the film transfers from rock salt to wurtzite phase. • In the second stage, the stress in film changes from compressive to tensile. • In the final stage, the film thermally decomposes and becomes granular

Alignment control and atomically-scaled heteroepitaxial interface study of GaN nanowires.

Science.gov (United States)

Liu, Qingyun; Liu, Baodan; Yang, Wenjin; Yang, Bing; Zhang, Xinglai; Labbé, Christophe; Portier, Xavier; An, Vladimir; Jiang, Xin

2017-04-20

Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH 3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001) GaN ∥(0001) sapphire and (101[combining macron]0) GaN ∥(112[combining macron]0) sapphire . Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

CVD diamond deposition onto dental burs

International Nuclear Information System (INIS)

Ali, N.; Sein, H.

2001-01-01

A hot-filament chemical vapor deposition (HFCVD) system has been modified to enable non-planar substrates, such as metallic wires and dental burs, to be uniformly coated with thin polycrystalline diamond films. Initially, diamond deposition was carried out on titanium and tantalum wires in order to test and optimize the system. High growth rates of the order of approx. 8 /hr were obtained when depositing diamond on titanium wires using the vertical filament arrangement. However, lower growth rates of the order of 4-5meu m/hr were obtained with diamond deposition on tantalum wires. To extend the work towards a practical biomedical application tungsten carbide dental burs were coated with diamond films. The as-grown films were found to be polycrystalline and uniform over the cutting tip. Finally, the costs relating to diamond CVD onto dental burs have been presented in this paper. The costs relating to coating different number of burs at a time and the effect of film thickness on costs have been included in this investigation. (author)

StackGAN++: Realistic Image Synthesis with Stacked Generative Adversarial Networks

OpenAIRE

Zhang, Han; Xu, Tao; Li, Hongsheng; Zhang, Shaoting; Wang, Xiaogang; Huang, Xiaolei; Metaxas, Dimitris

2017-01-01

Although Generative Adversarial Networks (GANs) have shown remarkable success in various tasks, they still face challenges in generating high quality images. In this paper, we propose Stacked Generative Adversarial Networks (StackGAN) aiming at generating high-resolution photo-realistic images. First, we propose a two-stage generative adversarial network architecture, StackGAN-v1, for text-to-image synthesis. The Stage-I GAN sketches the primitive shape and colors of the object based on given...

Ab initio investigations of the strontium gallium nitride ternaries Sr 3GaN3 and Sr6GaN5: Promising materials for optoelectronic

KAUST Repository

Goumri-Said, Souraya

2013-05-31

Sr3GaN3 and Sr6GaN5 could be promising potential materials for applications in the microelectronics, optoelectronics and coating materials areas of research. We studied in detail their structural, elastic, electronic, optical as well as the vibrational properties, by means of density functional theory framework. Both of these ternaries are semiconductors, where Sr3GaN3 exhibits a small indirect gap whereas Sr6GaN5 has a large direct gap. Indeed, their optical properties are reported for radiation up to 40 eV. Charge densities contours, Hirshfeld and Mulliken populations, are reported to investigate the role of each element in the bonding. From the mechanical properties calculation, it is found that Sr6GaN5 is harder than Sr3GaN3, and the latter is more anisotropic than the former. The phonon dispersion relation, density of phonon states and the vibrational stability are reported from the density functional perturbation theory calculations. © 2013 IOP Publishing Ltd.

Lattice-Symmetry-Driven Epitaxy of Hierarchical GaN Nanotripods

KAUST Repository

Wang, Ping

2017-01-18

Lattice-symmetry-driven epitaxy of hierarchical GaN nanotripods is demonstrated. The nanotripods emerge on the top of hexagonal GaN nanowires, which are selectively grown on pillar-patterned GaN templates using molecular beam epitaxy. High-resolution transmission electron microscopy confirms that two kinds of lattice-symmetry, wurtzite (wz) and zinc-blende (zb), coexist in the GaN nanotripods. Periodical transformation between wz and zb drives the epitaxy of the hierarchical nanotripods with N-polarity. The zb-GaN is formed by the poor diffusion of adatoms, and it can be suppressed by improving the ability of the Ga adatoms to migrate as the growth temperature increased. This controllable epitaxy of hierarchical GaN nanotripods allows quantum dots to be located at the phase junctions of the nanotripods and nanowires, suggesting a new recipe for multichannel quantum devices.

CVD Diamond Detectors for Current Mode Neutron Time-of-Flight Spectroscopy at OMEGA/NIF

International Nuclear Information System (INIS)

G. J. Schmid; V. Yu. Glebov; A. V. Friensehner; D. R. Hargrove; S. P. Hatchett; N. Izumi; R. A. Lerche; T. W. Phillips; T. C. Sangster; C. Silbernagel; C. Stoecki

2001-01-01

We have performed pulsed neutron and pulsed laser tests of a CVD diamond detector manufactured from DIAFILM, a commercial grade of CVD diamond. The laser tests were performed at the short pulse UV laser at Bechtel Nevada in Livermore, CA. The pulsed neutrons were provided by DT capsule implosions at the OMEGA laser fusion facility in Rochester, NY. From these tests, we have determined the impulse response to be 250 ps fwhm for an applied E-field of 500 V/mm. Additionally, we have determined the sensitivity to be 2.4 mA/W at 500 V/mm and 4.0 mA/W at 1000 V/mm. These values are approximately 2 to 5x times higher than those reported for natural Type IIa diamond at similar E-field and thickness (1mm). These characteristics allow us to conceive of a neutron time-of-flight current mode spectrometer based on CVD diamond. Such an instrument would sit inside the laser fusion target chamber close to target chamber center (TCC), and would record neutron spectra fast enough such that backscattered neutrons and x-rays from the target chamber wall would not be a concern. The acquired neutron spectra could then be used to extract DD fuel areal density from the downscattered secondary to secondary ratio

GaN and ZnO nanostructures

Energy Technology Data Exchange (ETDEWEB)

Fuendling, Soenke; Soekmen, Uensal; Behrends, Arne; Al-Suleiman, Mohamed Aid Mansur; Merzsch, Stephan; Li, Shunfeng; Bakin, Andrey; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, Technische Universitaet Braunschweig, Braunschweig (Germany); Laehnemann, Jonas; Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

2010-10-15

GaN and ZnO are both wide band gap semiconductors with interesting properties concerning optoelectronic and sensor device applications. Due to the lack or the high costs of native substrates, alternatives like sapphire, silicon, or silicon carbide are taken, but the resulting lattice and thermal mismatches lead to increased defect densities which reduce the material quality. In contrast, nanostructures with high aspect ratio have lower defect densities as compared to layers. In this work, we give an overview on our results achieved on both ZnO as well as GaN based nanorods. ZnO nanostructures were grown by a wet chemical approach as well as by VPT on different substrates - even on flexible polymers. To compare the growth results we analyzed the structures by XRD and PL and show possible device applications. The GaN nano- and microstructures were grown by metal organic vapor phase epitaxy either in a self-organized process or by selective area growth for a better control of shape and material composition. Finally we take a look onto possible device applications, presenting our attempts, e.g., to build LEDs based on GaN nanostructures. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Gallium adsorption on (0001) GaN surfaces

International Nuclear Information System (INIS)

Adelmann, Christoph; Brault, Julien; Mula, Guido; Daudin, Bruno; Lymperakis, Liverios; Neugebauer, Joerg

2003-01-01

We study the adsorption behavior of Ga on (0001) GaN surfaces combining experimental specular reflection high-energy electron diffraction with theoretical investigations in the framework of a kinetic model for adsorption and ab initio calculations of energy parameters. Based on the experimental results we find that for substrate temperatures and Ga fluxes typically used in molecular-beam epitaxy of GaN, finite equilibrium Ga surface coverages can be obtained. The measurement of a Ga/GaN adsorption isotherm allows the quantification of the equilibrium Ga surface coverage as a function of the impinging Ga flux. In particular, we show that a large range of Ga fluxes exists, where 2.5±0.2 monolayers (in terms of the GaN surface site density) of Ga are adsorbed on the GaN surface. We further demonstrate that the structure of this adsorbed Ga film is in good agreement with the laterally contracted Ga bilayer model predicted to be most stable for strongly Ga-rich surfaces [Northrup et al., Phys. Rev. B 61, 9932 (2000)]. For lower Ga fluxes, a discontinuous transition to Ga monolayer equilibrium coverage is found, followed by a continuous decrease towards zero coverage; for higher Ga fluxes, Ga droplet formation is found, similar to what has been observed during Ga-rich GaN growth. The boundary fluxes limiting the region of 2.5 monolayers equilibrium Ga adsorption have been measured as a function of the GaN substrate temperature giving rise to a Ga/GaN adsorption phase diagram. The temperature dependence is discussed within an ab initio based growth model for adsorption taking into account the nucleation of Ga clusters. This model consistently explains recent contradictory results of the activation energy describing the critical Ga flux for the onset of Ga droplet formation during Ga-rich GaN growth [Heying et al., J. Appl. Phys. 88, 1855 (2000); Adelmann et al., J. Appl. Phys. 91, 9638 (2002).

Fermented dairy food and CVD risk.

Science.gov (United States)

Tapsell, Linda C

2015-04-01

Fermented dairy foods such as yoghurt and cheese are commonly found in the Mediterranean diet. Recent landmark research has confirmed the effect of the Mediterranean diet on reducing the CVD risk, but the relative contributions of fermented dairy foods have not been fully articulated. The present study provides a review of the relationship between fermented dairy foods consumption and CVD risk in the context of the whole diet. Studies show that people who eat healthier diets may be more likely to consume yoghurt, so there is a challenge in attributing separate effects to yoghurt. Analyses from large population studies list yoghurt as the food most negatively associated with the risk of weight gain (a problem that may lead to CVD). There is some suggestion that fermented dairy foods consumption (yoghurt or cheese) may be associated with reduced inflammatory biomarkers associated with the development of CVD. Dietary trials suggest that cheese may not have the same effect on raising LDL-cholesterol levels as butter with the same saturated fat content. The same might be stated for yoghurt. The use of different probiotic cultures and other aspects of study design remain a problem for research. Nevertheless, population studies from a range of countries have shown that a reduced risk of CVD occurs with the consumption of fermented dairy foods. A combination of evidence is necessary, and more research is always valuable, but indications remain that fermented dairy foods such as cheese and yoghurt are integral to diets that are protective against CVD.

Synthesis of GaN Nanorods by a Solid-State Reaction

Directory of Open Access Journals (Sweden)

Keyan Bao

2010-01-01

Full Text Available An atom-economical and eco-friendly chemical synthetic route was developed to synthesize wurtzite GaN nanorods by the reaction of NaNH2 and the as-synthesized orthorhombic GaOOH nanorods in a stainless steel autoclave at 600∘C. The lengths of the GaN nanorods are in the range of 400–600 nm and the diameters are about 80–150 nm. The process of orthorhombic GaOOH nanorods transformation into wurtzite GaN nanorods was investigated by powder X-ray diffraction (XRD and field emission scanning electron microscope (FESEM, indicating that the GaN product retained essentially the same basic topological morphology in contrast to that of the GaOOH precursor. It was found that rhombohedral Ga2O3 was the intermediate between the starting orthorhombic GaOOH precursor and the final wurtzite GaN product. The photoluminescence measurements reveal that the as-prepared wurtzite GaN nanorods showed strong blue emission.

GaN Nanowires Synthesized by Electroless Etching Method

KAUST Repository

Najar, Adel; Anjum, Dalaver H.; Ng, Tien Khee; Ooi, Boon S.; Ben Slimane, Ahmed

2012-01-01

Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

Structural analysis of GaN using high-resolution X-ray diffraction at variable temperatures; Analyse struktureller Eigenschaften von GaN mittels hochaufloesender Roentgenbeugung bei variabler Messtemperatur

Energy Technology Data Exchange (ETDEWEB)

Roder, C.

2007-02-26

The main topic of this thesis was the study of stress phenomena in GaN layers by application of high-resolution X-ray diffractometry at variable measurement temperature. For this a broad spectrum of different GaN samples was studied, which extended from bulk GaN crystals as well as thick c-plane oriented HVPE-GaN layers on c-plane sapphire over laterlaly overgrown c-plane GaN Layers on Si(111) substrates toon-polar a-plnae GaN layers on r-plane sapphire. The main topic of the measurements was the determination of the lattice parameters. Supplementarily the curvature of the waver as well as the excitonic resosance energies were studied by means of photoluminescence respectively photoreflection spectroscopy. By the measurement of the temperature-dependent lattice parameters of different GaN bulk crystals for the first time a closed set of thermal-expansion coefficients of GaN was determined from 12 to 1205 K with large accuracy. Analoguously the thermal-expansion coefficents of the substrate material sapphire were determinde over a temperature range from 10 to 1166 K.

Hole-induced d"0 ferromagnetism enhanced by Na-doping in GaN

International Nuclear Information System (INIS)

Zhang, Yong; Li, Feng

2017-01-01

The d"0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature. - Highlights: • Hole-induced ferromagnetism in GaN is confirmed. • Both Ga Vacancy and Na-doping can introduce hole into GaN. • The concentration of Ga vacancy is too low to induce detectable ferromagnetism. • Na-doped GaN is a possible ferromagnet with a high curie-temperature.

Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles.

Science.gov (United States)

Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel; Hilfiker, Andres

2016-01-01

Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle-cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

Optical properties of Mg doped p-type GaN nanowires

Science.gov (United States)

Patsha, Avinash; Pandian, Ramanathaswamy; Dhara, S.; Tyagi, A. K.

2015-06-01

Mg doped p-type GaN nanowires are grown using chemical vapor deposition technique in vapor-liquid-solid (VLS) process. Morphological and structural studies confirm the VLS growth process of nanowires and wurtzite phase of GaN. We report the optical properties of Mg doped p-type GaN nanowires. Low temperature photoluminescence studies on as-grown and post-growth annealed samples reveal the successful incorporation of Mg dopants. The as-grwon and annealed samples show passivation and activation of Mg dopants, respectively, in GaN nanowires.

Elastic scattering by hot electrons and apparent lifetime of longitudinal optical phonons in gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Khurgin, Jacob B., E-mail: jakek@jhu.edu [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Bajaj, Sanyam; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

2015-12-28

Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results.

Molecularly ordered aluminum tris-(8-hydroxyquinoline) thin films grown by hot-wall deposition

Energy Technology Data Exchange (ETDEWEB)

Tapponnier, A. [Nonlinear Optics Laboratory, Institute of Quantum Electronics, Swiss Federal Institute of Technology Zuerich (ETH), CH-8093 Zurich (Switzerland)]. E-mail: axelle@phys.ethz.ch; Khan, R.U.A. [Nonlinear Optics Laboratory, Institute of Quantum Electronics, Swiss Federal Institute of Technology Zuerich (ETH), CH-8093 Zurich (Switzerland); Marcolli, C. [Institute of Atmospheric and Climate Sciences, Swiss Federal Institute of Technology Zuerich (ETH), CH-8092 Zurich (Switzerland); Guenter, P. [Nonlinear Optics Laboratory, Institute of Quantum Electronics, Swiss Federal Institute of Technology Zuerich (ETH), CH-8093 Zurich (Switzerland)

2007-01-22

We report on the growth and microstructural analysis of molecularly ordered thin film layers of aluminum tris-(8-hydroxyquinoline) (Alq{sub 3}) by hot-wall deposition onto amorphous glass substrates. Using transmission electron microscopy (TEM), ordering on a scale of 100 nm was observed. Raman measurements of these films indicated that they corresponded to the {alpha}-polymorph of crystalline Alq{sub 3}, and photoluminescence measurements exhibited a single broad peak centered at 500 nm, which is also consistent with the {alpha}-form. As a comparison, we deposited films of Alq3 using organic molecular beam deposition (OMBD), which exhibited no molecular ordering from the TEM studies. For these films, strong point-to-point variations in the Raman spectrum, and the existence of a double peak in the photoluminescence at 500 and 522 nm were observed. These measurements indicate that the OMBD films possess a mixture of both {alpha} and amorphous phases.

The role of the substrate surface morphology and water in growth of vertically aligned single-walled carbon nanotubes.

Science.gov (United States)

Pint, Cary; Pheasant, Sean; Nicholas, Nolan; Horton, Charles; Hauge, Robert

2008-11-01

Growth of high quality, vertically aligned single-walled carbon nanotubes (carpets) is achieved using a rapid insertion hot filament chemical vapor deposition (HF-CVD) technique. The effect of the substrate morphology on growth is explored by comparing carpets grown on epitaxially polished MgO substrates to those grown on "as-cut", macroscopically rough MgO substrates. Depending on the substrate morphology, we observe differences in both the overall carpet morphology as well as the diameter distribution of nanotubes grown in the carpet based on optical measurements. In addition, we explore the role of water in the growth of carpets on MgO and the conventional Al2O3 coated Si substrates. We find that the addition of a small amount of water is beneficial to the growth rates of the SWNT carpets, enhancing the growth rates by up to eight times.

Electronic Transport Mechanism for Schottky Diodes Formed by Au/HVPE a-Plane GaN Templates Grown via In Situ GaN Nanodot Formation

Directory of Open Access Journals (Sweden)

Moonsang Lee

2018-06-01

Full Text Available We investigate the electrical characteristics of Schottky contacts for an Au/hydride vapor phase epitaxy (HVPE a-plane GaN template grown via in situ GaN nanodot formation. Although the Schottky diodes present excellent rectifying characteristics, their Schottky barrier height and ideality factor are highly dependent upon temperature variation. The relationship between the barrier height, ideality factor, and conventional Richardson plot reveals that the Schottky diodes exhibit an inhomogeneous barrier height, attributed to the interface states between the metal and a-plane GaN film and to point defects within the a-plane GaN layers grown via in situ nanodot formation. Also, we confirm that the current transport mechanism of HVPE a-plane GaN Schottky diodes grown via in situ nanodot formation prefers a thermionic field emission model rather than a thermionic emission (TE one, implying that Poole–Frenkel emission dominates the conduction mechanism over the entire range of measured temperatures. The deep-level transient spectroscopy (DLTS results prove the presence of noninteracting point-defect-assisted tunneling, which plays an important role in the transport mechanism. These electrical characteristics indicate that this method possesses a great throughput advantage for various applications, compared with Schottky contact to a-plane GaN grown using other methods. We expect that HVPE a-plane GaN Schottky diodes supported by in situ nanodot formation will open further opportunities for the development of nonpolar GaN-based high-performance devices.

MgO by injection CVD

International Nuclear Information System (INIS)

Abrutis, A.; Kubilius, V.; Teiserkis, A.; Bigelyte, V.; Vengalis, B.; Jukna, A.; Butkute, R.

1997-01-01

Epitaxial YBa 2 Cu 3 O 7 layers with 45 in-plane orientation have been grown by injection CVD on MgO substrates polished off-axis to within 1.4-1.9 of the [100] direction. This new single-source CVD process is based on computer-controlled injection of precise microdoses of a metal-organic precursor solution into a CVD reactor. A wide range of solution compositions was tested to investigate compositional effects on phase purity, surface morphology, texturing and superconducting properties of the prepared films. The highest quality films with pure 45 texture had a smooth surface, zero resistance T c (R=0) of 88-89 K, and critical current density J c (77 K) above 10 6 A/cm 2 . (orig.) and critical current density J c (77 K) above 10 6 A/cm 2 . (orig.)

Growth of GaN micro/nanolaser arrays by chemical vapor deposition.

Science.gov (United States)

Liu, Haitao; Zhang, Hanlu; Dong, Lin; Zhang, Yingjiu; Pan, Caofeng

2016-09-02

Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry-Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c-GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ∼1 μm and a length of ∼15 μm. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry-Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm(-2). The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices.

Plasma-wall interaction

International Nuclear Information System (INIS)

Reichle, R.

2004-01-01

This document gathers the 43 slides presented in the framework of the week long lecture 'hot plasmas 2004' and dedicated to plasma-wall interaction in a tokamak. This document is divided into 4 parts: 1) thermal load on the wall, power extraction and particle recovery, 2) basic edge plasma physics, 3) processes that drive the plasma-solid interaction, and 4) material conditioning (surface treatment...) for ITER

High surface hole concentration p-type GaN using Mg implantation

International Nuclear Information System (INIS)

Long Tao; Yang Zhijian; Zhang Guoyi

2001-01-01

Mg ions were implanted on Mg-doped GaN grown by metalorganic chemical vapor deposition (MOCVD). The p-type GaN was achieved with high hole concentration (8.28 x 10 17 cm -3 ) conformed by Van derpauw Hall measurement after annealing at 800 degree C for 1 h. this is the first experimental report of Mg implantation on Mg-doped GaN and achieving p-type GaN with high surface hole concentration

Jumping-droplet electronics hot-spot cooling

Science.gov (United States)

Oh, Junho; Birbarah, Patrick; Foulkes, Thomas; Yin, Sabrina L.; Rentauskas, Michelle; Neely, Jason; Pilawa-Podgurski, Robert C. N.; Miljkovic, Nenad

2017-03-01

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm × 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobic surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22-25 °C air temperature, 20%-45% relative humidity) to determine the effect of gap spacing (2-4 mm), electric field (50-250 V/cm) and applied heat flux (demonstrated to 13 W/cm2). EFE condensation was shown to enhance the heat transfer from the local hot spot by ≈200% compared to cooling without jumping and by 20% compared to non-EFE jumping. Dynamic switching of the electric field for a two-GaN system reveals the potential for active cooling of mobile hot spots. The opportunity for further cooling enhancement by the removal of non-condensable gases promises hot spot heat dissipation rates approaching 120 W/cm2. This work provides a framework for the development of active jumping droplet based vapor chambers and heat pipes capable of spatial and temporal thermal dissipation control.

Jumping-droplet electronics hot-spot cooling

International Nuclear Information System (INIS)

Oh, Junho; Birbarah, Patrick; Foulkes, Thomas; Yin, Sabrina L.; Rentauskas, Michelle

2017-01-01

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm x 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobic surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22-25°C air temperature, 20-45% relative humidity) to determine the effect of gap spacing (2-4 mm), electric field (50-250 V/cm), and heat flux (demonstrated to 13 W/cm"2). EFE condensation was shown to enhance the heat transfer from the local hot spot by ≈ 200% compared to cooling without jumping and by 20% compared to non-EFE jumping. Dynamic switching of the electric field for a two-GaN system reveals the potential for active cooling of mobile hot spots. The opportunity for further cooling enhancement by the removal of non-condensable gases promises hot spot heat dissipation rates approaching 120 W/cm"2. Finally, this work provides a framework for the development of active jumping droplet based vapor chambers and heat pipes capable of spatial and temporal thermal dissipation control.

Semipolar GaN grown on m-plane sapphire using MOVPE

Energy Technology Data Exchange (ETDEWEB)

Wernicke, Tim; Netzel, Carsten; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany); Kneissl, Michael [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany); Institute of Solid State Physics, Technical University of Berlin (Germany)

2008-07-01

We have investigated the MOVPE growth of semipolar gallium nitride (GaN) films on (10 anti 1 0) m-plane sapphire substrates. Specular GaN films with a RMS roughness (10 x 10 {mu}m{sup 2}) of 15.2 nm were obtained and an arrowhead like structure aligned along[ anti 2 113] is prevailing. The orientation relationship was determined by XRD and yielded (212){sub GaN} parallel (10 anti 10){sub sapphire} and [anti 2113]{sub GaN} parallel [0001]{sub sapphire} as well as [anti 2113]{sub GaN} parallel [000 anti 1]{sub sapphire}. PL spectra exhibited near band edge emission accompanied by a strong basal plane stacking fault emission. In addition lower energy peaks attributed to prismatic plane stacking faults and donor acceptor pair emission appeared in the spectrum. With similar growth conditions also (1013) GaN films on m-plane sapphire were obtained. In the later case we found that the layer was twinned, crystallites with different c-axis orientation were present. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Preparation of freestanding GaN wafer by hydride vapor phase epitaxy on porous silicon

Science.gov (United States)

Wu, Xian; Li, Peng; Liang, Renrong; Xiao, Lei; Xu, Jun; Wang, Jing

2018-05-01

A freestanding GaN wafer was prepared on porous Si (111) substrate using hydride vapor phase epitaxy (HVPE). To avoid undesirable effects of the porous surface on the crystallinity of the GaN, a GaN seed layer was first grown on the Si (111) bare wafer. A pattern with many apertures was fabricated in the GaN seed layer using lithography and etching processes. A porous layer was formed in the Si substrate immediately adjacent to the GaN seed layer by an anodic etching process. A 500-μm-thick GaN film was then grown on the patterned GaN seed layer using HVPE. The GaN film was separated from the Si substrate through the formation of cracks in the porous layer caused by thermal mismatch stress during the cooling stage of the HVPE. Finally, the GaN film was polished to obtain a freestanding GaN wafer.

Identification of deep levels in GaN associated with dislocations

International Nuclear Information System (INIS)

Soh, C B; Chua, S J; Lim, H F; Chi, D Z; Liu, W; Tripathy, S

2004-01-01

To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-doped GaN and cracked AlGaN templates are also chosen for this study. The purpose of growth of such continuous GaN layers on top of the cracked templates is to reduce the screw dislocation density by an order of magnitude. Deep levels in these layers have been characterized and compared with emphasis on their thermal stabilities and capture kinetics. Three electron traps at E c -E T ∼0.10-0.11, 0.24-0.27 and 0.59-0.63 eV are detected common to all the samples while additional levels at E c -E T ∼0.18 and 0.37-0.40 eV are also observed in the Si-doped GaN. The trap levels exhibit considerably different stabilities under rapid thermal annealing. Based on the observations, the trap levels at E c -E T ∼0.18 and 0.24-0.27 eV can be associated with screw dislocations, whereas the level at E c -E T ∼0.59-0.63 eV can be associated with edge dislocations. This is also in agreement with the transmission electron microscopy measurements conducted on the GaN samples

High-quality GaN epitaxially grown on Si substrate with serpentine channels

Science.gov (United States)

Wei, Tiantian; Zong, Hua; Jiang, Shengxiang; Yang, Yue; Liao, Hui; Xie, Yahong; Wang, Wenjie; Li, Junze; Tang, Jun; Hu, Xiaodong

2018-06-01

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 × 107 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.

Characteristics of wall pressure over wall with permeable coating

Energy Technology Data Exchange (ETDEWEB)

Song, Woo Seog; Shin, Seungyeol; Lee, Seungbae [Inha Univ., Incheon (Korea, Republic of)

2012-11-15

Fluctuating wall pressures were measured using an array of 16 piezoelectric transducers beneath a turbulent boundary layer. The coating used in this experiment was an open cell, urethane type foam with a porosity of approximately 50 ppi. The ultimate objective of the coating is to provide a mechanical filter to reduce the wall pressure fluctuations. The ultimate objective of the coating is to provide a mechanical filter to reduce the wall pressure fluctuations. The boundary layer on the flat plate was measured by using a hot wire probe, and the CPM method was used to determine the skin friction coefficient. The wall pressure autospectra and streamwise wavenumber frequency spectra were compared to assess the attenuation of the wall pressure field by the coating. The coating is shown to attenuate the convective wall pressure energy. However, the relatively rough surface of the coating in this investigation resulted in a higher mean wall shear stress, thicker boundary layer, and higher low frequency wall pressure spectral levels compared to a smooth wall.

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

Science.gov (United States)

Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-01-01

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

Directory of Open Access Journals (Sweden)

Hongbo Qin

2017-12-01

Full Text Available For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100 and (111 are isotropic, while the Poisson’s ratio at plane (110 exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals.

Science.gov (United States)

Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-12-12

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol -1 K -1 , respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of

High surface hole concentration p-type GaN using Mg implantation

CERN Document Server

Long Tao; Zhang Guo Yi

2001-01-01

Mg ions were implanted on Mg-doped GaN grown by metalorganic chemical vapor deposition (MOCVD). The p-type GaN was achieved with high hole concentration (8.28 x 10 sup 1 sup 7 cm sup - sup 3) conformed by Van derpauw Hall measurement after annealing at 800 degree C for 1 h. this is the first experimental report of Mg implantation on Mg-doped GaN and achieving p-type GaN with high surface hole concentration

The 2018 GaN power electronics roadmap

Science.gov (United States)

Amano, H.; Baines, Y.; Beam, E.; Borga, Matteo; Bouchet, T.; Chalker, Paul R.; Charles, M.; Chen, Kevin J.; Chowdhury, Nadim; Chu, Rongming; De Santi, Carlo; Merlyne De Souza, Maria; Decoutere, Stefaan; Di Cioccio, L.; Eckardt, Bernd; Egawa, Takashi; Fay, P.; Freedsman, Joseph J.; Guido, L.; Häberlen, Oliver; Haynes, Geoff; Heckel, Thomas; Hemakumara, Dilini; Houston, Peter; Hu, Jie; Hua, Mengyuan; Huang, Qingyun; Huang, Alex; Jiang, Sheng; Kawai, H.; Kinzer, Dan; Kuball, Martin; Kumar, Ashwani; Boon Lee, Kean; Li, Xu; Marcon, Denis; März, Martin; McCarthy, R.; Meneghesso, Gaudenzio; Meneghini, Matteo; Morvan, E.; Nakajima, A.; Narayanan, E. M. S.; Oliver, Stephen; Palacios, Tomás; Piedra, Daniel; Plissonnier, M.; Reddy, R.; Sun, Min; Thayne, Iain; Torres, A.; Trivellin, Nicola; Unni, V.; Uren, Michael J.; Van Hove, Marleen; Wallis, David J.; Wang, J.; Xie, J.; Yagi, S.; Yang, Shu; Youtsey, C.; Yu, Ruiyang; Zanoni, Enrico; Zeltner, Stefan; Zhang, Yuhao

2018-04-01

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

Understanding the Room Temperature Ferromagnetism in GaN Nanowires with Pd Doping

International Nuclear Information System (INIS)

Manna, S; De, S K

2011-01-01

We report the first synthesis and characterization of 4d transition metal palladium-doped GaN nanowires (NWs). Room temperature ferromagnetism has been observed in high quality Vapor Liquid Solid (VLS) epitaxy grown undoped n-type GaN nanowires. It was proposed that this type of magnetism is due to defects which are not observed in Bulk GaN because of large formation energy of defects in bulk GaN. Here we have successfully doped 4d transition metal Pd in GaN NWs. We find fairly strong and long-range ferromagnetic coupling between Pd substituted for Ga in GaN . The results suggest that 4d metals such as Pd may also be considered as candidates for ferromagnetic dopants in semiconductors.

TEM characterization of catalyst- and mask-free grown GaN nanorods

International Nuclear Information System (INIS)

Schowalter, M; Aschenbrenner, T; Kruse, C; Hommel, D; Rosenauer, A

2010-01-01

Catalyst- and mask-free grown GaN nanorods have been investigated using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy filtered transmission electron microscopy (EFTEM). The nanorods were grown on nitridated r-plane sapphire substrates in a molecular beam epitaxy reactor. We investigated samples directly after the nitridation and after the overgrowth of the structure with GaN. High resolution transmission electron microscopy (HRTEM) and EFTEM revealed that AlN islands have formed due to nitridation. After overgrowth, the AlN islands could not be observed any more, neither by EFTEM nor by Z-contrast imaging. Instead, a smooth layer consisting of AlGaN was found. The investigation of the overgrown sample revealed that an a-plane GaN layer and GaN nanorods on top of the a-plane GaN have formed. The nanorods reduced from top of the a-plane GaN towards the a-plane GaN/sapphire interface suggesting that the nanorods originate at the AlN islands found after nitridation. However, this could not be shown unambiguously. The number of threading dislocations in the nanorods was very low. The analysis of the epitaxial relationship to the a-plane GaN showed that the nanorods grew along the [000-1] direction, and the [1-100] direction of the rods was parallel to the [0001] direction of the a-plane GaN.

New developments in CVD diamond for detector applications

Science.gov (United States)

Adam, W.; Berdermann, E.; Bergonzo, P.; de Boer, W.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Dulinski, W.; Doroshenko, J.; van Eijk, B.; Fallou, A.; Fischer, P.; Fizzotti, F.; Furetta, C.; Gan, K. K.; Ghodbane, N.; Grigoriev, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kaplon, J.; Kass, R.; Keil, M.; Knoepfle, K. T.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D.; Menichelli, D.; Meuser, S.; Mishina, M.; Moroni, L.; Noomen, J.; Oh, A.; Pernicka, M.; Perera, L.; Potenza, R.; Riester, J. L.; Roe, S.; Rudge, A.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Sutera, C.; Trischuk, W.; Tromson, D.; Tuve, C.; Vincenzo, B.; Weilhammer, P.; Wermes, N.; Wetstein, M.; Zeuner, W.; Zoeller, M.

Chemical Vapor Deposition (CVD) diamond has been discussed extensively as an alternative sensor material for use very close to the interaction region of the LHC and other machines where extreme radiation conditions exist. During the last seven years the RD42 collaboration has developed diamond detectors and tested them with LHC electronics towards the end of creating a device usable by experiments. The most recent results of this work are presented. Recently, a new form of CVD diamond has been developed: single crystal CVD diamond which resolves many of the issues associated with poly-crystalline CVD material. The first tests of this material are also presented.

New developments in CVD diamond for detector applications

Energy Technology Data Exchange (ETDEWEB)

Adam, W. [HEPHY, Vienna (Austria); Berdermann, E. [GSI, Darmstadt (Germany); Bergonzo, P.; Brambilla, A. [LETI/DEIN/SPE/CEA Saclay (France); Boer, W. de [Universitaet Karlsruhe, Karlsruhe (Germany); Bogani, F. [LENS, Florence (Italy); Borchi, E.; Bruzzi, M. [University of Florence (Italy); Colledani, C.; Dulinski, W. [LEPSI, IN2P3/CNRS-ULP, Strasbourg (France); Conway, J.; Doroshenko, J. [Rutgers University, Piscataway (United States); D' Angelo, P.; Furetta, C. [INFN, Milano (Italy); Dabrowski, W. [UMM, Cracow (Poland); Delpierre, P.; Fallou, A. [CPPM, Marseille (France); Eijk, B. van [NIKHEF, Amsterdam (Netherlands); Fischer, P. [Universitaet Bonn, Bonn (Germany); Fizzotti, F. [University of Torino (Italy); Gan, K.K.; Ghodbane, N.; Grigoriev, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kaplon, J.; Kass, R.; Keil, M.; Knoepfle, K.T.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D.; Menichelli, D.; Meuser, S.; Mishina, M.; Moroni, L.; Noomen, J.; Oh, A.; Pernicka, M.; Perera, L.; Potenza, R.; Riester, J.L.; Roe, S.; Rudge, A.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Sutera, C.; Trischuk, W.; Tromson, D.; Tuve, C.; Vincenzo, B.; Weilhammer, P.; Wermes, N.; Wetstein, M.; Zeuner, W.; Zoeller, M.

2004-07-01

Chemical Vapor Deposition (CVD) diamond has been discussed extensively as an alternative sensor material for use very close to the interaction region of the LHC and other machines where extreme radiation conditions exist. During the last seven years the RD42 collaboration has developed diamond detectors and tested them with LHC electronics towards the end of creating a device usable by experiments. The most recent results of this work are presented. Recently, a new form of CVD diamond has been developed: single crystal CVD diamond which resolves many of the issues associated with poly-crystalline CVD material. The first tests of this material are also presented. (orig.)

New developments in CVD diamond for detector applications

International Nuclear Information System (INIS)

Adam, W.; Berdermann, E.; Bergonzo, P.; Brambilla, A.; Boer, W. de; Bogani, F.; Borchi, E.; Bruzzi, M.; Colledani, C.; Dulinski, W.; Conway, J.; Doroshenko, J.; D'Angelo, P.; Furetta, C.; Dabrowski, W.; Delpierre, P.; Fallou, A.; Eijk, B. van; Fischer, P.; Fizzotti, F.; Gan, K.K.; Ghodbane, N.; Grigoriev, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kaplon, J.; Kass, R.; Keil, M.; Knoepfle, K.T.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D.; Menichelli, D.; Meuser, S.; Mishina, M.; Moroni, L.; Noomen, J.; Oh, A.; Pernicka, M.; Perera, L.; Potenza, R.; Riester, J.L.; Roe, S.; Rudge, A.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Sutera, C.; Trischuk, W.; Tromson, D.; Tuve, C.; Vincenzo, B.; Weilhammer, P.; Wermes, N.; Wetstein, M.; Zeuner, W.; Zoeller, M.

2004-01-01

Chemical Vapor Deposition (CVD) diamond has been discussed extensively as an alternative sensor material for use very close to the interaction region of the LHC and other machines where extreme radiation conditions exist. During the last seven years the RD42 collaboration has developed diamond detectors and tested them with LHC electronics towards the end of creating a device usable by experiments. The most recent results of this work are presented. Recently, a new form of CVD diamond has been developed: single crystal CVD diamond which resolves many of the issues associated with poly-crystalline CVD material. The first tests of this material are also presented. (orig.)

Polarity Control of Heteroepitaxial GaN Nanowires on Diamond.

Science.gov (United States)

Hetzl, Martin; Kraut, Max; Hoffmann, Theresa; Stutzmann, Martin

2017-06-14

Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

RenderGAN: Generating Realistic Labeled Data

Directory of Open Access Journals (Sweden)

Leon Sixt

2018-06-01

Full Text Available Deep Convolutional Neuronal Networks (DCNNs are showing remarkable performance on many computer vision tasks. Due to their large parameter space, they require many labeled samples when trained in a supervised setting. The costs of annotating data manually can render the use of DCNNs infeasible. We present a novel framework called RenderGAN that can generate large amounts of realistic, labeled images by combining a 3D model and the Generative Adversarial Network framework. In our approach, image augmentations (e.g., lighting, background, and detail are learned from unlabeled data such that the generated images are strikingly realistic while preserving the labels known from the 3D model. We apply the RenderGAN framework to generate images of barcode-like markers that are attached to honeybees. Training a DCNN on data generated by the RenderGAN yields considerably better performance than training it on various baselines.

High-Sensitivity GaN Microchemical Sensors

Science.gov (United States)

Son, Kyung-ah; Yang, Baohua; Liao, Anna; Moon, Jeongsun; Prokopuk, Nicholas

2009-01-01

Systematic studies have been performed on the sensitivity of GaN HEMT (high electron mobility transistor) sensors using various gate electrode designs and operational parameters. The results here show that a higher sensitivity can be achieved with a larger W/L ratio (W = gate width, L = gate length) at a given D (D = source-drain distance), and multi-finger gate electrodes offer a higher sensitivity than a one-finger gate electrode. In terms of operating conditions, sensor sensitivity is strongly dependent on transconductance of the sensor. The highest sensitivity can be achieved at the gate voltage where the slope of the transconductance curve is the largest. This work provides critical information about how the gate electrode of a GaN HEMT, which has been identified as the most sensitive among GaN microsensors, needs to be designed, and what operation parameters should be used for high sensitivity detection.

Micro-strip sensors based on CVD diamond

Energy Technology Data Exchange (ETDEWEB)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D' Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; Eijk, B. van; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K.K.; Gheeraert, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D. E-mail: dirk.meier@cern.ch; Mishina, M.; Moroni, L.; Oh, A.; Pan, L.S.; Pernicka, M.; Peitz, A.; Perera, L.; Pirollo, S.; Procario, M.; Riester, J.L.; Roe, S.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R.J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Walsh, A.M.; Wedenig, R.; Weilhammer, P.; Wetstein, M.; White, C.; Zeuner, W.; Zoeller, M

2000-10-11

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

Micro-strip sensors based on CVD Diamond

CERN Document Server

Adam, W; Bergonzo, P; Bertuccio, G; Bogani, F; Borchi, E; Brambilla, A; Bruzzi, Mara; Colledani, C; Conway, J; D'Angelo, P; Dabrowski, W; Delpierre, P A; Deneuville, A; Dulinski, W; van Eijk, B; Fallou, A; Fizzotti, F; Foulon, F; Friedl, M; Gan, K K; Gheeraert, E; Hallewell, G D; Han, S; Hartjes, F G; Hrubec, Josef; Husson, D; Kagan, H; Kania, D R; Kaplon, J; Kass, R; Koeth, T W; Krammer, Manfred; Lo Giudice, A; Lü, R; MacLynne, L; Manfredotti, C; Meier, D; Mishina, M; Moroni, L; Oh, A; Pan, L S; Pernicka, Manfred; Peitz, A; Perera, L P; Pirollo, S; Procario, M; Riester, J L; Roe, S; Rousseau, L; Rudge, A; Russ, J; Sala, S; Sampietro, M; Schnetzer, S R; Sciortino, S; Stelzer, H; Stone, R; Suter, B; Tapper, R J; Tesarek, R J; Trischuk, W; Tromson, D; Vittone, E; Walsh, A M; Wedenig, R; Weilhammer, Peter; Wetstein, M; White, C; Zeuner, W; Zoeller, M M

2000-01-01

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

Micro-strip sensors based on CVD diamond

International Nuclear Information System (INIS)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; Eijk, B. van; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K.K.; Gheeraert, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; Mac Lynne, L.; Manfredotti, C.; Meier, D.; Mishina, M.; Moroni, L.; Oh, A.; Pan, L.S.; Pernicka, M.; Peitz, A.; Perera, L.; Pirollo, S.; Procario, M.; Riester, J.L.; Roe, S.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R.J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Walsh, A.M.; Wedenig, R.; Weilhammer, P.; Wetstein, M.; White, C.; Zeuner, W.; Zoeller, M.

2000-01-01

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation

Micro-strip sensors based on CVD diamond

Science.gov (United States)

Adam, W.; Berdermann, E.; Bergonzo, P.; Bertuccio, G.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; D'Angelo, P.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; van Eijk, B.; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K. K.; Gheeraert, E.; Hallewell, G.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Koeth, T.; Krammer, M.; Logiudice, A.; Lu, R.; mac Lynne, L.; Manfredotti, C.; Meier, D.; Mishina, M.; Moroni, L.; Oh, A.; Pan, L. S.; Pernicka, M.; Peitz, A.; Perera, L.; Pirollo, S.; Procario, M.; Riester, J. L.; Roe, S.; Rousseau, L.; Rudge, A.; Russ, J.; Sala, S.; Sampietro, M.; Schnetzer, S.; Sciortino, S.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R. J.; Tesarek, R.; Trischuk, W.; Tromson, D.; Vittone, E.; Walsh, A. M.; Wedenig, R.; Weilhammer, P.; Wetstein, M.; White, C.; Zeuner, W.; Zoeller, M.; RD42 Collaboration

2000-10-01

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

GaN membrane MSM ultraviolet photodetectors

Science.gov (United States)

Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

2006-12-01

GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

Surface chemistry and electronic structure of nonpolar and polar GaN films

Energy Technology Data Exchange (ETDEWEB)

Mishra, Monu; Krishna, T.C. Shibin; Aggarwal, Neha; Gupta, Govind, E-mail: govind@nplindia.org

2015-08-01

Highlights: • Surface chemistry and electronic structure of polar and nonpolar GaN is reported. • Influence of polarization on electron affinity of p & np GaN films is investigated. • Correlation between surface morphology and polarity has been deduced. - Abstract: Photoemission and microscopic analysis of nonpolar (a-GaN/r-Sapphire) and polar (c-GaN/c-Sapphire) epitaxial gallium nitride (GaN) films grown via RF-Molecular Beam Epitaxy is reported. The effect of polarization on surface properties like surface states, electronic structure, chemical bonding and morphology has been investigated and correlated. It was observed that polarization lead to shifts in core level (CL) as well as valence band (VB) spectra. Angle dependent X-ray Photoelectron Spectroscopic analysis revealed higher surface oxide in polar GaN film compared to nonpolar GaN film. On varying the take off angle (TOA) from 0° to 60°, the Ga−O/Ga−N ratio varied from 0.11–0.23 for nonpolar and 0.17–0.36 for polar GaN film. The nonpolar film exhibited N-face polarity while Ga-face polarity was perceived in polar GaN film due to the inherent polarization effect. Polarization charge compensated surface states were observed on the polar GaN film and resulted in downward band bending. Ultraviolet photoelectron spectroscopic measurements revealed electron affinity and ionization energy of 3.4 ± 0.1 eV and 6.8 ± 0.1 eV for nonpolar GaN film and 3.8 ± 0.1 eV and 7.2 ± 0.1 eV for polar GaN film respectively. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with pits on polar GaN film. The nonpolar film on the other hand showed pyramidal structures having facets all over the surface.

Conductivity based on selective etch for GaN devices and applications thereof

Science.gov (United States)

Zhang, Yu; Sun, Qian; Han, Jung

2015-12-08

This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

Characterization of vertical GaN p-n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

Science.gov (United States)

Kizilyalli, I. C.; Aktas, O.

2015-12-01

There is great interest in wide-bandgap semiconductor devices and most recently in vertical GaN structures for power electronic applications such as power supplies, solar inverters and motor drives. In this paper the temperature-dependent electrical behavior of vertical GaN p-n diodes and vertical junction field-effect transistors fabricated on bulk GaN substrates of low defect density (104 to 106 cm-2) is described. Homoepitaxial MOCVD growth of GaN on its native substrate and the ability to control the doping in the drift layers in GaN have allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations as low as 1 × 1015 cm-3. This parameter range is suitable for applications requiring breakdown voltages of 1.2 kV to 5 kV. Mg, which is used as a p-type dopant in GaN, is a relatively deep acceptor (E A ≈ 0.18 eV) and susceptible to freeze-out at temperatures below 200 K. The loss of holes in p-GaN has a deleterious effect on p-n junction behavior, p-GaN contacts and channel control in junction field-effect transistors at temperatures below 200 K. Impact ionization-based avalanche breakdown (BV > 1200 V) in GaN p-n junctions is characterized between 77 K and 423 K for the first time. At higher temperatures the p-n junction breakdown voltage improves due to increased phonon scattering. A positive temperature coefficient in the breakdown voltage is demonstrated down to 77 K; however, the device breakdown characteristics are not as abrupt at temperatures below 200 K. On the other hand, contact resistance to p-GaN is reduced dramatically above room temperature, improving the overall device performance in GaN p-n diodes in all cases except where the n-type drift region resistance dominates the total forward resistance. In this case, the electron mobility can be deconvolved and is found to decrease with T -3/2, consistent with a phonon scattering model. Also, normally-on vertical junction

Thermodynamic analysis of Mg-doped p-type GaN semiconductor

International Nuclear Information System (INIS)

Li Jingbo; Liang Jingkui; Rao Guanghui; Zhang Yi; Liu Guangyao; Chen Jingran; Liu Quanlin; Zhang Weijing

2006-01-01

A thermodynamic modeling of Mg-doped p-type GaN was carried out to describe the thermodynamic behaviors of native defects, dopants (Mg and H) and carriers in GaN. The formation energies of charged component compounds in a four-sublattice model were defined as functions of the Fermi-level based on the results of the first-principles calculations and adjusted to fit experimental data. The effect of the solubility of Mg on the low doping efficiency of Mg in GaN and the role of H in the Mg-doping MOCVD process were discussed. The modeling provides a thermodynamic approach to understand the doping process of GaN semiconductors

An optical emission spectroscopy study of the plasma generated in the DC HF CVD nucleation of diamond

Energy Technology Data Exchange (ETDEWEB)

Larijani, M.M. [Nuclear Research Centre for Agriculture and Medicine, AEOI, P.O. Box 31485-498, Karaj (Iran, Islamic Republic of)]. E-mail: mmojtahedzadeh@nrcam.org; Le Normand, F. [Groupe Surfaces-Interfaces, IPCMS, UMR 7504 CNRS, BP 20, 67037 Strasbourg Cedex 2 (France); Cregut, O. [Groupe Surfaces-Interfaces, IPCMS, UMR 7504 CNRS, BP 20, 67037 Strasbourg Cedex 2 (France)

2007-02-15

Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH{sub 4} + H{sub 2} both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of H{sub {beta}}-H{sub {alpha}} implying an increase of electron mean energy, as well as CH, CH{sup +}, C{sub 2}. A correlation between the relative increase of CH{sup +} and the diamond nucleation density was found, conversely the increase of C{sub 2} contributed to the introduction of defects in the diamond nuclei.

A measure of the interfacial shear strength between SiC(CVD)/B(CVD) filament--aluminum matrix by fragmentation method

International Nuclear Information System (INIS)

Jiang, Y.Q.; Chen, X.J.; Yang, D.M.; Fei, X.; Pan, J.

1993-01-01

The tensile specimens used are of dog-bone shape and consist of single axial SiC (CVD) /B (CVD) filament processed by CVD and embedded in a LD-2 aluminum alloy. Model composite specimens have been fabricated by a high pressure squeeze casting technique. This paper describes the application of an Acoustic Emission Technique for locating the position of fiber breaks and thus determining the length distribution of fiber fragments resulting when a composite specimen containing a single fiber is loaded to failure. The critical lengths (minimal lengths) are checked by Corrosion Method

An assessment of radiotherapy dosimeters based on CVD grown diamond

International Nuclear Information System (INIS)

Ramkumar, S.; Buttar, C.M.; Conway, J.; Whitehead, A.J.; Sussman, R.S.; Hill, G.; Walker, S.

2001-01-01

Diamond is potentially a very suitable material for use as a dosimeter for radiotherapy. Its radiation hardness, the near tissue equivalence and chemical inertness are some of the characteristics of diamond, which make it well suited for its application as a dosimeter. Recent advances in the synthesis of diamond by chemical vapour deposition (CVD) technology have resulted in the improvement in the quality of material and increased its suitability for radiotherapy applications. We report in this paper, the response of prototype dosimeters based on two different types (CVD1 and CVD2) of CVD diamond to X-rays. The diamond devices were assessed for sensitivity, dependence of response on dose and dose rate, and compared with a Scanditronix silicon photon diode and a PTW natural diamond dosimeter. The diamond devices of CVD1 type showed an initial increase in response with dose, which saturates after ∼6 Gy. The diamond devices of CVD2 type had a response at low fields ( 1162.8 V/cm), the CVD2-type devices showed polarisation and dose-rate dependence. The sensitivity of the CVD diamond devices varied between 82 and 1300 nC/Gy depending upon the sample type and the applied voltage. The sensitivity of CVD diamond devices was significantly higher than that of natural diamond and silicon dosimeters. The results suggest that CVD diamond devices can be fabricated for successful use in radiotherapy applications

Growth on nonpolar and semipolar GaN: The substrate dilemma

Energy Technology Data Exchange (ETDEWEB)

Wernicke, T.; Weyers, M. [Ferdinand-Braun-Institute, Berlin (Germany); Kneissl, M. [Ferdinand-Braun-Institute, Berlin (Germany); Institute of Solid State Physics, TU Berlin (Germany)

2009-07-01

Growth of nonpolar and semipolar GaN is very promising for achieving green laser diodes (LDs). However, the choice of the substrate is a difficult one: Heteroepitaxial growth on sapphire, SiC, LiAlO{sub 2} yields GaN films with a poor surface quality and high defect densities. On the other hand non- and semipolar bulk GaN substrates provide excellent crystal quality, but are so far only available in very small sizes. In this paper hetero- and homoepitaxial growth is compared. For all heteroepitaxially grown semi- and nonpolar GaN layers threading dislocations (TD) and basal plane stacking faults (BSF) can be found. There are four possible mechanisms for the generation of BSF: Growth of the N-polar basal plane, formation during nucleation at substrate steps, formation at the coalescence front of differently stacked nucleation islands, and generation at planar defects occurring in m-plane GaN on LiAlO{sub 2}. BSF induce surface roughening and are associated with partial dislocations causing nonradiative recombination. Thus they affect the performance of devices. We show that BSFs and TDs can be reduced by epitaxial lateral overgrowth resulting in several micrometer wide defect free areas. However, for LEDs larger defect-free areas are required. GaN layers grown on bulk GaN substrates exhibit a high crystal quality, but show in many cases long-range surface structures with a height of {approx}1{mu}m.

Comparison of PIV and Hot-Wire statistics of turbulent boundary layer

International Nuclear Information System (INIS)

Dróżdż, A; Uruba, V

2014-01-01

The paper shows a cross checking of turbulent boundary layer measurements using large field of view PIV and hot-wire anemometry techniques. The time-resolved PIV method was used for the experiments. The measuring plane was oriented perpendicularly to the wall and parallel to the mean flow. Hot wire measurement has been performed using the special probe with perpendicular hot wire. The HW point measurements were performed in the same place as PIV experiments. The hot-wire probe has the wire length of l + < 20 in considered range of Reynolds numbers. Various evaluation methods were applied on PIV data. The profiles of statistical characteristics of streamwise velocity components were evaluated from the data. Mean values, standard deviations as well as skewness and kurtosis coefficients were compared for a few values of Re θ . Reynolds number ranges from 1000 to 5500. The result shows that with the increasing Reynolds number the attenuation of fluctuations maximum in PIV measurements occurs with respect to Hot-Wire measurements, however representation of velocity fluctuations using the PIV method is satisfactory. The influence of wall-normal fluctuation component on Hot-Wire near wall peak was also investigated.

Highly c-axis oriented growth of GaN film on sapphire (0001 by laser molecular beam epitaxy using HVPE grown GaN bulk target

Directory of Open Access Journals (Sweden)

S. S. Kushvaha

2013-09-01

Full Text Available Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001 substrates by laser molecular beam epitaxy (LMBE were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM, micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS. The x-ray rocking curve full width at a half maximum (FWHM value for (0002 reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002 plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

Synthesis and Raman scattering of GaN nanorings, nanoribbons and nanowires

Energy Technology Data Exchange (ETDEWEB)

Li, Z.J. [Academia Sinica, Beijing, BJ (China). Inst. of Physics; Northwestern Polytechnical Univ., Xian, SN (China). Dept. of Materials Science and Engineering; Chen, X.L.; Tu, Q.Y.; Yang, Z.; Xu, Y.P.; Hu, B.Q. [Academia Sinica, Beijing, BJ (China). Inst. of Physics; Li, H.J. [Northwestern Polytechnical Univ., Xian, SN (China). Dept. of Materials Science and Engineering

2001-05-01

Low-dimensional GaN materials, including nanorings, nanoribbons and smooth nanowires have been synthesized by reacting gallium and ammonia using Ag particles as a catalyst on the substrate of MgO single crystals. They were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). EDX, XRD indicated that the low-dimensional nanomaterials were wurtzite GaN. New features are found in Raman scatterings for these low-dimensional GaN materials, which are different from the previous observations of GaN materials. (orig.)

GaN and LED structures grown on pre-patterned silicon pillar arrays

Energy Technology Data Exchange (ETDEWEB)

Li, Shunfeng; Fuendling, Soenke; Soekmen, Uensal; Merzsch, Stephan; Neumann, Richard; Peiner, Erwin; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Hinze, Peter; Weimann, Thomas [Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany); Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvoigteiplatz 5-7, 10117 Berlin (Germany)

2010-01-15

GaN nanorods (or nanowires) have attracted great interest in a variety of applications, e.g. high-efficiency light emitting diodes, monolithic white light emission and optical interconnection due to their superior properties. In contrast to the mostly investigated self-assembled growth of GaN nanorods, we performed GaN nanorod growth by pre-patterning of the Si substrates. The pattern was transferred to Si substrates by photolithography and cryo-temperature inductively-coupled plasma etching. These Si templates then were used for further GaN nanorod growth by metal-organic vapour phase epitaxy (MOVPE). The low temperature AlN nucleation layer had to be optimized since it differs from its 2D layer counterpart on the surface area and orientations. We found a strong influence of diffusion processes, i.e. the GaN grown on top of the Si nanopillars can deplete the GaN around the Si pillars. Transmission electron microscopy measurements demonstrated clearly that the threading dislocations bend to the side facets of the pyramidal GaN nanostructures and terminate. Cathodoluminescence measurements reveal a difference of In composition and/or thickness of InGaN quantum wells on the different facets of the pyramidal GaN nanostructures. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Red shift of near band edge emission in cerium implanted GaN

International Nuclear Information System (INIS)

Majid, Abdul; Ali, Akbar

2009-01-01

Rare earth (RE) doping in GaN is a promising technology to control the optical properties. However, there are no reports on doping of cerium (Ce) into GaN, which is a very unique RE element. In this paper, we performed photoluminescence (PL) and optical transmission measurements on Ce-doped GaN for the first time. A significant red shift of about 120 meV was observed in the PL peak position of the donor bound excitons. This red shift of near band emission was corroborated by the red shift of the absorption edge related to GaN in the optical transmission measurements. This observation is attributed to the band gap narrowing in GaN heavily doped with Ce. The activation energy of the Ce-related shallow donor is found to be 21.9 meV in GaN.

Red shift of near band edge emission in cerium implanted GaN

Energy Technology Data Exchange (ETDEWEB)

Majid, Abdul; Ali, Akbar, E-mail: abdulmajid40@yahoo.co, E-mail: akbar@qau.edu.p [Advance Materials Physics Laboratory, Physics Department, Quaid-i-Azam University, Islamabad (Pakistan)

2009-02-21

Rare earth (RE) doping in GaN is a promising technology to control the optical properties. However, there are no reports on doping of cerium (Ce) into GaN, which is a very unique RE element. In this paper, we performed photoluminescence (PL) and optical transmission measurements on Ce-doped GaN for the first time. A significant red shift of about 120 meV was observed in the PL peak position of the donor bound excitons. This red shift of near band emission was corroborated by the red shift of the absorption edge related to GaN in the optical transmission measurements. This observation is attributed to the band gap narrowing in GaN heavily doped with Ce. The activation energy of the Ce-related shallow donor is found to be 21.9 meV in GaN.

Positron annihilation study of Pd contacts on impurity-doped GaN

International Nuclear Information System (INIS)

Lee, Jong-Lam; Kim, Jong Kyu; Weber, Marc H.; Lynn, Kelvin G.

2001-01-01

Pd contacts on both n-type and p-type GaN were studied using positron annihilation spectroscopy, and the results were used to interpret the role of Ga vacancies on the band bending below the contacts. The concentration of Ga vacancy in Si-doped GaN was higher than that in the Mg-doped one. In Si-doped GaN, implanted positrons were annihilated at the nearer surface region and the interface of Pd/n-type GaN was detected by positrons clearly shifted toward the surface of Pd. This suggests that Ga vacancies could act as an interface state, pinning the Fermi level at the interface of Pd with GaN, leading to the production of a negative electric field below the interface. [copyright] 2001 American Institute of Physics

Control of residual carbon concentration in GaN high electron mobility transistor and realization of high-resistance GaN grown by metal-organic chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

He, X.G. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhao, D.G., E-mail: dgzhao@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, D.S.; Liu, Z.S.; Chen, P.; Le, L.C.; Yang, J.; Li, X.J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang, S.M.; Zhu, J.J.; Wang, H.; Yang, H. [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China)

2014-08-01

GaN films were grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions. The influences of MOCVD growth parameters, i.e., growth pressure, ammonia (NH{sub 3}) flux, growth temperature, trimethyl-gallium flux and H{sub 2} flux, on residual carbon concentration ([C]) were systematically investigated. Secondary ion mass spectroscopy measurements show that [C] can be effectively modulated by growth conditions. Especially, it can increase by reducing growth pressure up to two orders of magnitude. High-resistance (HR) GaN epilayer with a resistivity over 1.0 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. The mechanism of the formation of HR GaN epilayer is discussed. An Al{sub x}Ga{sub 1−x}N/GaN high electron mobility transistor structure with a HR GaN buffer layer and an additional low-carbon GaN channel layer is presented, exhibiting a high two dimensional electron gas mobility of 1815 cm{sup 2}/Vs. - Highlights: • Influence of MOCVD parameters on residual carbon concentration in GaN is studied. • GaN layer with a resistivity over 1 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. • High electron mobility transistor (HEMT) structures were prepared. • Control of residual carbon content results in HEMT with high 2-D electron gas mobility.

A Frontal Attack on Limiting Defects in GaN

National Research Council Canada - National Science Library

Morkoc, Hadis

2002-01-01

GaN community, particularly under the leadership of Drs. Wood, Win, and Litton, recognized that it is imperative that the extended, and point defects in GaN and related materials, and the mechanisms for their formation are understood...

Seismic evaluation of a hot cell structure

International Nuclear Information System (INIS)

Srinivasan, M.G.; Kot, C.A.

1995-01-01

The evaluation of the structural capacity of and the seismic demand on an existing hot cell structure in a nuclear facility is described. An ANSYS finite-element model of the cell was constructed, treating the walls as plates and the floor and ceiling as a system of discrete beams. A modal analysis showed that the fundamental frequencies of the cell walls lie far above the earthquake frequency range. An equivalent static analysis of the structure was performed. Based on the analysis it was demonstrated that the hot cell structure, would readily withstand the evaluation basis earthquake

The origin of the residual conductivity of GaN films on ferroelectric materials

Science.gov (United States)

Lee, Kyoung-Keun; Cai, Zhuhua; Ziemer, Katherine; Doolittle, William Alan

2009-08-01

In this paper, the origin of the conductivity of GaN films grown on ferroelectric materials was investigated using XPS, AES, and XRD analysis tools. Depth profiles confirmed the existence of impurities in the GaN film originating from the substrates. Bonding energy analysis from XPS and AES verified that oxygen impurities from the substrates were the dominant origin of the conductivity of the GaN film. Furthermore, Ga-rich GaN films have a greater chance of enhancing diffusion of lithium oxide from the substrates, resulting in more substrate phase separation and a wider inter-mixed region confirmed by XRD. Therefore, the direct GaN film growth on ferroelectric materials causes impurity diffusion from the substrates, resulting in highly conductive GaN films. Future work needs to develop non-conductive buffer layers for impurity suppression in order to obtain highly resistive GaN films.

Semi-polar GaN heteroepitaxy an high index Si-surfaces

Energy Technology Data Exchange (ETDEWEB)

Ravash, Roghaiyeh; Blaesing, Juergen; Hempel, Thomas; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-University Magdeburg, FNW/IEP/AHE, Magdeburg (Germany)

2011-07-01

Due to the lack of GaN homosubstrates, the growth of GaN-based devices is usually performed on heterosubstrates as sapphire or SiC. These substrates are either insulating or expensive, and both unavailable in large diameters. Meanwhile, silicon can meet the requirements for a low price and thermally well conducting substrate and also enabling the integration of optoelectronic devices with Si-based electronics. Up to now, the good matching of hexagonal GaN with the three-fold symmetry of Si(111) greatly promotes the c-axis orientated growth of GaN on this surface plane. A large spontaneous and piezoelectric polarization oriented along the c-axis exists in such hexagonal structure leading to low efficiencies for thick quantum wells. The attention to the growth of non-polar or semi-polar GaN based epitaxial structures has been increased recently because of reducing the effect of the polarization fields in these growth directions. Therefore we studied semi-polar GaN epilayers grown by metalorganic vapor phase epitaxy on silicon substrates with different orientations from Si(211) to Si(711). We observed that AlN seeding layer growth time play a significant role in obtaining the different GaN texture.

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

Science.gov (United States)

Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

2015-09-02

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

Effects of thin heavily Mg-doped GaN capping layer on ohmic contact formation of p-type GaN

International Nuclear Information System (INIS)

Wu, L L; Zhao, D G; Jiang, D S; Chen, P; Le, L C; Li, L; Liu, Z S; Zhang, S M; Zhu, J J; Wang, H; Zhang, B S; Yang, H

2013-01-01

The growth condition of thin heavily Mg-doped GaN capping layer and its effect on ohmic contact formation of p-type GaN were investigated. It is confirmed that the excessive Mg doping can effectively enhance the Ni/Au contact to p-GaN after annealing at 550 °C. When the flow rate ratio between Mg and Ga gas sources is 6.4% and the layer width is 25 nm, the capping layer grown at 850 °C exhibits the best ohmic contact properties with respect to the specific contact resistivity (ρ c ). This temperature is much lower than the conventional growth temperature of Mg-doped GaN, suggesting that the deep-level-defect induced band may play an important role in the conduction of capping layer. (paper)

Vertical GaN Devices for Power Electronics in Extreme Environments

Science.gov (United States)

2016-03-31

Vertical GaN Devices for Power Electronics in Extreme Environments Isik C. Kizilyalli (1), Robert J. Kaplar (2), O. Aktas (1), A. M. Armstrong (2...electronics applications. In this paper vertical p-n diodes and transistors fabricated on pseudo bulk low defect density (104 to 106 cm-2) GaN substrates are...discussed. Homoepitaxial MOCVD growth of GaN on its native substrate and being able to control doping has allowed the realization of vertical

Hot wire chemical vapor deposition: limits and opportunities of protecting the tungsten catalyzer from silicide with a cavity

International Nuclear Information System (INIS)

Frigeri, P.A.; Nos, O.; Bengoechea, S.; Frevert, C.; Asensi, J.M.; Bertomeu, J.

2009-01-01

Hot Wire Chemical Vapor Deposition (HW-CVD) is one of the most promising techniques for depositing the intrinsic microcrystalline silicon layer for the production of micro-morph solar cells. However, the silicide formation at the colder ends of the tungsten wire drastically reduces the lifetime of the catalyzer, thus limiting its industrial exploitation. A simple but interesting strategy to decrease the silicide formation is to hide the electrical contacts of the catalyzer in a long narrow cavity which reduces the probability of the silane molecules to reach the colder ends of the wire. In this paper, the working mechanism of the cavity is elucidated. Measurements of the thickness profile of the silicon deposited in the internal walls of the cavity have been compared with those predicted using a simple diffusion model based on the assumption of Knudsen flow. A lifetime study of the protected and unprotected wires has been carried out. The different mechanisms which determine the deterioration of the catalyzer have been identified and discussed.

En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays

Directory of Open Access Journals (Sweden)

Slawomir Boncel

2014-03-01

Full Text Available The catalytic chemical vapour deposition (c-CVD technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs. A mixture of toluene (main carbon source, pyrazine (1,4-diazine, nitrogen source and ferrocene (catalyst precursor was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C, composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs. As revealed by electron microscopy studies (SEM, TEM, the individual N-CNTs (half as thick as MWCNTs grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor. In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type type as compared to the purely �

En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays.

Science.gov (United States)

Boncel, Slawomir; Pattinson, Sebastian W; Geiser, Valérie; Shaffer, Milo S P; Koziol, Krzysztof K K

2014-01-01

The catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 10(8) nanotubes per mm(2) (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a 'bamboo'-like or 'membrane'-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp(2)-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a 'mixed base-and-tip' (primarily of the base-type) type as compared to the purely 'base'-type for undoped

Piezo-generator integrating a vertical array of GaN nanowires.

Science.gov (United States)

Jamond, N; Chrétien, P; Houzé, F; Lu, L; Largeau, L; Maugain, O; Travers, L; Harmand, J C; Glas, F; Lefeuvre, E; Tchernycheva, M; Gogneau, N

2016-08-12

We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

CVD Diamond Sensors In Detectors For High Energy Physics

CERN Document Server

AUTHOR|(INSPIRE)INSPIRE-00334150; Trischuk, William

At the end of the next decade an upgrade of the Large Hadron Collider (LHC) to High Luminosity LHC (HL-LHC) is planned which requires the development of new radiation tolerant sensor technology. Diamond is an interesting material for use as a particle detector in high radiation environments. The large band gap ($5.47\\,\\text{eV}$) and the large displacement energy suggest that diamond is a radiation tolerant detector material. In this Thesis the capability of Chemical Vapor Deposition (CVD) diamond as such a sensor technology is investigated. The radiation damage constant for $800\\,\\text{MeV}$ protons is measured using single crystalline CVD (scCVD) and polycrystalline CVD (pCVD) diamonds irradiated to particle fluences up to $12 \\times 10^{15}\\,\\text{p/cm}^2$. In addition the signal response of a pCVD diamond detector after an irradiation to $12 \\times 10^{15}\\,\\text{p/cm}^2$ is investigated to determine if such a detector can be operated efficiently in the expected HL-LHC environment. By using electrodes em...

Characterization of vertical GaN p–n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

International Nuclear Information System (INIS)

Kizilyalli, I C; Aktas, O

2015-01-01

There is great interest in wide-bandgap semiconductor devices and most recently in vertical GaN structures for power electronic applications such as power supplies, solar inverters and motor drives. In this paper the temperature-dependent electrical behavior of vertical GaN p–n diodes and vertical junction field-effect transistors fabricated on bulk GaN substrates of low defect density (10 4 to 10 6 cm −2 ) is described. Homoepitaxial MOCVD growth of GaN on its native substrate and the ability to control the doping in the drift layers in GaN have allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations as low as 1 × 10 15 cm −3 . This parameter range is suitable for applications requiring breakdown voltages of 1.2 kV to 5 kV. Mg, which is used as a p-type dopant in GaN, is a relatively deep acceptor (E A  ≈ 0.18 eV) and susceptible to freeze-out at temperatures below 200 K. The loss of holes in p-GaN has a deleterious effect on p–n junction behavior, p-GaN contacts and channel control in junction field-effect transistors at temperatures below 200 K. Impact ionization-based avalanche breakdown (BV > 1200 V) in GaN p–n junctions is characterized between 77 K and 423 K for the first time. At higher temperatures the p–n junction breakdown voltage improves due to increased phonon scattering. A positive temperature coefficient in the breakdown voltage is demonstrated down to 77 K; however, the device breakdown characteristics are not as abrupt at temperatures below 200 K. On the other hand, contact resistance to p-GaN is reduced dramatically above room temperature, improving the overall device performance in GaN p–n diodes in all cases except where the n-type drift region resistance dominates the total forward resistance. In this case, the electron mobility can be deconvolved and is found to decrease with T −3/2 , consistent with a phonon scattering model. Also

Spin injection in epitaxial MnGa(111)/GaN(0001) heterostructures

Science.gov (United States)

Zube, Christian; Malindretos, Joerg; Watschke, Lars; Zamani, Reza R.; Disterheft, David; Ulbrich, Rainer G.; Rizzi, Angela; Iza, Michael; Keller, Stacia; DenBaars, Steven P.

2018-01-01

Ferromagnetic MnGa(111) layers were grown on GaN(0001) by molecular beam epitaxy. MnGa/GaN Schottky diodes with a doping level of around n = 7 × 1018 cm-3 were fabricated to achieve single step tunneling across the metal/semiconductor junction. Below the GaN layer, a thin InGaN quantum well served as optical spin detector ("spin-LED"). For electron spin injection from MnGa into GaN and subsequent spin transport through a 45 nm (70 nm) thick GaN layer, we observe a circular polarization of 0.3% (0.2%) in the electroluminescence at 80 K. Interface mixing, spin polarization losses during electrical transport in the GaN layer, and spin relaxation in the InGaN quantum well are discussed in relation with the low value of the optically detected spin polarization.

Thermal Annealing induced relaxation of compressive strain in porous GaN structures

KAUST Repository

Ben Slimane, Ahmed; Najar, Adel; Ng, Tien Khee; Ooi, Boon S.

2012-01-01

The effect of annealing on strain relaxation in porous GaN fabricated using electroless chemical etching is presented. The Raman shift of 1 cm-1 in phonon frequency of annealed porous GaN with respect to as-grown GaN corresponds to a relaxation

Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.

Science.gov (United States)

Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil

2017-12-13

Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.

Comb-drive GaN micro-mirror on a GaN-on-silicon platform

International Nuclear Information System (INIS)

Wang, Yongjin; Sasaki, Takashi; Wu, Tong; Hu, Fangren; Hane, Kazuhiro

2011-01-01

We report here a double-sided process for the fabrication of a comb-drive GaN micro-mirror on a GaN-on-silicon platform. A silicon substrate is first patterned from the backside and removed by deep reactive ion etching, resulting in totally suspended GaN slabs. GaN microstructures including the torsion bars, movable combs and mirror plate are then defined on a freestanding GaN slab by the backside alignment technique and generated by fast atom beam etching with Cl 2 gas. Although the fabricated comb-drive GaN micro-mirrors are deflected by the residual stress in GaN thin films, they can operate on a high resistivity silicon substrate without introducing any additional isolation layer. The optical rotation angles are experimentally characterized in the rotation experiments. This work opens the possibility of producing GaN optical micro-electro-mechanical-system (MEMS) devices on a GaN-on-silicon platform.

Determination of carrier diffusion length in p- and n-type GaN

Science.gov (United States)

Hafiz, Shopan; Metzner, Sebastian; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Karbaum, Christopher; Bertram, Frank; Christen, Jürgen; Gil, Bernard; Özgür, Ümit

2014-03-01

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p- GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photogeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 ± 7 nm and 68 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm.

Application of Generative Adversarial Networks (GANs) to jet images

CERN Multimedia

CERN. Geneva

2017-01-01

https://arxiv.org/abs/1701.05927 We provide a bridge between generative modeling in the Machine Learning community and simulated physical processes in High Energy Particle Physics by applying a novel Generative Adversarial Network (GAN) architecture to the production of jet images -- 2D representations of energy depositions from particles interacting with a calorimeter. We propose a simple architecture, the Location-Aware Generative Adversarial Network, that learns to produce realistic radiation patterns from simulated high energy particle collisions. The pixel intensities of GAN-generated images faithfully span over many orders of magnitude and exhibit the desired low-dimensional physical properties (i.e., jet mass, n-subjettiness, etc.). We shed light on limitations, and provide a novel empirical validation of image quality and validity of GAN-produced simulations of the natural world. This work provides a base for further explorations of GANs for use in faster simulation in High Energy Particle Physics.

The gate oxide integrity of CVD tungsten polycide

International Nuclear Information System (INIS)

Wu, N.W.; Su, W.D.; Chang, S.W.; Tseng, M.F.

1988-01-01

CVD tungsten polycide has been demonstrated as a good gate material in recent very large scale integration (VLSI) technology. CVD tungsten silicide offers advantages of low resistivity, high temperature stability and good step coverage. On the other hand, the polysilicon underlayer preserves most characteristics of the polysilicon gate and acts as a stress buffer layer to absorb part of the thermal stress origin from the large thermal expansion coefficient of tungsten silicide. Nevertheless, the gate oxide of CVD tungsten polycide is less stable or reliable than that of polysilicon gate. In this paper, the gate oxide integrity of CVD tungsten polycide with various thickness combinations and different thermal processes have been analyzed by several electrical measurements including breakdown yield, breakdown fluence, room temperature TDDB, I-V characteristics, electron traps and interface state density

Mg doping and its effect on the semipolar GaN(1122) growth kinetics

International Nuclear Information System (INIS)

Lahourcade, L.; Wirthmueller, A.; Monroy, E.; Pernot, J.; Chauvat, M. P.; Ruterana, P.; Laufer, A.; Eickhoff, M.

2009-01-01

We report the effect of Mg doping on the growth kinetics of semipolar GaN(1122) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(1122). We observe an enhancement of Mg incorporation in GaN(1122) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

Use of GaN as a Scintillating Ionizing Radiation Detector

Science.gov (United States)

Wensman, Johnathan; Guardala, Noel; Mathur, Veerendra; Alasagas, Leslie; Vanhoy, Jeffrey; Statham, John; Marron, Daniel; Millett, Marshall; Marsh, Jarrod; Currie, John; Price, Jack

2017-09-01

Gallium nitride (GaN) is a III/V direct bandgap semiconductor which has been used in light emitting diodes (LEDs) since the 1990s. Currently, due to a potential for increased efficiency, GaN is being investigated as a replacement for silicon in power electronics finding potential uses ranging from data centers to electric vehicles. In addition to LEDs and power electronics though, doped GaN can be used as a gamma insensitive fast neutron detector due to the direct band-gap, light propagation properties, and response to ionizing radiations. Investigation of GaN as a semiconductor scintillator for use in a radiation detection system involves mapping the response function of the detector crystal over a range of photon and neutron energies, and measurements of light generation in the GaN crystal due to proton, alpha, and nitrogen projectiles. In this presentation we discuss the measurements made to date, and plausible interpretations of the response functions. This work funded in part by the Naval Surface Warfare Center, Carderock Division In-house Laboratory Independent Research program.

CVD mechanism of pyrolytic boron nitride

International Nuclear Information System (INIS)

Tanji, H.; Monden, K.; Ide, M.

1987-01-01

Pyrolytic boron nitride (P-BN) has become a essential material for III-V compound semiconductor manufacturing process. As the demand from electronics industry for larger single crystals increases, the demand for larger and more economical P-BN components is growing rapidly. P-BN is manufactured by low pressure CVD using boron-trihalides and ammonia as the reactants. In spite that P-BN has been in the market for quite a long time, limited number of fundamental studies regarding the kinetics and the formation mechanism of P-BN have been reported. As it has been demonstrated in CVD of Si, knowledge and both theoretical and empirical modeling of CVD process can be applied to improve the deposition technology and to give more uniform deposition with higher efficiency, and it should also apply to the deposition of P-BN

Carbon Nanotubes Growth by CVD on Graphite Fibers

Science.gov (United States)

Zhu, Shen; Su, Ching-Hua; Cochrane, J. C.; Lehoczky, S. L.; Muntele, I.; Ila, D.; Curreri, Peter A. (Technical Monitor)

2002-01-01

Due to the superior electrical and mechanical properties of carbon nanotubes (CNT), synthesizing CNT on various substances for electronics devices and reinforced composites have been engaged in many efforts for applications. This presentation will illustrate CNT synthesized on graphite fibers by thermal CVD. On the fiber surface, iron nanoparticles as catalysts for CNT growth are coated. The growth temperature ranges from 600 to 1000 C and the pressure ranges from 100 Torr to one atmosphere. Methane and hydrogen gases with methane content of 10% to 100% are used for the CNT synthesis. At high growth temperatures (greater than or equal to 900 C), the rapid inter-diffusion of the transition metal iron on the graphite surface results in the rough fiber surface without any CNT grown on it. When the growth temperature is relative low (650-800 C), CNT with catalytic particles on the nanotube top ends are fabricated on the graphite surface. (Methane and hydrogen gases with methane content of 10% to 100% are used for the CNT synthesis.) (By measuring the samples) Using micro Raman spectroscopy in the breath mode region, single-walled or multi-walled CNT (MWCNT), depending on growth concentrations, are found. Morphology, length and diameter of these MWCNT are determined by scanning electron microscopy and Raman spectroscopy. The detailed results of syntheses and characterizations will be discussed in the presentation.

Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

International Nuclear Information System (INIS)

Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong; Zhao, Degang; Zhang, Baolin; Du, Guotong

2016-01-01

Graphical abstract: - Highlights: • Effects of Mg doping on wet etching of N-polar GaN are illustrated and analysed. • Etching process model of Mg-doped N-polar GaN in KOH solution is purposed. • It is found that Mg doping can induce tensile strain in N-polar GaN film. • N-polar p-GaN film with a hole concentration of 2.4 × 10"1"7 cm"−"3 is obtained. - Abstract: KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 × 10"1"7 cm"−"3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

Energy Technology Data Exchange (ETDEWEB)

Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Qianjin Street 2699, Changchun 130012 (China); Zhao, Degang [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Science, PO Box 912, Beijing 100083 (China); Zhang, Baolin; Du, Guotong [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Qianjin Street 2699, Changchun 130012 (China)

2016-01-01

Graphical abstract: - Highlights: • Effects of Mg doping on wet etching of N-polar GaN are illustrated and analysed. • Etching process model of Mg-doped N-polar GaN in KOH solution is purposed. • It is found that Mg doping can induce tensile strain in N-polar GaN film. • N-polar p-GaN film with a hole concentration of 2.4 × 10{sup 17} cm{sup −3} is obtained. - Abstract: KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 × 10{sup 17} cm{sup −3} was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

Effect of annealing on metastable shallow acceptors in Mg-doped GaN layers grown on GaN substrates

OpenAIRE

Pozina, Galia; Hemmingsson, Carl; Paskov, Plamen P.; Bergman, Peder; Monemar, Bo; Kawashima, T.; Amano, H.; Akasaki, I.; Usui, A.

2008-01-01

Mg-doped GaN layers grown by metal-organic vapor phase epitaxy on GaN substrates produced by the halide vapor phase technique demonstrate metastability of the near-band-gap photoluminescence (PL). The acceptor bound exciton (ABE) line possibly related to the C acceptor vanishes in as-grown samples within a few minutes under UV laser illumination. Annealing activates the more stable Mg acceptors and passivates C acceptors. Consequently, only the ABE line related to Mg is dominant in PL spectra...

Modification of GaN(0001) growth kinetics by Mg doping

International Nuclear Information System (INIS)

Monroy, E.; Andreev, T.; Holliger, P.; Bellet-Amalric, E.; Shibata, T.; Tanaka, M.; Daudin, B.

2004-01-01

We have studied the effect of Mg doping on the surface kinetics of GaN during growth by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface of GaN, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN. The growth window is hence significantly reduced. Higher growth temperatures lead to an enhancement of Mg segregation and an improvement of the surface morphology

Thermal quenching of the yellow luminescence in GaN

Science.gov (United States)

Reshchikov, M. A.; Albarakati, N. M.; Monavarian, M.; Avrutin, V.; Morkoç, H.

2018-04-01

We observed varying thermal quenching behavior of the yellow luminescence band near 2.2 eV in different GaN samples. In spite of the different behavior, the yellow band in all the samples is caused by the same defect—the YL1 center. In conductive n-type GaN, the YL1 band quenches with exponential law, and the Arrhenius plot reveals an ionization energy of ˜0.9 eV for the YL1 center. In semi-insulating GaN, an abrupt and tunable quenching of the YL1 band is observed, where the apparent activation energy in the Arrhenius plot is not related to the ionization energy of the defect. In this case, the ionization energy can be found by analyzing the shift of the characteristic temperature of PL quenching with excitation intensity. We conclude that only one defect, namely, the YL1 center, is responsible for the yellow band in undoped and doped GaN samples grown by different techniques.

Mn doped GaN thin films and nanoparticles

Czech Academy of Sciences Publication Activity Database

Šofer, Z.; Sedmidubský, D.; Huber, Š.; Hejtmánek, Jiří; Macková, Anna; Fiala, R.

2012-01-01

Roč. 9, 8-9 (2012), s. 809-824 ISSN 1475-7435 R&D Projects: GA ČR GA104/09/0621 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10480505 Keywords : GaN nanoparticles * GaN thin films * manganese * transition metals * MOVPE * ion implantations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.087, year: 2012

Ion beam figuring of CVD silicon carbide mirrors

Science.gov (United States)

Gailly, P.; Collette, J.-P.; Fleury Frenette, K.; Jamar, C.

2017-11-01

Optical and structural elements made of silicon carbide are increasingly found in space instruments. Chemical vapor deposited silicon carbide (CVD-SiC) is used as a reflective coating on SiC optics in reason of its good behavior under polishing. The advantage of applying ion beam figuring (IBF) to CVD-SiC over other surface figure-improving techniques is discussed herein. The results of an IBF sequence performed at the Centre Spatial de Liège on a 100 mm CVD-SiC mirror are reported. The process allowed to reduce the mirror surface errors from 243 nm to 13 nm rms . Beside the surface figure, roughness is another critical feature to consider in order to preserve the optical quality of CVD-SiC . Thus, experiments focusing on the evolution of roughness were performed in various ion beam etching conditions. The roughness of samples etched at different depths down to 3 ≠m was determined with an optical profilometer. These measurements emphasize the importance of selecting the right combination of gas and beam energy to keep roughness at a low level. Kaufman-type ion sources are generally used to perform IBF but the performance of an end-Hall ion source in figuring CVD-SiC mirrors was also evaluated in this study. In order to do so, ion beam etching profiles obtained with the end-Hall source on CVD-SiC were measured and used as a basis for IBF simulations.

Defect formation and magnetic properties of Co-doped GaN crystal and nanowire

International Nuclear Information System (INIS)

Shi, Li-Bin; Liu, Jing-Jing; Fei, Ying

2013-01-01

Theoretical calculation based on density functional theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying defect formation and magnetic properties of Co doped GaN crystal and nanowire (NW). Co does not exhibit site preference in GaN crystal. However, Co occupies preferably surface sites in GaN NW. Transition level of the defect is also investigated in GaN crystal. We also find that Co Ga (S) in NW does not produce spin polarization and Co Ga (B) produces spontaneous spin polarization. Ferromagnetic (FM) and antiferromagnetic (AFM) couplings are analyzed by six different configurations. The results show that AFM coupling is more stable than FM coupling for Co doped GaN crystal. It is also found from Co doped GaN NW calculation that the system remains FM stability for majority of the configurations. Magnetic properties in Co doped GaN crystal can be mediated by N and Ga vacancies. The FM and AFM stability can be explained by Co 3d energy level coupling

Low-temperature graphene synthesis using microwave plasma CVD

International Nuclear Information System (INIS)

Yamada, Takatoshi; Kim, Jaeho; Ishihara, Masatou; Hasegawa, Masataka

2013-01-01

The graphene chemical vapour deposition (CVD) technique at substrate temperatures around 300 °C by a microwave plasma sustained by surface waves (surface wave plasma chemical vapour deposition, SWP-CVD) is discussed. A low-temperature, large-area and high-deposition-rate CVD process for graphene films was developed. It was found from Raman spectra that the deposited films on copper (Cu) substrates consisted of high-quality graphene flakes. The fabricated graphene transparent conductive electrode showed uniform optical transmittance and sheet resistance, which suggests the possibility of graphene for practical electrical and optoelectronic applications. It is intriguing that graphene was successfully deposited on aluminium (Al) substrates, for which we did not expect the catalytic effect to decompose hydrocarbon and hydrogen molecules. We developed a roll-to-roll SWP-CVD system for continuous graphene film deposition towards industrial mass production. A pair of winder and unwinder systems of Cu film was installed in the plasma CVD apparatus. Uniform Raman spectra were confirmed over the whole width of 297 mm of Cu films. We successfully transferred the deposited graphene onto PET films, and confirmed a transmittance of about 95% and a sheet resistance of less than 7 × 10 5 Ω/sq.

Low-temperature graphene synthesis using microwave plasma CVD

Science.gov (United States)

Yamada, Takatoshi; Kim, Jaeho; Ishihara, Masatou; Hasegawa, Masataka

2013-02-01

The graphene chemical vapour deposition (CVD) technique at substrate temperatures around 300 °C by a microwave plasma sustained by surface waves (surface wave plasma chemical vapour deposition, SWP-CVD) is discussed. A low-temperature, large-area and high-deposition-rate CVD process for graphene films was developed. It was found from Raman spectra that the deposited films on copper (Cu) substrates consisted of high-quality graphene flakes. The fabricated graphene transparent conductive electrode showed uniform optical transmittance and sheet resistance, which suggests the possibility of graphene for practical electrical and optoelectronic applications. It is intriguing that graphene was successfully deposited on aluminium (Al) substrates, for which we did not expect the catalytic effect to decompose hydrocarbon and hydrogen molecules. We developed a roll-to-roll SWP-CVD system for continuous graphene film deposition towards industrial mass production. A pair of winder and unwinder systems of Cu film was installed in the plasma CVD apparatus. Uniform Raman spectra were confirmed over the whole width of 297 mm of Cu films. We successfully transferred the deposited graphene onto PET films, and confirmed a transmittance of about 95% and a sheet resistance of less than 7 × 105 Ω/sq.

Chemical lift-off of (11-22) semipolar GaN using periodic triangular cavities

Science.gov (United States)

Jeon, Dae-Woo; Lee, Seung-Jae; Jeong, Tak; Baek, Jong Hyeob; Park, Jae-Woo; Jang, Lee-Woon; Kim, Myoung; Lee, In-Hwan; Ju, Jin-Woo

2012-01-01

Chemical lift-off of (11-22) semipolar GaN using triangular cavities was investigated. The (11-22) semipolar GaN was grown using epitaxial lateral overgrowth by metal-organic chemical vapor deposition on m-plane sapphire, in such a way as to keep N terminated surface of c-plane GaN exposed in the cavities. After regrowing 300 μm thick (11-22) semipolar GaN by hydride vapor phase epitaxy for a free-standing (11-22) semipolar GaN substrate, the triangular cavities of the templates were chemically etched in molten KOH. The (000-2) plane in the triangular cavities can be etched in the [0002] direction with the high lateral etching rate of 196 μm/min. The resulting free-standing (11-22) semipolar GaN substrate was confirmed to be strain-free by the Raman analysis.

Heteroepitaxial growth of basal plane stacking fault free a-plane GaN

Energy Technology Data Exchange (ETDEWEB)

Wieneke, Matthias; Hempel, Thomas; Noltemeyer, Martin; Witte, Hartmut; Dadgar, Armin; Blaesing, Juergen; Christen, Juergen; Krost, Alois [Otto-von-Guericke Universitaet Magdeburg, FNW/IEP, Magdeburg (Germany)

2010-07-01

Growth of light emitting quantum-wells based on a-plane GaN is a possibility to reduce or even to avoid polarization correlated luminescence red shift and reduction of radiative recombination efficiency. But until now heteroepitaxially grown a-plane GaN films are characterized by a poor crystalline quality expressed by a high density of basal plane stacking faults (BSF) and partial dislocations. We present Si doped a-plane GaN films grown on r-plane sapphire substrates by metal organic vapor phase epitaxy using high temperature AlGaN nucleation layers. FE-SEM images revealed three dimensionally grown GaN crystallites sized up to tenth micrometer in the basal plane and a few tenth micrometers along the c-axes. Though, the full width at half maxima of the X-ray diffraction {omega}-scans of the in-plane GaN(1 anti 100) and GaN(0002) Bragg reflections exhibited a very high crystal quality. Furthermore, luminescence spectra were dominated by near band gap emission, while there was no separated peak of the basal plane stacking fault. In summary we present heteroepitaxially grown a-plane GaN without an evidence of basal plane stacking faults in X-ray diffraction measurements and luminescence spectra.

Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

Science.gov (United States)

Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong; Zhao, Degang; Zhang, Baolin; Du, Guotong

2016-01-01

KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 ÿ 1017 cm⿿3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

The influence of Fe doping on the surface topography of GaN epitaxial material

International Nuclear Information System (INIS)

Cui Lei; Yin Haibo; Jiang Lijuan; Wang Quan; Feng Chun; Xiao Hongling; Wang Cuimei; Wang Xiaoliang; Gong Jiamin; Zhang Bo; Li Baiquan; Wang Zhanguo

2015-01-01

Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 10 19 cm −3 . High resistivity GaN epitaxial material which is 1 × 10 9 Ω·cm is achieved. (paper)

Lateral epitaxial overgrowth of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy

International Nuclear Information System (INIS)

Wang, Yongjin; Hu, Fangren; Hane, Kazuhiro

2011-01-01

We report here the lateral epitaxial overgrowth (LEO) of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy (MBE) growth with radio frequency nitrogen plasma as a gas source. Two kinds of GaN nanostructures are defined by electron beam lithography and realized on a GaN substrate by fast atom beam etching. The epitaxial growth of GaN by MBE is performed on the prepared GaN template, and the selective growth of GaN takes place with the assistance of GaN nanostructures. The LEO of GaN produces novel GaN epitaxial structures which are dependent on the shape and the size of the processed GaN nanostructures. Periodic GaN hexagonal pyramids are generated inside the air holes, and GaN epitaxial strips with triangular section are formed in the grating region. This work provides a promising way for producing novel GaN-based devices by the LEO of GaN using the MBE technique

Crystal Structures of GaN Nanodots by Nitrogen Plasma Treatment on Ga Metal Droplets

Directory of Open Access Journals (Sweden)

Yang-Zhe Su

2018-06-01

Full Text Available Gallium nitride (GaN is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111 by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiNx layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.

Fast method for reactor and feature scale coupling in ALD and CVD

Science.gov (United States)

Yanguas-Gil, Angel; Elam, Jeffrey W.

2017-08-08

Transport and surface chemistry of certain deposition techniques is modeled. Methods provide a model of the transport inside nanostructures as a single-particle discrete Markov chain process. This approach decouples the complexity of the surface chemistry from the transport model, thus allowing its application under general surface chemistry conditions, including atomic layer deposition (ALD) and chemical vapor deposition (CVD). Methods provide for determination of determine statistical information of the trajectory of individual molecules, such as the average interaction time or the number of wall collisions for molecules entering the nanostructures as well as to track the relative contributions to thin-film growth of different independent reaction pathways at each point of the feature.

Surface morphology of homoepitaxial GaN grown on non- and semipolar GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Wernicke, Tim; Hoffmann, Veit; Netzel, Carsten; Knauer, Arne; Weyers, Markus [FBH, Berlin (Germany); Ploch, Simon; Rass, Jens [Institute of Solid State Physics, TU Berlin (Germany); Schade, Lukas; Schwarz, Ulrich [IAF, Freiburg (Germany); Kneissl, Michael [FBH, Berlin (Germany); Institute of Solid State Physics, TU Berlin (Germany)

2010-07-01

Recently a number of groups have reported laser diodes in the green spectral range on semi- and nonpolar GaN. Nevertheless the growth process on semipolar surfaces is not well understood. In this study 3.5 {mu} m thick MOVPE grown GaN layers on bulk m-plane, (11 anti 22), (10 anti 12), and (10 anti 11) GaN substrates were investigated. XRD rocking curves exhibit a FWHM of less than 150{sup ''}, indicating excellent crystalline quality. But the surface morphology exhibits hillocks with a height of 1 {mu}m and lateral extension of 150 {mu}m in many cases. Depending on the substrate orientation and the growth temperature different hillock shapes were observed. Morphology and luminescence data point to threading dislocations as formation sources. In QWs the hillock structure is reproduced in the emission intensity and wavelength distribution on (10 anti 11) but not on the m-plane surfaces. The hillocks could be eliminated for the semipolar planes (not for the m-plane) by increasing the reactor pressure and lowering the growth temperature. Hillock free separate confinement laser structures emitting at 405 nm feature a very homogeneous luminescence in micro-PL and show amplified spontaneous emission under high power stripe excitation. Furthermore the In incorporation was found to be highest in QWs on (10 anti 11).

Optically active centers in Eu implanted, Eu in situ doped GaN, and Eu doped GaN quantum dots

International Nuclear Information System (INIS)

Bodiou, L.; Braud, A.; Doualan, J.-L.; Moncorge, R.; Park, J. H.; Munasinghe, C.; Steckl, A. J.; Lorenz, K.; Alves, E.; Daudin, B.

2009-01-01

A comparison is presented between Eu implanted and Eu in situ doped GaN thin films showing that two predominant Eu sites are optically active around 620 nm in both types of samples with below and above bandgap excitation. One of these sites, identified as a Ga substitutional site, is common to both types of Eu doped GaN samples despite the difference in the GaN film growth method and in the doping technique. High-resolution photoluminescence (PL) spectra under resonant excitation reveal that in all samples these two host-sensitized sites are in small amount compared to the majority of Eu ions which occupy isolated Ga substitutional sites and thus cannot be excited through the GaN host. The relative concentrations of the two predominant host-sensitized Eu sites are strongly affected by the annealing temperature for Eu implanted samples and by the group III element time opening in the molecular beam epitaxy growth. Red luminescence decay characteristics for the two Eu sites reveal different excitation paths. PL dynamics under above bandgap excitation indicate that Eu ions occupying a Ga substitutional site are either excited directly into the 5 D 0 level or into higher excited levels such as 5 D 1 , while Eu ions sitting in the other site are only directly excited into the 5 D 0 level. These differences are discussed in terms of the spectral overlap between the emission band of a nearby bound exciton and the absorption bands of Eu ions. The study of Eu doped GaN quantum dots reveals the existence of only one type of Eu site under above bandgap excitation, with Eu PL dynamics features similar to Eu ions in Ga substitutional sites

Infrared reflectance of GaN films grown on Si(001) substrates

International Nuclear Information System (INIS)

Zhang, Xiong; Hou, Yong-Tian; Feng, Zhe-Chuan; Chen, Jin-Li

2001-01-01

GaN thin films on Si(001) substrates are studied by infrared reflectance (IRR) spectroscopy at room temperature (RT). Variations in the IRR spectral line shape with the microstructure of GaN/Si(011) film are quantitatively explained in terms of a three-component effective medium model. In this model, the nominally undoped GaN film is considered to consist of three elementary components, i.e., single crystalline GaN grains, pores (voids), and inter-granulated materials (amorphous GaN clusters). Such a polycrystalline nature of the GaN/Si(001) films was confirmed by scanning electron microscopy measurements. It was demonstrated that based on the proposed three-component effective medium model, excellent overall simulation of the RT-IRR spectra can be achieved, and the fine structures of the GaN reststrahlen band in the measured RT-IRR spectra can also be interpreted very well. Furthermore, the volume fraction for each component in the GaN/Si(001) film was accurately determined by fitting the experimental RT-IRR spectra with the theoretical simulation. These results indicate that IRR spectroscopy can offer a sensitive and convenient tool to probe the microstructure of GaN films grown on silicon. [copyright] 2001 American Institute of Physics

Individual GaN nanowires exhibit strong piezoelectricity in 3D.

Science.gov (United States)

Minary-Jolandan, Majid; Bernal, Rodrigo A; Kuljanishvili, Irma; Parpoil, Victor; Espinosa, Horacio D

2012-02-08

Semiconductor GaN NWs are promising components in next generation nano- and optoelectronic systems. In addition to their direct band gap, they exhibit piezoelectricity, which renders them particularly attractive in energy harvesting applications for self-powered devices. Nanowires are often considered as one-dimensional nanostructures; however, the electromechanical coupling leads to a third rank tensor that for wurtzite crystals (GaN NWs) possesses three independent coefficients, d(33), d(13), and d(15). Therefore, the full piezoelectric characterization of individual GaN NWs requires application of electric fields in different directions and measurements of associated displacements on the order of several picometers. In this Letter, we present an experimental approach based on scanning probe microscopy to directly quantify the three-dimensional piezoelectric response of individual GaN NWs. Experimental results reveal that GaN NWs exhibit strong piezoelectricity in three dimensions, with up to six times the effect in bulk. Based on finite element modeling, this finding has major implication on the design of energy harvesting systems exhibiting unprecedented levels of power density production. The presented method is applicable to other piezoelectric NW materials as well as wires manufactured along different crystallographic orientations. © 2011 American Chemical Society

Characterization and growth mechanism of nonpolar and semipolar GaN layers grown on patterned sapphire substrates

International Nuclear Information System (INIS)

Okada, Narihito; Tadatomo, Kazuyuki

2012-01-01

Nonpolar and semipolar GaN layers with markedly improved crystalline quality can be obtained by selective-area growth from the sapphire sidewalls of patterned sapphire substrates (PSSs). In this paper, we review the crystalline qualities of GaN layers grown on PSSs and their growth mechanism. We grew semipolar {1 1 −2 2} and {1 0 −1 1} GaN layers on r- and n-PSSs. The crystalline qualities of the GaN layers grown on the PSSs were higher than those of GaN layers grown directly on heteroepitaxial substrates. To reveal the growth mechanism of GaN layers grown on PSSs, we also grew various nonpolar and semipolar GaN layers such as m-GaN on a-PSS, {1 1 −2 2} GaN on r-PSS, {1 0 − 1  1} GaN on n-PSS, m-GaN on c-PSS and a-GaN on m-PSS. It was found that the nucleation of GaN on the c-plane-like sapphire sidewall results in selective growth from the sapphire sidewall, and nonpolar or semipolar GaN can be obtained. Finally, we demonstrated a light-emitting diode fabricated on a {1 1 −2 2} GaN layer grown on an r-PSS. (paper)

N-polar GaN epitaxy and high electron mobility transistors

International Nuclear Information System (INIS)

Wong, Man Hoi; Keller, Stacia; Dasgupta, Nidhi Sansaptak; Denninghoff, Daniel J; Kolluri, Seshadri; Brown, David F; Lu, Jing; Fichtenbaum, Nicholas A; Ahmadi, Elaheh; DenBaars, Steven P; Speck, James S; Mishra, Umesh K; Singisetti, Uttam; Chini, Alessandro; Rajan, Siddharth

2013-01-01

This paper reviews the progress of N-polar (0001-bar) GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion- and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized. (invited review)

Chemical vapor deposition of tantalum on graphite cloth for making hot pressed fiber reinforced carbide-graphite composite

International Nuclear Information System (INIS)

Hollabaugh, C.M.; Davidson, K.V.; Radosevich, C.L.; Riley, R.E.; Wallace, T.C.

1977-01-01

Conditions for the CVD of a uniform coating of Ta on fibers of a woven graphite cloth were established. The effect of gas composition, pressure, and temperature were investigated, and the conditions that gave the desired results are presented. Several layers of the coated cloth were hot pressed to produce a TaC--C composite having uniformly dispersed, fine-grained TaC in graphite. Three compositions were hot pressed: 15, 25, and 40 volume percent carbide. 8 figures, 2 tables

Structural effects of field emission from GaN nanofilms on SiC substrates

Energy Technology Data Exchange (ETDEWEB)

Chen, Cheng-Cheng; Wang, Ru-Zhi, E-mail: wrz@bjut.edu.cn; Zhu, Man-Kang; Yan, Hui [College of Materials Science and Engineering, Beijing University of Technology, 100 Pingleyuan, Chaoyang District, Beijing 100124 (China); Liu, Peng [Department of Physics Tsinghua University, Tsinghua-Foxconn Nanotechnology Research Center, Beijing 100084 (China); Wang, Bi-Ben [College of Chemistry and Chemical Engineering, Chongqing University of Technology, Chongqing 400054 (China)

2014-04-21

GaN nanofilms (NFs) with different structures are grown on SiC substrates by pulsed laser deposition under different conditions. The synthesized GaN NFs are studied by X-ray diffraction, field-emission (FE) scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GaN NFs are composed of diversified GaN nanoparticles with a diameter of 9–38 nm, thickness of 10–50 nm, and roughness of 0.22–13.03 nm. FE from the GaN NFs is structure dependent, which is explained by stress changing the band gap of the NFs. By structure modulation, the turn-on field of GaN NFs can be as low as 0.66 V/μm at a current density of 1 μA/cm{sup 2}, with a current density of up to 1.1 mA/cm{sup 2} at a field of 4.18 V/μm. Fowler-Nordheim curves of some samples contain multiple straight lines, which originate from the structural change and diversification of GaN nanoparticles under an applied field. Overall, our results suggest that GaN NFs with excellent FE properties can be prepared on SiC substrates, which provides a new route to fabricate high-efficiency FE nanodevices.

Polarity-inverted lateral overgrowth and selective wet-etching and regrowth (PILOSWER) of GaN.

Science.gov (United States)

Jang, Dongsoo; Jue, Miyeon; Kim, Donghoi; Kim, Hwa Seob; Lee, Hyunkyu; Kim, Chinkyo

2018-03-07

On an SiO 2 -patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H 3 PO 4 , this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO 2 -patterned sapphire.

Amphoteric arsenic in GaN

CERN Document Server

Wahl, U; Araújo, J P; Rita, E; Soares, JC

2007-01-01

We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\\scriptstyle_{Ga}\\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\\scriptstyle_{1-x}$N$\\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.

Polarity analysis of GaN nanorods by photo-assisted Kelvin probe force microscopy

Energy Technology Data Exchange (ETDEWEB)

Wei, Jiandong; Neumann, Richard; Wang, Xue; Li, Shunfeng; Fuendling, Soenke; Merzsch, Stephan; Al-Suleiman, Mohamed A.M.; Soekmen, Uensal; Wehmann, Hergo-H.; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig (Germany)

2011-07-15

Polarity dependence (N-polar (000-1) and Ga-polar (0001)) of surface photovoltage of epitaxially grown, vertically aligned GaN nanorods has been investigated by photo-assisted Kelvin probe force microscopy (KPFM). Commercial GaN substrates with known polarities are taken as reference samples. The polarity of GaN substrates can be well distinguished by the change in surface photovoltage upon UV illumination in air ambient. These different behaviors of Ga- and N-polar surfaces are attributed to the polarity-related surface-bound charges and photochemical reactivity. GaN nanorods were grown on patterned SiO{sub 2}/sapphire templates by metal-organic vapor phase epitaxy (MOVPE). In order to analyze the bottom surface of the grown GaN nanorods, a technique known from high power electronics and joining techniques is applied to remove the substrate. The top and bottom surfaces of the GaN nanorods are identified to be N-polar and Ga-polar according to the KPFM results, respectively. Our experiments demonstrate that KPFM is a simple and suitable method capable to identify the polarity of GaN nanorods. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Stage of GAN (Grupo de Analise do Nucleo) calculus methodology

International Nuclear Information System (INIS)

Silva, C.F. da.

1987-11-01

This Technical Note presents the stage of GAN Calculus Methodology in areas of Neutronics, Fuel Rod Performance and Fission Products Inventory. Proposals of GAN's members are presented and analyzed for each of these areas and a work schedule is established. (author)

Rare earths in GaN and ZnO studied with the PAC method; Seltene Erden in GaN und ZnO untersucht mit der PAC-Methode

Energy Technology Data Exchange (ETDEWEB)

Nedelec, R.

2007-07-01

The present thesis deals with the implantation and annealing behaviour of two examples of large-band-gap semiconductors GaN and ZnO. The studies begin with the annealing behaviour of GaN after the implantation of {sup 172}Lu. For GaN the annealing process begins at low temperatures with the decreasing of the damping of the lattice frequency. At essentially higher temperatures finally the substitunial contribution increases. This behaviour is also observed for other probe nuclei in GaN. For ZnO the behaviour at low temperature is different. Both for {sup 172}Lu and for {sup 181}Hf the damping is already after the implantation very low. The increasement of the substitutional contribution occurs like in GaN at higher temperatures. Thereafter for GaN and ZnO PAC spectra were token up at different measurement temperatures between 25 and 873 K. For {sup 172}Lu in GaN and in ZnO a strong temperature dependence of the lattice field gradient was observed. Also for {sup 181}Hf in ZnO a strong temperature dependence is observed. For {sup 172}Lu by means of a model for the interaction of quadrupole moments of electronic shells with the nucleus a lattice field gradient of {+-}5.9.10{sup 15} Vcm{sup -2} could be determined. For {sup 172}Lu in ZnO the model yields at 293 K a lattice field gradient of +14.10{sup 15} Vcm{sup -2} respectively -13.10{sup 15} Vcm{sup -2}. The corrsponding measurement with {sup 181}Hf yields a lattice field gradient of {+-}5.7.10{sup 15} Vcm{sup -2}.

Design and simulation of GaN based Schottky betavoltaic nuclear micro-battery

International Nuclear Information System (INIS)

San, Haisheng; Yao, Shulin; Wang, Xiang; Cheng, Zaijun; Chen, Xuyuan

2013-01-01

The current paper presents a theoretical analysis of Ni-63 nuclear micro-battery based on a wide-band gap semiconductor GaN thin-film covered with thin Ni/Au films to form Schottky barrier for carrier separation. The total energy deposition in GaN was calculated using Monte Carlo methods by taking into account the full beta spectral energy, which provided an optimal design on Schottky barrier width. The calculated results show that an 8 μm thick Schottky barrier can collect about 95% of the incident beta particle energy. Considering the actual limitations of current GaN growth technique, a Fe-doped compensation technique by MOCVD method can be used to realize the n-type GaN with a carrier concentration of 1×10 15 cm −3 , by which a GaN based Schottky betavoltaic micro-battery can achieve an energy conversion efficiency of 2.25% based on the theoretical calculations of semiconductor device physics. - Highlights: • Ni-63 is employed as the pure beta radioisotope source. • The Schottky junction betavoltaic battery is based on the wide-band gap semiconductor GaN. • The total energy deposition of incident beta particles in GaN was simulated by the Monte Carlo method. • A Fe-doped compensation technique is suggested to increase the energy conversion efficiency

Test of radiation hardness of pcCVD detectors

Energy Technology Data Exchange (ETDEWEB)

Schlemme, Steffen [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany); Technische Universitaet Darmstadt (Germany); Enders, Joachim [Technische Universitaet Darmstadt (Germany); Figuera, P.; Salamone, S. [LNS-INFN Catania (Italy); Fruehauf, J.; Kis, Mladen; Kratz, A.; Kurz, N.; Loechner, S.; Nociforo, Chiara; Schirru, Fabio; Szczepanczyk, B.; Traeger, M.; Visinka, R. [GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany); Musumarra, A. [LNS-INFN Catania (Italy); University of Catania (Italy)

2016-07-01

The new in-flight separator Super-FRS is under construction at the Facility for Antiproton and Ion Research (FAIR, Darmstadt). Ion rates up to 3 x 10{sup 11} {sup 238}U/spill demand an adaption of detectors to a high radiation environment. A test experiment to investigate the radiation hardness of polycrystalline diamond detectors (pcCVD) was performed at the LNS-INFN in Catania using a {sup 12}C beam at 62 MeV/u and intensities of up to 1.5 pnA. The setup consisted of pcCVD strip detectors to measure the beam profile, a single crystal diamond detector to calibrate the ionisation chamber working in current mode as a beam intensity monitor and a pcCVD sample to be irradiated. The IC used was designed for FAIR and showed a stable counting rate allowing us to calibrate and perform beam intensity measurements with it. The total measured counts on the sample were 8.25 x 10{sup 11} counts/mm{sup 2} over a period of 60 hours. Digital waveforms of the pcCVD signals were taken with an oscilloscope and analysed. The results showed no change of the pcCVD signal properties during the entire irradiation.

Characterization of wall conditions in DIII-D

International Nuclear Information System (INIS)

Holtrop, K.L.; Jackson, G.L.; Kellman, A.G.; Lee, R.L.; West, W.P.; Wood, R.D.; Whyte, D.G.

1996-10-01

Wall conditioning in DIII-D is one of the most important factors in achieving reproducible high confinement discharges. For example, the very high confinement mode (VH-mode) was only discovered after boronization, a CVD technique to deposit a thin boron film over the entire surface of the tokamak. In order to evaluate wall conditions and provide a data base to correlate these wall conditions with tokamak discharge performance, a series of nominally identical reference VH-mode discharges (1.6 MA, 2.1 T, double-null diverted) were taken at various times during a series of experimental campaigns with evolving wall conditions. These reference discharges have allowed a quantitative determination of how the wall conditions have evolved. For instance, core carbon and oxygen levels in the VH-mode phase remains at historically low levels during the 1995 run year and there was also a steady decrease in the oxygen levels at plasma initiation during this period. The authors discuss the long term changes in low Z impurities and the effect of wall conditioning techniques such as boronization and baking on these impurities. In addition, the evolution of the deuterium recycling rates will be discussed

Photoconductive GaN UV Detectors

National Research Council Canada - National Science Library

Baranowski, Jacek

1999-01-01

This report results from a contract tasking University of Warsaw as follows: The contractor will investigate the growth of GaN material using atmospheric pressure metalorganic chemical vapor deposition method (MOCVD...

Thermogravimetric analysis and TEM characterization of the oxidation and defect sites of carbon nanotubes synthesized by CVD of methane

International Nuclear Information System (INIS)

Li Haipeng; Zhao Naiqin; He Chunnian; Shi Chunsheng; Du Xiwen; Li Jiajun

2008-01-01

Changes in the thermogravimetrically determined oxidation behaviors of CVD-grown multi-walled carbon nanotubes (MWNTs) over Ni/Al catalyst with different Ni content were examined. Catalyst type was found to have a measurable impact upon nanotube stability, suggesting differing levels of crystalline perfection in the resulting nanotubes. With increasing the Ni content in the Ni/Al catalyst, the CNTs obtained became less stable during heat treatment in air. Furthermore, high-resolution transmission electron microscopy was employed to investigate the defect sites of as-grown MWNTs. The results provide evidence showing that defect sites along the walls and at the ends of the raw MWNTs facilitate the thermal oxidative destruction of the nanotubes

Impact of substrate off-angle on the m-plane GaN Schottky diodes

Science.gov (United States)

Yamada, Hisashi; Chonan, Hiroshi; Takahashi, Tokio; Shimizu, Mitsuaki

2018-04-01

We investigated the effects of the substrate off-angle on the m-plane GaN Schottky diodes. GaN epitaxial layers were grown by metal-organic chemical vapor deposition on m-plane GaN substrates having an off-angle of 0.1, 1.1, 1.7, or 5.1° toward [000\\bar{1}]. The surface of the GaN epitaxial layers on the 0.1°-off substrate consisted of pyramidal hillocks and contained oxygen (>1017 cm-3) and carbon (>1016 cm-3) impurities. The residual carbon and oxygen impurities decreased to current of the 0.1°-off m-plane GaN Schottky diodes originated from the +c facet of the pyramidal hillocks. The leakage current was efficiently suppressed through the use of an off-angle that was observed to be greater than 1.1°. The off-angle of the m-plane GaN substrate is critical in obtaining high-performance Schottky diodes.

MOCVD growth of GaN layer on InN interlayer and relaxation of residual strain

Energy Technology Data Exchange (ETDEWEB)

Lee, Keon-Hun; Park, Sung Hyun; Kim, Jong Hack; Kim, Nam Hyuk; Kim, Min Hwa [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Na, Hyunseok [Department of Advanced Materials Science and Engineering, Daejin University, Pocheon, 487-711 (Korea, Republic of); Yoon, Euijoon, E-mail: eyoon@snu.ac.k [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, Suwon 433-270 (Korea, Republic of)

2010-09-01

100 nm InN layer was grown on sapphire c-plane using a metal-organic chemical vapor deposition (MOCVD) system. Low temperature (LT) GaN layer was grown on InN layer to protect InN layer from direct exposure to hydrogen flow during high temperature (HT) GaN growth and/or abrupt decomposition. Subsequently, thick HT GaN layer (2.5 {mu}m thick) was grown at 1000 {sup o}C on LT GaN/InN/sapphire template. Microstructure of epilayer-substrate interface was investigated by transmission electron microscopy (TEM). From the high angle annular dark field TEM image, the growth of columnar structured LT GaN and HT GaN with good crystallinity was observed. Though thickness of InN interlayer is assumed to be about 100 nm based on growth rate, it was not clearly shown in TEM image due to the InN decomposition. The lattice parameters of GaN layers were measured by XRD measurement, which shows that InN interlayer reduces the compressive strain in GaN layer. The relaxation of compressive strain in GaN layer was also confirmed by photoluminescence (PL) measurement. As shown in the PL spectra, red shift of GaN band edge peak was observed, which indicates the reduction of compressive strain in GaN epilayer.

Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

International Nuclear Information System (INIS)

Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

2014-01-01

One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis

Fabrication of GaN epitaxial thin film on InGaZnO4 single-crystalline buffer layer

International Nuclear Information System (INIS)

Shinozaki, Tomomasa; Nomura, Kenji; Katase, Takayoshi; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo

2010-01-01

Epitaxial (0001) films of GaN were grown on (111) YSZ substrates using single-crystalline InGaZnO 4 (sc-IGZO) lattice-matched buffer layers by molecular beam epitaxy with a NH 3 source. The epitaxial relationships are (0001) GaN //(0001) IGZO //(111) YSZ in out-of-plane and [112-bar 0] GaN //[112-bar 0] IGZO //[11-bar 0] YSZ in in-plane. This is different from those reported for GaN on many oxide crystals; the in-plane orientation of GaN crystal lattice is rotated by 30 o with respect to those of oxide substrates except for ZnO. Although these GaN films showed relatively large tilting and twisting angles, which would be due to the reaction between GaN and IGZO, the GaN films grown on the sc-IGZO buffer layers exhibited stronger band-edge photoluminescence than GaN grown on a low-temperature GaN buffer layer.

Fabrication and Characterization of Mg-Doped GaN Nanowires

International Nuclear Information System (INIS)

Dong-Dong, Zhang; Cheng-Shan, Xue; Hui-Zhao, Zhuang; Ying-Long, Huang; Zou-Ping, Wang; Ying, Wang; Yong-Fu, Guo

2008-01-01

Mg-doped GaN nanowires have been synthesized by ammoniating Ga 2 O 3 films doped with Mg under flowing ammonia atmosphere at 850° C. The Mg-doped GaN nanowires are characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photo-luminescence (PL). The results demonstrate that the nanowires are single crystalline with hexagonal wurzite structure. The diameters of the nanowires are 20–30 nm and the lengths are 50–100 μm. The GaN nanowires show three emission bands with well-defined PL peak at 3.45 eV, 3.26 eV, 2.95 eV, respectively. The large distinct blueshift of the bandgap emission can be attributed to the Burstein–Moss effect. The peak at 3.26 eV represents the transition from the conduction-band edge to the acceptor level AM (acceptor Mg). The growth mechanism of crystalline GaN nanowires is discussed briefly. (cross-disciplinary physics and related areas of science and technology)

Synthesis of γ-WO{sub 3} thin films by hot wire-CVD and investigation of its humidity sensing properties

Energy Technology Data Exchange (ETDEWEB)

Jadkar, Vijaya; Waykar, Ravindra; Jadhavar, Ashok [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Pawbake, Amit [School of Energy Studies, Savitribai Phule Pune University, Pune 411 007 (India); Physical and Material Chemistry Division, National Chemical Laboratory, Pune 411 008 (India); Date, Abhijit [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Plenty Road, Bundoora, Melbourne VIC 3083 (Australia); Late, Dattatray [Physical and Material Chemistry Division, National Chemical Laboratory, Pune 411 008 (India); Pathan, Habib; Gosavi, Suresh; Jadkar, Sandesh [Department of Physics, Savitribai Phule Pune University, Pune 411 007 (India)

2017-05-15

In this study, monoclinic tungsten oxide (γ-WO{sub 3}) have been grown in a single step using HW-CVD method by resistively heating W filaments in a constant O{sub 2} pressure. The formation of γ-WO{sub 3} was confirmed using low angle-XRD and Raman spectroscopy analysis. Low angle-XRD analysis revealed that as-deposited WO{sub 3} film are highly crystalline and the crystallites have preferred orientation along the (002) direction. HRTEM analysis and SAED pattern also show the highly crystalline nature of WO{sub 3} with d spacing of ∝ 0.38 nm, having an orientation along the (002) direction. Surface topography investigated by SEM analysis shows the formation of a uniform and homogeneous cauliflower like morphology throughout the substrate surface without flaws and cracks. A humidity sensing device incorporating WO{sub 3} is also fabricated, which shows a maximum humidity sensitivity factor of ∝ 3954% along with a response time of ∝14 s and a recovery time of ∝25 s. The obtained results demonstrate that it is possible to synthesize WO{sub 3} in a single step by HW-CVD method and to fabricate a humidity sensor by using it. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Influence of ammonia flow rate for improving properties of polycrystalline GaN

Science.gov (United States)

Ariff, A.; Ahmad, M. A.; Hassan, Z.; Zainal, N.

2018-06-01

Post-annealing treatment in ammonia ambient is widely accepted for GaN material, but less works have been done to investigate the influence of the ammonia (NH3) flow rate for reducing the N-deficiency as well as improving the quality of the material. In this work, we investigated the influence of NH3 flow rate at 1, 2, 3, and 4 slm in improving properties of a ∼1 μm thick polycrystalline GaN layer. Our simulation work suggested that the uniformity of temperature and pressure gradient of the NH3 gas did not lead to the reduction of N-deficiency of the polycrystalline GaN layer. Instead, it was found that the mitigation of the N-deficiency was strongly influenced by the fluid velocity of the NH3 gas, which had passed over the layer. Either at lower or higher fluid velocity, the chance for the active N atoms to incorporate into the GaN lattice structure was low. Therefore, the N-deficiency on the polycrystalline GaN layer could not be minimized under these conditions. As measured by EDX, the N atoms incorporation was the most effective when the NH3 flow rate at 3 slm, suggesting the flow rate significantly improved the N-deficiency of the polycrystalline GaN layer. Furthermore, it favored the formation of larger hexagonal faceted grains, with the smallest FWHM of XRD peaks from the GaN diffractions in (10 1 bar 0), (0002) and (10 1 bar 1) orientations, while allowing the polycrystalline GaN layer to show sharp and intense emissions peak of NBE in a PL spectrum.

Ab initio-based approach to reconstruction, adsorption and incorporation on GaN surfaces

International Nuclear Information System (INIS)

Ito, T; Akiyama, T; Nakamura, K

2012-01-01

Reconstruction, adsorption and incorporation on various GaN surfaces are systematically investigated using an ab initio-based approach that predicts the surface phase diagram as functions of temperature and beam-equivalent pressure (BEP). The calculated results for GaN surface reconstructions with polar (0 0 0 1), nonpolar (1 1 −2 0), semipolar (1 −1 0 1) and semipolar (1 1 −2 2) orientations imply that reconstructions on GaN surfaces with Ga adlayers generally appear on the polar and the semipolar surfaces, while the stable ideal surface without Ga adsorption is found on the nonpolar GaN(1 1 −2 0) surface because it satisfies the electron counting rule. The hydrogen adsorption on GaN(0 0 0 1) and GaN(1 1 −2 0) realizes several surface structures forming N–H and Ga–NH 2 bonds on their surfaces that depend on temperature and Ga BEP during metal-organic vapor-phase epitaxy (MOVPE). In contrast, the stable structures due to hydrogen adsorption on the semipolar GaN(1 −1 0 1) and GaN(1 1 −2 2) surfaces are not varied over the wide range of temperature and Ga BEP. This implies that the hydrogen adsorbed stable structures are expected to emerge on the semipolar surfaces during MOVPE regardless of the growth conditions. Furthermore, we clarify that Mg incorporation on GaN(1 −1 0 1) surfaces is enhanced by hydrogen adsorption consistent with experimental findings

The investigation of stress in freestanding GaN crystals grown from Si substrates by HVPE.

Science.gov (United States)

Lee, Moonsang; Mikulik, Dmitry; Yang, Mino; Park, Sungsoo

2017-08-17

We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.

High-electron-mobility GaN grown on free-standing GaN templates by ammonia-based molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Kyle, Erin C. H., E-mail: erinkyle@umail.ucsb.edu; Kaun, Stephen W.; Burke, Peter G.; Wu, Feng; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Wu, Yuh-Renn [Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei City 10617, Taiwan (China)

2014-05-21

The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n{sup −}-GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2 × 10{sup 6} cm{sup −2} to ∼2 × 10{sup 10} cm{sup −2}) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimized GaN growth on free-standing GaN templates with a low TDD (∼2 × 10{sup 6} cm{sup −2}) resulted in electron mobilities of 1265 cm{sup 2}/Vs at 296 K and 3327 cm{sup 2}/Vs at 113 K.

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si.

Science.gov (United States)

Tanaka, Atsunori; Choi, Woojin; Chen, Renjie; Dayeh, Shadi A

2017-10-01

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain-relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN-on-Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack-free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 7 cm -2 achieved to date in GaN-on-Si is demonstrated. With these advances, the first vertical GaN metal-insulator-semiconductor field-effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost-effective high power device paradigm on an Si CMOS platform are demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective area growth of GaN rod structures by MOVPE: Dependence on growth conditions

Energy Technology Data Exchange (ETDEWEB)

Li, Shunfeng; Fuendling, Soenke; Wang, Xue; Erenburg, Milena; Al-Suleiman, Mohamed Aid Mansur; Wei, Jiandong; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Bergbauer, Werner [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Osram Opto Semiconductors GmbH, Leibnizstr. 4, 93055 Regensburg (Germany); Strassburg, Martin [Osram Opto Semiconductors GmbH, Leibnizstr. 4, 93055 Regensburg (Germany)

2011-07-15

Selective area growth of GaN nanorods by metalorganic vapor phase epitaxy is highly demanding for novel applications in nano-optoelectronic and nanophotonics. Recently, we report the successful selective area growth of GaN nanorods in a continuous-flow mode. In this work, as examples, we show the morphology dependence of GaN rods with {mu}m or sub-{mu}m in diameters on growth conditions. Firstly, we found that the nitridation time is critical for the growth, with an optimum from 90 to 180 seconds. This leads to more homogeneous N-polar GaN rods growth. A higher temperature during GaN rod growth tends to increase the aspect ratio of the GaN rods. This is due to the enhanced surface diffusion of growth species. The V/III ratio is also an important parameter for the GaN rod growth. Its increase causes reduction of the aspect ratio of GaN rods, which could be explained by the relatively lower growth rate on (000-1) N-polar top surface than it on {l_brace}1-100{r_brace} m-planes by supplying more NH{sub 3} (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Luminescence evolution of porous GaN thin films prepared via UV-assisted electrochemical etching

International Nuclear Information System (INIS)

Cheah, S.F.; Lee, S.C.; Ng, S.S.; Yam, F.K.; Abu Hassan, H.; Hassan, Z.

2015-01-01

Porous gallium nitride (GaN) thin films with different surface morphologies and free carriers properties were fabricated from Si-doped GaN thin films using ultra-violet assisted electrochemical etching approach under various etching voltages. Fluctuation of luminescence signals was observed in the photoluminescence spectra of porous GaN thin films. Taking advantage of the spectral sensitivity of infrared attenuated total reflection spectroscopy on semiconductor materials, roles of free carriers and porous structure in controlling luminescence properties of GaN were investigated thoroughly. The results revealed that enhancement in luminescence signal is not always attained upon porosification. Although porosification is correlated to the luminescence enhancement, however, free carrier is the primary factor to enhance luminescence intensity. Due to unavoidable significant reduction of free carriers from Si-doped GaN in the porosification process, control of etching depth (i.e., thickness of porous layer formed from the Si-doped layer) is critical in fabricating porous GaN thin film with enhanced luminescence response. - Highlights: • Various pore morphologies with free carrier properties are produced by Si-doped GaN. • Free carriers are important to control the luminescence signal of porous GaN. • Enhancement of luminescence signal relies on the pore depth of Si-doped layer

Oxygen adsorption and incorporation at irradiated GaN(0001) and GaN(0001¯) surfaces: First-principles density-functional calculations

Science.gov (United States)

Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

2006-11-01

Density functional theory calculations of oxygen adsorption and incorporation at the polar GaN(0001) and GaN(0001¯) surfaces have been carried out to explain the experimentally observed reduced oxygen concentration in GaN samples grown by molecular beam epitaxy in the presence of high energy (˜10keV) electron beam irradiation [Myers , J. Vac. Sci. Technol. B 18, 2295 (2000)]. Using a model in which the effect of the irradiation is to excite electrons from the valence to the conduction band, we find that both the energy cost of incorporating oxygen impurities in deeper layers and the oxygen adatom diffusion barriers are significantly reduced in the presence of the excitation. The latter effect leads to a higher probability for two O adatoms to recombine and desorb, and thus to a reduced oxygen concentration in the irradiated samples, consistent with experimental observations.

Macrodefect-free, large, and thick GaN bulk crystals for high-quality 2–6 in. GaN substrates by hydride vapor phase epitaxy with hardness control

Science.gov (United States)

Fujikura, Hajime; Konno, Taichiro; Suzuki, Takayuki; Kitamura, Toshio; Fujimoto, Tetsuji; Yoshida, Takehiro

2018-06-01

On the basis of a novel crystal hardness control, we successfully realized macrodefect-free, large (2–6 in.) and thick +c-oriented GaN bulk crystals by hydride vapor phase epitaxy. Without the hardness control, the introduction of macrodefects including inversion domains and/or basal-plane dislocations seemed to be indispensable to avoid crystal fracture in GaN growth with millimeter thickness. However, the presence of these macrodefects tended to limit the applicability of the GaN substrate to practical devices. The present technology markedly increased the GaN crystal hardness from below 20 to 22 GPa, thus increasing the available growth thickness from below 1 mm to over 6 mm even without macrodefect introduction. The 2 and 4 in. GaN wafers fabricated from these crystals had extremely low dislocation densities in the low- to mid-105 cm‑2 range and low off-angle variations (2 in.: <0.1° 4 in.: ∼0.2°). The realization of such high-quality 6 in. wafers is also expected.

Growth and characterization of semi-insulating carbon-doped/undoped GaN multiple-layer buffer

International Nuclear Information System (INIS)

Kim, Dong-Seok; Won, Chul-Ho; Kang, Hee-Sung; Kim, Young-Jo; Kang, In Man; Lee, Jung-Hee; Kim, Yong Tae

2015-01-01

We have proposed a new semi-insulating GaN buffer layer, which consists of multiple carbon-doped and undoped GaN layer. The buffer layer showed sufficiently good semi-insulating characteristics, attributed to the depletion effect between the carbon-doped GaN and the undoped GaN layers, even though the thickness of the carbon-doped GaN layer in the periodic structure was designed to be very thin to minimize the total carbon incorporation into the buffer layer. The AlGaN/AlN/GaN heterostructure grown on the proposed buffer exhibited much better electrical and structural properties than that grown on the conventional thick carbon-doped semi-insulating GaN buffer layer, confirmed by Hall measurement, x-ray diffraction, and secondary ion mass spectrometry. The fabricated device also showed excellent buffer breakdown characteristics. (paper)

Ion Beam Assisted Deposition of Thin Epitaxial GaN Films.

Science.gov (United States)

Rauschenbach, Bernd; Lotnyk, Andriy; Neumann, Lena; Poppitz, David; Gerlach, Jürgen W

2017-06-23

The assistance of thin film deposition with low-energy ion bombardment influences their final properties significantly. Especially, the application of so-called hyperthermal ions (energy GaN thin films on (0001)-oriented 6H-SiC substrates at 700 °C. The films are studied in situ by reflection high energy electron diffraction, ex situ by X-ray diffraction, scanning tunnelling microscopy, and high-resolution transmission electron microscopy. It is demonstrated that the film growth mode can be controlled by varying the ion to atom ratio, where 2D films are characterized by a smooth topography, a high crystalline quality, low biaxial stress, and low defect density. Typical structural defects in the GaN thin films were identified as basal plane stacking faults, low-angle grain boundaries forming between w-GaN and z-GaN and twin boundaries. The misfit strain between the GaN thin films and substrates is relieved by the generation of edge dislocations in the first and second monolayers of GaN thin films and of misfit interfacial dislocations. It can be demonstrated that the low-energy nitrogen ion assisted molecular beam epitaxy is a technique to produce thin GaN films of high crystalline quality.

Nanoscale imaging of surface piezoresponse on GaN epitaxial layers

International Nuclear Information System (INIS)

Stoica, T.; Calarco, R.; Meijers, R.; Lueth, H.

2007-01-01

Surfaces of GaN films were investigated by atomic force microscopy (AFM) with implemented piezoelectric force microscopy technique. A model of PFM based on the surface depletion region in GaN films is discussed. The local piezoelectric effect of the low frequency regime was found to be in phase with the applied voltage on large domains, corresponding to a Ga-face of the GaN layer. Low piezoresponse is obtained within the inter-domain regions. The use of frequencies near a resonance frequency enhances very much the resolution of piezo-imaging, but only for very low scanning speed the piezo-imaging can follow the local piezoelectric effect. An inversion of the PFM image contrast is obtained for frequencies higher than the resonance frequencies. The effect of a chemical surface treatment on the topography and the piezoresponse of the GaN films was also investigated. Textured surfaces with very small domains were observed after the chemical treatment. For this kind of surfaces, piezo-induced torsion rather than bending of the AFM cantilever dominates the contrast of the PFM images. A small memory effect was observed, and explained by surface charging and confinement of the piezoelectric effect within the carrier depletion region at the GaN surface

A CVD diamond beam telescope for charged particle tracking

CERN Document Server

Adam, W; Bergonzo, P; de Boer, Wim; Bogani, F; Borchi, E; Brambilla, A; Bruzzi, Mara; Colledani, C; Conway, J; D'Angelo, P; Dabrowski, W; Delpierre, P A; Dulinski, W; Doroshenko, J; Doucet, M; van Eijk, B; Fallou, A; Fischer, P; Fizzotti, F; Kania, D R; Gan, K K; Grigoriev, E; Hallewell, G D; Han, S; Hartjes, F G; Hrubec, Josef; Husson, D; Kagan, H; Kaplon, J; Kass, R; Keil, M; Knöpfle, K T; Koeth, T W; Krammer, Manfred; Meuser, S; Lo Giudice, A; MacLynne, L; Manfredotti, C; Meier, D; Menichelli, D; Mishina, M; Moroni, L; Noomen, J; Oh, A; Pan, L S; Pernicka, Manfred; Perera, L P; Riester, J L; Roe, S; Rudge, A; Russ, J; Sala, S; Sampietro, M; Schnetzer, S; Sciortino, S; Stelzer, H; Stone, R; Suter, B; Trischuk, W; Tromson, D; Vittone, E; Weilhammer, Peter; Wermes, N; Wetstein, M; Zeuner, W; Zöller, M

2002-01-01

CVD diamond is a radiation hard sensor material which may be used for charged particle tracking near the interaction region in experiments at high luminosity colliders. The goal of the work described here is to investigate the use of several detector planes made of CVD diamond strip sensors for charged particle tracking. Towards this end a tracking telescope composed entirely of CVD diamond planes has been constructed. The telescope was tested in muon beams and its tracking capability has been investigated.

Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

International Nuclear Information System (INIS)

De-Gang, Zhao; Shuang, Zhang; Wen-Bao, Liu; De-Sheng, Jiang; Jian-Jun, Zhu; Zong-Shun, Liu; Hui, Wang; Shu-Ming, Zhang; Hui, Yang; Xiao-Peng, Hao; Long, Wei

2010-01-01

The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Verification of thermo-fluidic CVD reactor model

International Nuclear Information System (INIS)

Lisik, Z; Turczynski, M; Ruta, L; Raj, E

2014-01-01

Presented paper describes the numerical model of CVD (Chemical Vapour Deposition) reactor created in ANSYS CFX, whose main purpose is the evaluation of numerical approaches used to modelling of heat and mass transfer inside the reactor chamber. Verification of the worked out CVD model has been conducted with measurements under various thermal, pressure and gas flow rate conditions. Good agreement between experimental and numerical results confirms correctness of the elaborated model.

Control of strain in GaN by a combination of H2 and N2 carrier gases

International Nuclear Information System (INIS)

Yamaguchi, Shigeo; Kariya, Michihiko; Kosaki, Masayoshi; Yukawa, Yohei; Nitta, Shugo; Amano, Hiroshi; Akasaki, Isamu

2001-01-01

We study the effect of a combination of N 2 and H 2 carrier gases on the residual strain and crystalline properties of GaN, and we propose its application to the improvement of crystalline quality of GaN/Al 0.17 Ga 0.83 N multiple quantum well (MQW) structures. GaN was grown with H 2 or N 2 carrier gas (H 2 - or N 2 - GaN) on an AlN low-temperature-deposited buffer layer. A (0001) sapphire substrate was used. N 2 - GaN was grown on H 2 - GaN. The total thickness was set to be 1.5 μm, and the ratio of N 2 - GaN thickness to the total thickness, x, ranged from 0 to 1. With increasing x, the tensile stress in GaN increased. Photoluminescence intensity at room temperature was much enhanced. Moreover, the crystalline quality of GaN/Al 0.17 Ga 0.83 N MQW was much higher when the MQW was grown with N 2 on H 2 - GaN than when it was grown with H 2 on H 2 - GaN. These results were due to the achievement of control of strain in GaN using a combination of N 2 - GaN and H 2 - GaN. [copyright] 2001 American Institute of Physics

GaN growth on silane exposed AlN seed layers

Energy Technology Data Exchange (ETDEWEB)

Ruiz-Zepeda, F. [Posgrado en Fisica de Materiales, Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Km. 107 Carret, Tijuana-Ensenada, C.P. 22860, Ensenada, B.C. (Mexico); Contreras, O. [Centro de Ciencias de la Materia Condesada, Universidad Nacional Autonoma de Mexico, Apdo. Postal 356, C.P. 22800, Ensenada, B.C. (Mexico); Dadgar, A.; Krost, A. [Otto-von-Guericke-Universitaet Magdeburg, FNW-IEP, Universitaetsplatz 2, 39106 Magdeburg (Germany)

2008-07-01

The microstructure and surface morphology of GaN films grown on AlN seed layers exposed to silane flow has been studied by TEM and AFM. The epilayers were grown on silicon(111) substrates by MOCVD. The AlN seed layer surface was treated at different SiH{sub 4} exposure times prior to the growth of the GaN film. A reduction in the density of threading dislocations is observed in the GaN films and their surface roughness is minimized for an optimal SiH{sub 4} exposure time between 75-90 sec. At this optimal condition a step-flow growth mode of GaN film is predominant. The improvement of the surface and structure quality of the epilayers is observed to be related to an annihilation process of threading dislocations done by SiN{sub x} masking. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

International Nuclear Information System (INIS)

Zhong Guohua; Zhang Kang; He Fan; Ma Xuhang; Lu Lanlan; Liu Zhuang; Yang Chunlei

2012-01-01

Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce-Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin-orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.

Thermal Annealing induced relaxation of compressive strain in porous GaN structures

KAUST Repository

Ben Slimane, Ahmed

2012-01-01

The effect of annealing on strain relaxation in porous GaN fabricated using electroless chemical etching is presented. The Raman shift of 1 cm-1 in phonon frequency of annealed porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive strain by 0.41 ± 0.04 GPa. The strain relief promises a marked reduction in threading dislocation for subsequent epitaxial growth.

The growth of axially modulated p–n GaN nanowires by plasma-enhanced chemical vapor deposition

International Nuclear Information System (INIS)

Wu, Tung-Hsien; Hong, Franklin Chau-Nan

2013-01-01

Due to the n-type characteristics of intrinsic gallium nitride, p-type gallium nitride (GaN) is more difficult to synthesize than n-type gallium nitride in forming the p–n junctions for optoelectronic applications. For the growth of the p-type gallium nitride, magnesium is used as the dopant. The Mg-doped GaN nanowires (NWs) have been synthesized on (111)-oriented n + -silicon substrates by plasma-enhanced chemical vapor deposition. The scanning electron microscope images showed that the GaN NWs were bent at high Mg doping levels, and the transmission electron microscope characterization indicated that single-crystalline GaN NWs grew along < 0001 > orientation. As shown by energy dispersive spectroscopy, the Mg doping levels in GaN NWs increased with increasing partial pressure of magnesium nitride, which was employed as the dopant precursor for p-GaN NW growth. Photoluminescence measurements suggested the presence of both p- and n‐type GaN NWs. Furthermore, the GaN NWs with axial p–n junctions were aligned between either two-Ni or two-Al electrodes by applying alternating current voltages. The current–voltage characteristics have confirmed the formation of axial p–n junctions in GaN nanowires. - Highlights: ► Grow axially modulated GaN nanowires by plasma-enhanced chemical vapor deposition ► Control the Mg concentration of GaN nanowires by tuning Mg 3 N 2 temperature ► Align the GaN nanowires by applying alternating current voltages between electrodes

Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

International Nuclear Information System (INIS)

Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok; Jeon, In-Jun; Ahn, Hyung Soo; Yi, Sam Nyung; Ha, Dong Han

2015-01-01

Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices

Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

Energy Technology Data Exchange (ETDEWEB)

Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Jeon, In-Jun [Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ahn, Hyung Soo [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Yi, Sam Nyung, E-mail: snyi@kmou.ac.kr [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ha, Dong Han [Division of Convergence Technology, Korea Research Institute of Standards and Science, Daejeon 305-340 (Korea, Republic of)

2015-08-15

Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.

Characterization of plasma etching damage on p-type GaN using Schottky diodes

International Nuclear Information System (INIS)

Kato, M.; Mikamo, K.; Ichimura, M.; Kanechika, M.; Ishiguro, O.; Kachi, T.

2008-01-01

The plasma etching damage in p-type GaN has been characterized. From current-voltage and capacitance-voltage characteristics of Schottky diodes, it was revealed that inductively coupled plasma (ICP) etching causes an increase in series resistance of the Schottky diodes and compensation of acceptors in p-type GaN. We investigated deep levels near the valence band of p-type GaN using current deep level transient spectroscopy (DLTS), and no deep level originating from the ICP etching damage was observed. On the other hand, by capacitance DLTS measurements for n-type GaN, we observed an increase in concentration of a donor-type defect with an activation energy of 0.25 eV after the ICP etching. The origin of this defect would be due to nitrogen vacancies. We also observed this defect by photocapacitance measurements for ICP-etched p-type GaN. For both n- and p-type GaN, we found that the low bias power ICP etching is effective to reduce the concentration of this defect introduced by the high bias power ICP etching

Determination of Optimum Window to External Wall Ratio for Offices in a Hot and Humid Climate

Directory of Open Access Journals (Sweden)

Halil Alibaba

2016-02-01

Full Text Available Heat loss and gain through windows has a very high impact on the thermal comfort of offices. This paper analyzes a standard low energy consumption university office that has a standard envelope. Dynamic thermal simulations with EDSL Tas software, a predicted mean vote (PMV, and a predicted percentage of dissatisfied (PPD with all local discomfort as stated in ASHRAE, ISO 7730: 2005, EN 15251: 2007 were used for thermal sensation, in order to optimize the best window to external wall proportion in a hot and humid climate that exists in the Famagusta case study. A simulated office building is oriented east to west in order to take advantage of the wind direction. In May 45% (PPD < 6%–0.7% open window, 93% (PPD < 10–0.2 open window, and 97% (PPD < 15%–0.1% open window thermal comfort scores are obtained when the window to external wall ratio (WWR is 10%. In October 43% (PPD < 6%–0.7% open window, 86% (PPD < 10–0.2 open window, and 92% (PPD < 15%–0.1% open window thermal comfort scores are obtained when the WWR is 10%. In September 49% (PPD < 10% full open window and 51% (PPD < 15%–0.1% open window thermal comfort scores are obtained when the WWR is 10%.

Transient atomic behavior and surface kinetics of GaN

International Nuclear Information System (INIS)

Moseley, Michael; Billingsley, Daniel; Henderson, Walter; Trybus, Elaissa; Doolittle, W. Alan

2009-01-01

An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.

Transient atomic behavior and surface kinetics of GaN

Science.gov (United States)

Moseley, Michael; Billingsley, Daniel; Henderson, Walter; Trybus, Elaissa; Doolittle, W. Alan

2009-07-01

An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.

GaN MOSHEMT employing HfO2 as a gate dielectric with partially etched barrier

Science.gov (United States)

Han, Kefeng; Zhu, Lin

2017-09-01

In order to suppress the gate leakage current of a GaN high electron mobility transistor (GaN HEMT), a GaN metal-oxide-semiconductor high electron mobility transistor (MOSHEMT) is proposed, in which a metal-oxide-semiconductor gate with high-dielectric-constant HfO2 as an insulating dielectric is employed to replace the traditional GaN HEMT Schottky gate. A 0.5 μm gate length GaN MOSHEMT was fabricated based on the proposed structure, the {{{Al}}}0.28{{{Ga}}}0.72{{N}} barrier layer is partially etched to produce a higher transconductance without deteriorating the transport characteristics of the two-dimensional electron gas in the channel, the gate dielectric is HfO2 deposited by atomic layer deposition. Current-voltage characteristics and radio frequency characteristics are obtained after device preparation, the maximum current density of the device is 900 mA mm-1, the source-drain breakdown voltage is 75 V, gate current is significantly suppressed and the forward gate voltage swing range is about ten times higher than traditional GaN HEMTs, the GaN MOSHEMT also demonstrates radio frequency characteristics comparable to traditional GaN HEMTs with the same gate length.

Surface coatings deposited by CVD and PVD

International Nuclear Information System (INIS)

Gabriel, H.M.

1982-01-01

The demand for wear and corrosion protective coatings is increasing due to economic facts. Deposition processes in gas atmospheres like the CVD and PVD processes attained a tremendous importance especially in the field of the deposition of thin hard refractory and ceramic coatings. CVD and PVD processes are reviewed in detail. Some examples of coating installations are shown and numerous applications are given to demonstrate the present state of the art. (orig.) [de

Evaluation of CVD silicon carbide for synchrotron radiation mirrors

International Nuclear Information System (INIS)

Takacs, P.Z.

1981-07-01

Chemical vapor deposited silicon carbide (CVD SiC) is a recent addition to the list of materials suitable for use in the harsh environment of synchrotron radiation (SR) beam lines. SR mirrors for use at normal incidence must be ultrahigh vacuum compatible, must withstand intense x-ray irradiation without surface damage, must be capable of being polished to an extremely smooth surface finish, and must maintain surface figure under thermal loading. CVD SiC exceeds the performance of conventional optical materials in all these areas. It is, however, a relatively new optical material. Few manufacturers have experience in producing optical quality material, and few opticians have experience in figuring and polishing the material. The CVD material occurs in a variety of forms, sensitively dependent upon reaction chamber production conditions. We are evaluating samples of CVD SiC obtained commercially from various manufacturers, representing a range of deposition conditions, to determine which types of CVD material are most suitable for superpolishing. At the time of this writing, samples are being polished by several commercial vendors and surface finish characteristics are being evaluated by various analytical methods

Real time spectroscopic ellipsometry investigation of homoepitaxial GaN grown by plasma assisted molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Kim, Tong-Ho; Choi, Soojeong; Wu, Pae; Brown, April [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Moto, Akihiro [Innovation Core SEI, Inc., 3235 Kifer Road, Santa Clara, CA 95051 (United States)

2006-06-15

The growth of GaN by plasma assisted molecular beam epitaxy on GaN template substrates (GaN on sapphire) is investigated with in-situ multi-channel spectroscopic ellipsometry. Growth is performed under various Ga/N flux ratios at growth temperatures in the range 710-780 C. The thermal roughening of the GaN template caused by decomposition of the surface is investigated through the temporal variation of the GaN pseudodielectric function over the temperature range of 650 C to 850 C. The structural, morphological, and optical properties are also discussed. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

High temperature refractive indices of GaN

Energy Technology Data Exchange (ETDEWEB)

Liu, C.; Stepanov, S.; Gott, A.; Shields, P.A.; Zhirnov, E.; Wang, W.N. [Department of Physics, University of Bath, Bath, BA2 7AY (United Kingdom); Steimetz, E.; Zettler, J.T. [LayTec, Helmholtzstr. 13-14, 10587 Berlin (Germany)

2006-06-15

Undoped GaN (u-GaN) films were grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE) on sapphire substrates. In situ optical monitoring was applied to the growth process either using a LayTec EpiR-DA TT spectroscopic reflectometer or Filmetrics F30. Refractive indices of u-GaN films at 1060 C were obtained in a spectral range from 370-900 nm. A peak at 412{+-}5 nm in refractive index spectra was observed, which most likely corresponds to the band-gap of hexagonal GaN at a temperature of 1060 C. Refractive indices below this band-gap are fitted well to the first-order Sellmeier formula. As an example of the applications of the refractive indices, the effective film thicknesses of GaN during the resumption from 3 dimensional (3D) to 2 dimensional (2D) growth have been calculated from the spectra recorded by a LayTec system using the optical constants obtained. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Structural characterisation of GaN and GaN:O thin films

International Nuclear Information System (INIS)

Granville, S.; Budde, F.; Koo, A.; Ruck, B.J.; Trodahl, H.J.; Bittar, A.; Metson, J.B.; James, B.J.; Kennedy, V.J.; Markwitz, A.; Prince, K.E.

2005-01-01

In its crystalline form, the wide band-gap semiconductor GaN is of exceptional interest in the development of suitable materials for short wavelength optoelectronic devices. One of the barriers to its potential usefulness however is the large concentration of defects present even in MBE-grown material often due to the lattice mismatch of the GaN with common substrate materials. Calculations have suggested that GaN films grown with an amorphous structure retain many of the useful properties of the crystalline material, including the wide band-gap and a low density of states in the gap, and thus may be a suitable alternative to the single crystal GaN for a variety of applications. We have performed structural and compositional measurements on heavily disordered GaN thin films with and without measureable O and H concentrations grown using ion-assisted deposition. X-ray diffraction and x-ray absorption fine structure measurements show that stoichiometric films are composed of nanocrystallites of ∼3-4 nm in size and that GaN films containing O to 10 at % or greater are amorphous. Rutherford backscattering spectroscopy (RBS) was performed and nuclear reaction analysis (NRA) measurements were made to determine the elemental composition of the films and elastic recoil detection (ERD) detected the hydrogen concentrations. Secondary ion mass spectroscopy (SIMS) measurements were used to depth profile the films. X-ray photoelectron spectroscopy (XPS) measurements probed the bonding environment of the Ga in the films. (author). 2 figs., 1 tab

Impact Analysis of Window-Wall Ratio on Heating and Cooling Energy Consumption of Residential Buildings in Hot Summer and Cold Winter Zone in China

Directory of Open Access Journals (Sweden)

Qiaoxia Yang

2015-01-01

Full Text Available In order to assess the optimal window-wall ratio and the proper glazing type in different air conditioning system operation modes of residential buildings for each orientation in three typical cities in hot summer and cold winter zone: Chongqing, Shanghai, and Wuhan simulation models were built and analyzed using Designer’s Simulation Toolkit (DeST. The study analyzed the variation of annual heating energy demand, annual cooling energy demand, and the annual total energy consumption in different conditions, including different orientations, patterns of utilization of air conditioning system, window-wall ratio, and types of windows. The results show that the total energy consumption increased when the window-wall ratio is also increased. It appears more obvious when the window orientation is east or west. Furthermore, in terms of energy efficiency, low-emissivity (Low-E glass performs better than hollow glass. From this study, it can be concluded that the influence and sensitivity of window-wall ratio on the total energy consumption are related to the operation mode of air conditioning system, the orientation of outside window, and the glazing types of window. The influence of the factors can be regarded as reference mode for the window-wall ratio when designing residential buildings.

Effect of High-Temperature Annealing on Yellow and Blue Luminescence of Undoped GaN

International Nuclear Information System (INIS)

Chai Xu-Zhao; Zhou Dong; Liu Bin; Xie Zi-Li; Han Ping; Xiu Xiang-Qian; Chen Peng; Lu Hai; Zhang Rong; Zheng You-Dou

2015-01-01

The effect of high-temperature annealing on the yellow and blue luminescence of the undoped GaN is investigated by photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS). It is found that the band-edge emission in the GaN apparently increases, and the yellow luminescence (YL) and blue luminescence (BL) bands dramatically decrease after annealing at 700°C. At the annealing temperature higher than 900°C, the YL and BL intensities show an enhancement for the nitrogen annealed GaN. This fact should be attributed to the increment of the Ga and N vacancies in the GaN decomposition. However, the integrated PL intensity of the oxygen annealed GaN decreases at the temperature ranging from 900°C to 1000°C. This results from the capture of many photo-generated holes by high-density surface states. XPS characterization confirms that the high-density surface states mainly originate from the incorporation of oxygen atoms into GaN at the high annealing temperature, and even induces the 0.34eV increment of the upward band bending for the oxygen annealed GaN at 1000°C. (paper)

The feasibility of tunable p-type Mg doping in a GaN monolayer nanosheet

International Nuclear Information System (INIS)

Xia, Congxin; Peng, Yuting; Wei, Shuyi; Jia, Yu

2013-01-01

Based on density functional theory, the electronic structures, formation energy and transition energy level of a p-type Mg-doped GaN nanosheet are investigated. Numerical results show that the transition energy level decreases monotonously with increasing Mg doping concentration in Mg-doped GaN nanosheet systems, which is lower than that of the Mg-doped bulk GaN case. Moreover, the formation energy calculations indicate that Mg-doped GaN nanosheet structures can be realized under N-rich experimental growth conditions

Secondary ion mass spectrometry analysis of In-doped p-type GaN films

International Nuclear Information System (INIS)

Chiou, C.Y.; Wang, C.C.; Ling, Y.C.; Chiang, C.I.

2003-01-01

SIMS was used to investigate the isoelectronic In-doped p-type GaN films. The growth rate of the p-type GaN film decreased with increasing Mg and In doping. The Mg saturation in GaN was 3.55x10 19 atoms/cm 3 . The role of In as surfactant was evaluated by varying In concentrations and it was observed that the surface appeared smooth with increasing In incorporation. The Mg solubility in p-type GaN improved to 0.0025% molar ratio of the GaN with In incorporation. The In concentration results observed in neutron activation analysis (NAA) were found to be higher by a factor of 2.88 than that observed in SIMS and can be attributed to the difference in sensitivity of the two techniques. Good linearity in the results was observed from both techniques

Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

Directory of Open Access Journals (Sweden)

Wen Hua-Chiang

2010-01-01

Full Text Available Abstract In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

Growth and characterization of Fe nanostructures on GaN

International Nuclear Information System (INIS)

Honda, Yuya; Hayakawa, Satoko; Hasegawa, Shigehiko; Asahi, Hajime

2009-01-01

We have investigated the growth of Fe nanostructures on GaN(0 0 0 1) substrates at room temperature using reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and superconducting quantum interference device magnetometer. Initially, a ring RHEED pattern appears, indicating the growth of polycrystalline α-Fe. At around 0.5 nm deposition, the surface displays a transmission pattern from α-Fe films with the epitaxial relationship of Fe(1 1 0)//GaN(0 0 0 1) and Fe[1 -1 1]//GaN[1 1 -2 0] (Kurdjumov-Sachs (KS) orientational relationship). Further deposition to 1 nm results in the appearance of a new spot pattern together with the pattern from domains with the KS orientation relationship. The newly observed pattern shows that Fe layers are formed with the epitaxial relationship of Fe(1 1 0)//GaN(0 0 0 1) and Fe[0 0 1]//GaN[1 1 -2 0] (Nishiyama-Wasserman (NW) orientational relationship). From STM images for Fe layers with the KS and NW orientational relationships, it can be seen that Fe layers with the KS relationship consist of round-shaped Fe nanodots with below 7 nm in average diameter. These nanodots coalesce to form nanodots elongating along the Fe[1 0 0] direction, and they have the KS orientational relationship. Elongated Fe nanodots with the NW relationship show ferromagnetism while round-shaped Fe nanodots with the KS relationship show super-paramagnetic behavior. We will discuss their magnetic properties in connection with the change in crystalline configurations of nanodots.

Cardiovascular disease (CVD and chronic kidney disease (CKD event rates in HIV-positive persons at high predicted CVD and CKD risk: A prospective analysis of the D:A:D observational study.

Directory of Open Access Journals (Sweden)

Mark A Boyd

2017-11-01

Full Text Available The Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D study has developed predictive risk scores for cardiovascular disease (CVD and chronic kidney disease (CKD, defined as confirmed estimated glomerular filtration rate [eGFR] ≤ 60 ml/min/1.73 m2 events in HIV-positive people. We hypothesized that participants in D:A:D at high (>5% predicted risk for both CVD and CKD would be at even greater risk for CVD and CKD events.We included all participants with complete risk factor (covariate data, baseline eGFR > 60 ml/min/1.73 m2, and a confirmed (>3 months apart eGFR 1%-5%, >5% and fitted Poisson models to assess whether CVD and CKD risk group effects were multiplicative. A total of 27,215 participants contributed 202,034 person-years of follow-up: 74% male, median (IQR age 42 (36, 49 years, median (IQR baseline year of follow-up 2005 (2004, 2008. D:A:D risk equations predicted 3,560 (13.1% participants at high CVD risk, 4,996 (18.4% participants at high CKD risk, and 1,585 (5.8% participants at both high CKD and high CVD risk. CVD and CKD event rates by predicted risk group were multiplicative. Participants at high CVD risk had a 5.63-fold (95% CI 4.47, 7.09, p < 0.001 increase in CKD events compared to those at low risk; participants at high CKD risk had a 1.31-fold (95% CI 1.09, 1.56, p = 0.005 increase in CVD events compared to those at low risk. Participants' CVD and CKD risk groups had multiplicative predictive effects, with no evidence of an interaction (p = 0.329 and p = 0.291 for CKD and CVD, respectively. The main study limitation is the difference in the ascertainment of the clinically defined CVD endpoints and the laboratory-defined CKD endpoints.We found that people at high predicted risk for both CVD and CKD have substantially greater risks for both CVD and CKD events compared with those at low predicted risk for both outcomes, and compared to those at high predicted risk for only CVD or CKD events. This suggests that CVD and

Effects of hydrogen on Mn-doped GaN: A first principles calculation

International Nuclear Information System (INIS)

Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.

2013-01-01

First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed

P- and N-type implantation doping of GaN with Ca and O

International Nuclear Information System (INIS)

Zolper, J.C.; Wilson, R.G.; Pearton, S.J.

1996-01-01

III-N photonic devices have made great advances in recent years following the demonstration of doping of GaN p-type with Mg and n-type with Si. However, the deep ionization energy level of Mg in GaN (∼ 160 meV) limits the ionized of acceptors at room temperature to less than 1.0% of the substitutional Mg. With this in mind, the authors used ion implantation to characterize the ionization level of Ca in GaN since Ca had been suggested by Strite to be a shallow acceptor in GaN. Ca-implanted GaN converted from n-to-p type after a 1,100 C activation anneal. Variable temperature Hall measurements give an ionization level at 169 meV. Although this level is equivalent to that of Mg, Ca-implantation may have advantages (shallower projected range and less straggle for a given energy) than Mg for electronic devices. In particular, the authors report the first GaN device using ion implantation doping. This is a GaN junction field effect transistor (JFET) which employed Ca-implantation. A 1.7 microm JFET had a transconductance of 7 mS/mm, a saturation current at 0 V gate bias of 33 mA/mm, a f t of 2.7 GHz, and a f max of 9.4 GHz. O-implantation was also studied and shown to create a shallow donor level (∼ 25 meV) that is similar to Si. SIMS profiles of as-implanted and annealed samples showed no measurable redistribution of either Ca or O in GaN at 1,125 C

Integrated GaN photonic circuits on silicon (100) for second harmonic generation

OpenAIRE

Xiong, Chi; Pernice, Wolfram; Ryu, Kevin K.; Schuck, Carsten; Fong, King Y.; Palacios, Tomas; Tang, Hong X.

2014-01-01

We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The \\{chi}(2) nonlinear susceptibility is measured to be as high as 16 plus minus 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and ...

Experiment and equipment of depositing diamond films with CVD system

International Nuclear Information System (INIS)

Xie Erqing; Song Chang'an

2002-01-01

CVD (chemical vapor deposition) emerged in recent years is a new technique for thin film deposition, which play a key role in development of modern physics. It is important to predominate the principle and technology of CVD for studying modern physics. In this paper, a suit of CVD experimental equipment for teaching in college physics is presented, which has simple design and low cost. The good result was gained in past teaching practices

Catalyst Design Using Nanoporous Iron for the Chemical Vapor Deposition Synthesis of Single-Walled Carbon Nanotubes

Directory of Open Access Journals (Sweden)

Tarek M. Abdel-Fattah

2013-01-01

Full Text Available Single-walled carbon nanotubes (SWNTs have been synthesized via a novel chemical vapor deposition (CVD approach utilizing nanoporous, iron-supported catalysts. Stable aqueous dispersions of the CVD-grown nanotubes using an anionic surfactant were also obtained. The properties of the as-produced SWNTs were characterized through atomic force microscopy and Raman spectroscopy and compared with purified SWNTs produced via the high-pressure CO (HiPCO method as a reference, and the nanotubes were observed with greater lengths than those of similarly processed HiPCO SWNTs.

Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure.

Science.gov (United States)

Yang, Chao; Xi, Xin; Yu, Zhiguo; Cao, Haicheng; Li, Jing; Lin, Shan; Ma, Zhanhong; Zhao, Lixia

2018-02-14

On the basis of the laterally porous GaN, we designed and fabricated a composite porous GaN structure with both well-ordered lateral and vertical holes. Compared to the plane GaN, the composite porous GaN structure with the combination of the vertical holes can help to reduce UV reflectance and increase the saturation photocurrent during water splitting by a factor of ∼4.5. Furthermore, we investigated the underlying mechanism for the enhancement of the water splitting performance using a finite-difference time-domain method. The results show that the well-ordered vertical holes can not only help to open the embedded pore channels to the electrolyte at both sides and reduce the migration distance of the gas bubbles during the water splitting reactions but also help to modulate the light field. Using this composite porous GaN structure, most of the incident light can be modulated and trapped into the nanoholes, and thus the electric fields localized in the lateral pores can increase dramatically as a result of the strong optical coupling. Our findings pave a new way to develop GaN photoelectrodes for highly efficient solar water splitting.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite.

Science.gov (United States)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-27

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

In-situ measurement of the strain relaxation of GaN nanograins during X-ray irradiation

International Nuclear Information System (INIS)

Choe, Hyeokmin; Lee, Sanghwa; Sohn, Yuri; Kim, Chinkyo

2008-01-01

GaN nanograins were grown on a c-plane sapphire substrate and their strain relaxation due to X-ray irradiation was investigated in-situ by utilizing synchrotron xray scattering. The GaN nanograins were constantly exposed to the synchrotron X-ray and θ-2θ scans through the (002) Bragg peak of GaN were repeatedly carried out during the irradiation. The Bragg peak of the compressively strained GaN nanograins gradually shifted toward higher angle, which implies that the GaN nanograins in compressive strain experienced strain relaxation during X-ray irradiation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

Science.gov (United States)

Sharma, Venus; Srivastava, Sunita

2018-04-01

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Forming of High-strength Steels Using a Hot-melt Dry Lubricant

DEFF Research Database (Denmark)

Hörnström, Sven-Erik; Karlsson, Erik; Olsson, Mikael

2008-01-01

during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency to galling in metal forming, including the development of new dry lubricants, new forming tool...... steel grades and improved surface engineering treatments such as the deposition of low friction CVD and PVD coatings. In the present study the performance of a hot-melt dry lubricant in the forming of hot and cold rolled and hot-dip galvanized high strength steel has been evaluated and compared...... with a conventional rust protection oil using four different tests methods, i.e. a strip reduction test, a bending under tension test, a stretch-forming test and a pin-on disc test. In the tests, two different cold work tool steels, a conventional steel grade and a nitrogen alloyed PM steel grade were evaluated...

Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination

Science.gov (United States)

2016-06-01

Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination Distribution Statement A. Approved for public release; distribution is...Final Technical Report BRBAA08-Per5-Y-1-2-0030 Title: “Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination ” Grant...Analysis  .............................................................................................  23   6.   Gamma-ray Discrimination

Dislocation core structures in Si-doped GaN

International Nuclear Information System (INIS)

Rhode, S. L.; Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J.; Horton, M. K.; Pennycook, T. J.; Dusane, R. O.; Moram, M. A.

2015-01-01

Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10 8  and (10 ± 1) × 10 9  cm −2 . All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN

Dislocation core structures in Si-doped GaN

Energy Technology Data Exchange (ETDEWEB)

Rhode, S. L., E-mail: srhode@imperial.ac.uk; Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Horton, M. K. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom); Pennycook, T. J. [SuperSTEM, STFC Daresbury Laboratories, Warrington WA4 4AD (United Kingdom); Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Dusane, R. O. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076 (India); Moram, M. A. [Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)

2015-12-14

Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10{sup 8} and (10 ± 1) × 10{sup 9} cm{sup −2}. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN.

Reduction of single-walled carbon nanotube diameter to sub-nm via feedstock

Energy Technology Data Exchange (ETDEWEB)

Thurakitseree, T.; Zhao, Pei; Chiashi, Shohei; Maruyama, Shigeo [Department of Mechanical Engineering, University of Tokyo (Japan); Kramberger, Christian [Faculty of Physics, University of Vienna (Austria); Einarsson, Erik [Department of Mechanical Engineering, University of Tokyo (Japan); Global Center of Excellence for Mechanical Systems Innovation, University of Tokyo (Japan)

2012-12-15

Vertically aligned single-walled carbon nanotube arrays were synthesized from dip-coated binary Co/Mo catalyst by no-flow chemical vapor deposition (CVD) from either pure ethanol or acetonitrile as carbon feedstock. By changing to acetonitrile the mean diameter was reduced from 2.1 nm to less than 1.0 nm despite using identically prepared catalyst. The demonstrated diameter control on flat substrates is a versatile approach towards the direct synthesis of tailored single-walled carbon nanotubes. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Application of Cat-CVD for ULSI technology

International Nuclear Information System (INIS)

Akasaka, Yoichi

2008-01-01

The ULSI technology has been following Moore's law into the sub-100 nm era, although several challenging technical issues must be resolved. This paper describes possible application of Cat-CVD for ULSI technology beyond the 45 nm node. Especially, Cat-CVD SiN film for a transistor gate sidewall and/or a pre-metallic liner layer, and removal of photo resist (ash) by Cat-induced hydrogen atoms in the interconnect structure with an extreme low-k material are mainly discussed

Real time ellipsometry for monitoring plasma-assisted epitaxial growth of GaN

Energy Technology Data Exchange (ETDEWEB)

Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Losurdo, Maria [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy)]. E-mail: maria.losurdo@ba.imip.cnr.it; Giangregorio, Maria M. [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Capezzuto, Pio [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Brown, April S. [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Kim, Tong-Ho [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Choi, Soojeong [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States)

2006-10-31

GaN is grown on Si-face 4H-SiC(0 0 0 1) substrates using remote plasma-assisted methods including metalorganic chemical vapour deposition (RP-MOCVD) and molecular beam epitaxy (MBE). Real time spectroscopic ellipsometry is used for monitoring all the steps of substrate pre-treatments and the heteroepitaxial growth of GaN on SiC. Our characterization emphasis is on understanding the nucleation mechanism and the GaN growth mode, which depend on the SiC surface preparation.

Electron holography studies of the charge on dislocations in GaN

Energy Technology Data Exchange (ETDEWEB)

Cherns, D.; Jiao, C.G.; Mokhtari, H. [H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Cai, J.; Ponce, F.A. [Department of Physics and Astronomy, Arizona State University, Tempe, AZ85287 (United States)

2002-12-01

The measurement of charge on dislocations in GaN by electron holography is described. Recent results are presented showing that edge dislocations in n-doped GaN are highly negatively charged, whereas those in p-doped GaN are positively charged. It is shown that the results are consistent with a model which assumes Fermi level pinning at dislocation states about 2.5 V below the conduction band edge. The application of electron holography to screw dislocations, and the dependence of the observations on the dislocation core structure, are also discussed. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

Ballistic Josephson junctions based on CVD graphene

Science.gov (United States)

Li, Tianyi; Gallop, John; Hao, Ling; Romans, Edward

2018-04-01

Josephson junctions with graphene as the weak link between superconductors have been intensely studied in recent years, with respect to both fundamental physics and potential applications. However, most of the previous work was based on mechanically exfoliated graphene, which is not compatible with wafer-scale production. To overcome this limitation, we have used graphene grown by chemical vapour deposition (CVD) as the weak link of Josephson junctions. We demonstrate that very short, wide CVD-graphene-based Josephson junctions with Nb electrodes can work without any undesirable hysteresis in their electrical characteristics from 1.5 K down to a base temperature of 320 mK, and their gate-tuneable critical current shows an ideal Fraunhofer-like interference pattern in a perpendicular magnetic field. Furthermore, for our shortest junctions (50 nm in length), we find that the normal state resistance oscillates with the gate voltage, consistent with the junctions being in the ballistic regime, a feature not previously observed in CVD-graphene-based Josephson junctions.

Investigation on the electron flux to the wall in the VENUS ion source

Energy Technology Data Exchange (ETDEWEB)

Thuillier, T., E-mail: thuillier@lpsc.in2p3.fr; Angot, J. [LPSC, Université Grenoble-Alpes, CNRS/IN2P3, 53 rue des Martyrs, 38026 Grenoble Cedex (France); Benitez, J. Y.; Hodgkinson, A.; Lyneis, C. M.; Todd, D. S.; Xie, D. Z. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2016-02-15

The long-term operation of high charge state electron cyclotron resonance ion sources fed with high microwave power has caused damage to the plasma chamber wall in several laboratories. Porosity, or a small hole, can be progressively created in the chamber wall which can destroy the plasma chamber over a few year time scale. A burnout of the VENUS plasma chamber is investigated in which the hole formation in relation to the local hot electron power density is studied. First, the results of a simple model assuming that hot electrons are fully magnetized and strictly following magnetic field lines are presented. The model qualitatively reproduces the experimental traces left by the plasma on the wall. However, it is too crude to reproduce the localized electron power density for creating a hole in the chamber wall. Second, the results of a Monte Carlo simulation, following a population of scattering hot electrons, indicate a localized high power deposited to the chamber wall consistent with the hole formation process. Finally, a hypervapotron cooling scheme is proposed to mitigate the hole formation in electron cyclotron resonance plasma chamber wall.

GaN epilayers on nanopatterned GaN/Si(1 1 1) templates: Structural and optical characterization

International Nuclear Information System (INIS)

Wang, L.S.; Tripathy, S.; Wang, B.Z.; Chua, S.J.

2006-01-01

Template-based nanoscale epitaxy has been explored to realize high-quality GaN on Si(1 1 1) substrates. We have employed polystyrene-based nanosphere lithography to form the nano-hole array patterns on GaN/Si(1 1 1) template and then, subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition (MOCVD). During the initial growth stage of GaN on such nanopatterned substrates, we have observed formation of nanoislands with hexagonal pyramid shape due to selective area epitaxy. With further epitaxial regrowth, these nanoislands coalesce and form continuous GaN film. The overgrown GaN on patterned and non-patterned regions is characterized by high-resolution X-ray diffraction (HRXRD) and high-spatial resolution optical spectroscopic methods. Micro-photoluminescence (PL), micro-Raman scattering and scanning electron microscopy (SEM) have been used to assess the microstructural and optical properties of GaN. Combined PL and Raman data analyses show improved optical quality when compared to GaN simultaneously grown on non-patterned bulk Si(1 1 1). Such thicker GaN templates would be useful to achieve III-nitride-based opto- and electronic devices integrated on Si substrates

The study of electronic structures and optical properties of Al-doped GaN

International Nuclear Information System (INIS)

Li Enling; Hou Liping; Liu Mancang; Xi Meng; Wang Xiqiang; Dai Yuanbin; Li Lisha

2011-01-01

The electronic structures and optical properties of undoped and Al-doped GaN (Al x Ga 1-x N, x=0.0625, 0.125, 0.25) have been studied based on generalized gradient approximation (GGA) method of density functional theory (DFT). The differences of the electronic structures and optical properties of undoped and Al-doped GaN have been discussed in detail. The result shows: according to total density of state of undoped and Al-doped GaN, the conduction band becomes width and moves to high energy level with gradual increase concentration of Al impurity. Impurity energy band isn't found in energy band structures of Al x Ga 1-x N, the same as energy band structures of undoped GaN, but the band gaps gradually become wide with increase of Al impurity. Absorption spectra of undoped and Al-doped GaN of main absorption peak moves to high energy level with increase of Al impurity.

Mg doping of GaN by molecular beam epitaxy

International Nuclear Information System (INIS)

Lieten, R R; Buchowicz, G; Dubon, O; Motsnyi, V; Zhang, L; Cheng, K; Leys, M; Degroote, S; Borghs, G

2011-01-01

We present a systematic study on the influence of growth conditions on the incorporation and activation of Mg in GaN layers grown by plasma-assisted molecular beam epitaxy. We show that high quality p-type GaN layers can be obtained on GaN-on-silicon templates. The Mg incorporation and the electrical properties have been investigated as a function of growth temperature, Ga : N flux ratio and Mg : Ga flux ratio. It was found that the incorporation of Mg and the electrical properties are highly sensitive to the Ga : N flux ratio. The highest hole mobility and lowest resistivity were achieved for slightly Ga-rich conditions. In addition to an optimal Ga : N ratio, an optimum Mg : Ga flux ratio was also observed at around 1%. We observed a clear Mg flux window for p-type doping of GaN : 0.31% 17 cm -3 and a mobility of 15 cm 2 V -1 s -1 . Temperature-dependent Hall effect measurements indicate an acceptor depth in these samples of 100 meV for a hole concentration of 5.5 x 10 17 cm -3 . The corresponding Mg concentration is 5 x 10 19 cm -3 , indicating approximately 1% activation at room temperature. In addition to continuous growth of Mg-doped GaN layers we also investigated different modulated growth procedures. We show that a modulated growth procedure has only limited influence on Mg doping at a growth temperature of 800 deg. or higher. This result is thus in contrast to previously reported GaN : Mg doping at much lower growth temperatures of 500 deg. C.

Growth of GaN on Sapphire via Low-Temperature Deposited Buffer Layer and Realization of p-Type GaN by Mg Doping Followed by Low-Energy Electron Beam Irradiation

Science.gov (United States)

Amano, Hiroshi

2015-12-01

This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid- to late 80s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed.

Hot-cell shielding system for high power transmission in DUPIC fuel fabrication

International Nuclear Information System (INIS)

Kim, K.; Lee, J.; Park, J.; Yang, M.; Park, H.

2000-01-01

This paper presents a newly designed hot-cell shielding system for use in the development of DUPIC (Direct Use of spent PWR fuel In CANDU reactors) fuel at KAERI (Korea Atomic Energy Research Institute). This hot-cell shielding system that was designed to transmit high power to sintering furnace in-cell from the out-of-cell through a thick cell wall has three subsystems - a steel shield plug with embedded spiral cooling line, stepped copper bus bars, and a shielding lead block. The dose-equivalent rates of the hot-cell shielding system and of the apertures between this system and the hot-cell wall were calculated. Calculated results were compared with the allowable dose limit of the existing hot-cell. Experiments for examining the temperature changes of the shielding system developed during normal furnace operation were also carried out. Finally, gamma-ray radiation survey experiments were conducted by Co-60 source. It is demonstrated that, from both calculated and experimental results, the newly designed hot-cell shielding system meets all the shielding requirements of the existing hot-cell facility, enabling high power transmission to the in-cell sintering furnace. (author)

Studies on electronic structure of GaN(0001) surface

CERN Document Server

Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

2002-01-01

An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

Effect of H, O intentionally doping on photoelectric properties in MOVPE-growth GaN layers

KAUST Repository

Ohkawa, Kazuhiro

2017-10-24

GaN crystal growth requires higher purity of materials. Some contaminants in NH3 gas could be the causal factor of defects in GaN crystals. These atoms act as donor or acceptor. In order to clearly demonstrate the effect of gaseous impurities such as H2O on the properties of undoped-GaN layer, high purity NH3 (N70) was used as NH3 source. The concentration of H2O in NH3 was varied at 32, 49, 75, 142, 266, 489, and 899 ppb, respectively. Under the same recipe, we deposited undoped-GaN epitaxial layer with purifier, and H2O-doped GaN series layers. As similar to the results of CO and CO2-doped GaN series, the increase tendency of carrier density changing with increasing H2O concentration. The FWHMs of XRC around (0002) remain stable, witnessing that the crystal quality of GaN layer remain good. LT (15K) PL of undoped-GaN and H2O-doped GaN were measured, the D0X emission peak intensity of all H2O-doped GaN are decreased drastically compared with undoped-GaN. H2O impurity was doped into GaN layer, which not only effects electrical properties and but also effects the radiative emission and furthermore effects PL intensity, its mechanism is discussed.

CVD and obesity in transitional Syria: a perspective from the Middle East.

Science.gov (United States)

Barakat, Hani; Barakat, Hanniya; Baaj, Mohamad K

2012-01-01

Syria is caught in the middle of a disruptive nutritional transition. Its healthcare system is distracted by challenges and successes in other areas while neglecting to address the onslaught of Syria's cardiovascular disease (CVD) epidemic. Despite the official viewpoint touting improvement in health indicators, current trends jeopardize population health, and several surveys in the Syrian population signal the epidemic spreading far and wide. The goal is to counteract the indifference towards obesity as a threat to Syrian's health, as the country is slowly becoming a leader in CVD mortality globally. PubMed, World Health Organization, and official government websites were searched for primary surveys in Syria related to CVD morbidity, mortality, and risk factors. Inclusion criteria ensured that results maximized relevance while producing comparable studies. Statistical analysis was applied to detect the most common risk factor and significant differences in risk factor prevalence and CVD rates. Obesity remained the prevailing CVD risk factor except in older Syrian men, where smoking and hypertension were more common. CVD mortality was more common in males due to coronary disease, while stroke dominated female mortality. The young workforce is especially impacted, with 50% of CVD mortality occurring before age 65 years and an 81% prevalence of obesity in women over 45 years. Syria can overcome its slow response to the CVD epidemic and curb further deterioration by reducing obesity and, thus, inheritance and clustering of risk factors. This can be achieved via multilayered awareness and intensive parental and familial involvement. Extinguishing the CVD epidemic is readily achievable as demonstrated in other countries.

Dysprosium-Catalyzed Growth of Single-Walled Carbon Nanotube Arrays on Substrates

Directory of Open Access Journals (Sweden)

Qian Yong

2009-01-01

Full Text Available Abstract In this letter, we report that dysprosium is an effective catalyst for single-walled carbon nanotubes (SWNTs growth via a chemical vapor deposition (CVD process for the first time. Horizontally superlong well-oriented SWNT arrays on SiO2/Si wafer can be fabricated by EtOH-CVD under suitable conditions. The structure and properties are characterized by scanning electron microscopy, transition electron microscopy, Raman spectroscopy and atomic force microscopy. The results show that the SWNTs from dysprosium have better structural uniformity and better conductivity with fewer defects. This rare earth metal provides not only an alternative catalyst for SWNTs growth, but also a possible method to generate high percentage of superlong semiconducting SWNT arrays for various applications of nanoelectronic device.

Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

Science.gov (United States)

Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

1996-01-01

The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

Study on the influence of annealing effects in GaN VPE

International Nuclear Information System (INIS)

Furtado, M.

1983-06-01

The effects of annealing that occur during VPE growth of GaN were investigated. GaN powder (and epilayers) samples were annealed in Ar, N 2 , H 2 , NH 3 , HC1 + N 2 and HC1 + H 2 (N 2 , H 2 and HC1 + N 2 ), respectively; under a range of experimental conditions of interest for preparing electroluminescent devices. Good surface appearence Zn doped epilayers were also used under 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 HC1. The epilayers' behaviour under thermal decomposition and HC1 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 [pt

Step-flow growth mode instability of N-polar GaN under N-excess

International Nuclear Information System (INIS)

Chèze, C.; Sawicka, M.; Siekacz, M.; Łucznik, B.; Boćkowski, M.; Skierbiszewski, C.; Turski, H.; Cywiński, G.; Smalc-Koziorowska, J.; Weyher, J. L.; Kryśko, M.

2013-01-01

GaN layers were grown on N-polar GaN substrates by plasma-assisted molecular beam epitaxy under different III/V ratios. Ga-rich conditions assure step-flow growth with atomically flat surface covered by doubly-bunched steps, as for Ga-polar GaN. Growth under N-excess however leads to an unstable step-flow morphology. Particularly, for substrates slightly miscut towards , interlacing fingers are covered by atomic steps pinned on both sides by small hexagonal pits. In contrast, a three-dimensional island morphology is observed on the Ga-polar equivalent sample. We attribute this result to lower diffusion barriers on N-polar compared to Ga-polar GaN under N-rich conditions

Structural and optical properties of Si-doped GaN

OpenAIRE

Cremades Rodríguez, Ana Isabel; Gorgens, L.; Ambacher, O.; Stutzmann, M.; Scholz, F.

2000-01-01

Structural and optical properties of Si-doped GaN thin films grown by metal-organic chemical vapor deposition have been studied by means of high resolution x-ray diffraction (XRD), atomic force microscopy, photoluminescence, photothermal deflection spectroscopy, and optical transmission measurements. The incorporation of silicon in the GaN films leads to pronounced tensile stress. The energy position of the neutral donor bound excitonic emission correlates with the measured stress. The stress...

Investigation of defects in CVD diamond: Influence for radiotherapy applications

International Nuclear Information System (INIS)

Guerrero, M.J.; Tromson, D.; Bergonzo, P.; Barrett, R.

2005-01-01

In this study we present the potentialities of CVD diamond as an ionisation chamber for radiotherapy applications. Trapping levels present in CVD diamond are characterised using Thermally Stimulated Current (TSC) method with X-ray sources. The influence of the corresponding defects on the detector response is investigated and compared to those observed in natural diamond. Also, their spatial distribution across a large area polycrystalline diamond ionisation chamber is discussed. Results show the relative influence of two different populations of trapping levels in CVD diamond whose effect is crucial for radiotherapy applications. To partially overcome the defect detrimental effects, we propose to use CVD diamond ionisation chambers at moderate temperatures from 70 to 100 deg. C that could be provided by self heating of the device, for a dramatically improved stability and reproducibility

The formation of tritium permeation barriers by CVD

International Nuclear Information System (INIS)

Forcey, K.S.; Perujo, A.; Reiter, F.; Lolli-Ceroni, P.L.

1993-01-01

The effectiveness as permeation barriers of the following CVD coatings have been investigated: TiC (1 to 2 μm in thickness); a bi-layer of TiN on TiC (3 μm total thickness) and CVD Al 2 O 3 on a TiN/TiC bi-layer. The substrate materials were TZM (a Mo alloy) and 316L stainless steel in the form of discs of diameter 48 mm and thickness 0.1 or 1 mm. Permeation measurements were performed in the temperature range 515-742 K using deuterium at pressures in the range 1-50 kPa. CVD layers were shown to form reasonably effective permeation barriers. At a temperature of 673 K TiC is around 6000 times less permeable to deuterium than 316L stainless steel. (orig.)

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

Science.gov (United States)

Ueno, Kohei; Fudetani, Taiga; Arakawa, Yasuaki; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

2017-12-01

We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD) technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm-3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V-1 s-1 at a carrier concentration of 3.9 × 1020 cm-3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

Directory of Open Access Journals (Sweden)

Kohei Ueno

2017-12-01

Full Text Available We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm−3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V−1 s−1 at a carrier concentration of 3.9 × 1020 cm−3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

A density functional theory study of the TMG adsorption on the GaN surface

Energy Technology Data Exchange (ETDEWEB)

Ptasinska, Maria; Soltys, Jakub; Piechota, Jacek [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Krukowski, Stanislaw [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokolowska 29/37, 01-142 Warsaw (Poland)

2011-07-01

TMG (trimetylogallium) and NH{sub 3} (ammonia) are widely used reactants in the metal organic chemical vapor deposition (MOCVD) technique used in the growth of the GaN thin films. We have recently examined theoretically, with the help of the density functional theory (DFT), TMG adsorption on the GaN(0001) surface in order to study formation of bonds between Ga and N. Dangling bonds on the GaN(0001) surface were saturated with the hydrogen atoms. The slab polarization, which is due to the dangling bonds present on the GaN(0001) surface, and energy of the system in the vicinity of TMG was computed for different distances between the surface atoms and TMG. We also studied TMG diffusion on the GaN surface. As a result, the energy path for diffusion from Top N to Hollow was obtained.

Conduction, reverse conduction and switching characteristics of GaN E-HEMT

DEFF Research Database (Denmark)

Sørensen, Charlie; Lindblad Fogsgaard, Martin; Christiansen, Michael Noe

2015-01-01

In this paper switching and conduction characterization of the GS66508P-E03 650V enhancement mode gallium nitride (GaN) transistor is described. GaN transistors are leading edge technology and as so, their characteristics are less than well documented. The switching characteristics are found using...

Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

Science.gov (United States)

Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

2016-09-01

For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

Controlled surface diffusion in plasma-enhanced chemical vapor deposition of GaN nanowires

International Nuclear Information System (INIS)

Hou, W C; Hong, Franklin Chau-Nan

2009-01-01

This study investigates the growth of GaN nanowires by controlling the surface diffusion of Ga species on sapphire in a plasma-enhanced chemical vapor deposition (CVD) system. Under nitrogen-rich growth conditions, Ga has a tendency to adsorb on the substrate surface diffusing to nanowires to contribute to their growth. The significance of surface diffusion on the growth of nanowires is dependent on the environment of the nanowire on the substrate surface as well as the gas phase species and compositions. Under nitrogen-rich growth conditions, the growth rate is strongly dependent on the surface diffusion of gallium, but the addition of 5% hydrogen in nitrogen plasma instantly diminishes the surface diffusion effect. Gallium desorbs easily from the surface by reaction with hydrogen. On the other hand, under gallium-rich growth conditions, nanowire growth is shown to be dominated by the gas phase deposition, with negligible contribution from surface diffusion. This is the first study reporting the inhibition of surface diffusion effects by hydrogen addition, which can be useful in tailoring the growth and characteristics of nanowires. Without any evidence of direct deposition on the nanowire surface, gallium and nitrogen are shown to dissolve into the catalyst for growing the nanowires at 900 deg. C.

Materials and fabrication processes for operation in hot hydrogen

International Nuclear Information System (INIS)

Tuffias, R.H.; Duffy, A.J.; Arrieta, V.M.; Abrams, W.M.; Benander, R.E.

1997-01-01

Operation in hot (2500 endash 3000 K) hydrogen severely limits the choice of structural materials. Rhenium is nonreactive with and has low permeability to hydrogen, and has sufficient strength up to 2800 K. Carbon, in the form of graphite or carbon composites, has excellent high temperature strength but reacts with hydrogen to form methane at a rapid rate above 2000 K. The carbides of zirconium, niobium, hafnium, and tantalum are nonreactive with and have low permeability to hydrogen, but they can be reliably fabricated only in the form of coatings. In order to demonstrate the Integrated Solar Upper Stage (ISUS) solar-thermal propulsion concept, rhenium and rhenium-coated graphite were chosen as the structural materials for the receiver-absorber-converter (RAC) component of the ISUS system. Several methods were investigated for fabricating the rhenium parts and coatings, with chemical vapor deposition (CVD) and Ultramet chosen as the most likely process and company for success. The CVD or rhenium and other refractory materials were thus applied to the ISUS program for fabrication of the RAC subsystem. copyright 1997 American Institute of Physics

Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN: Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN

Energy Technology Data Exchange (ETDEWEB)

Hossain, T. [Kansas State Univ., Manhattan, KS (United States); Wei, D. [Kansas State Univ., Manhattan, KS (United States); Nepal, N. [Naval Research Lab. (NRL), Washington, DC (United States); Garces, N. Y. [Naval Research Lab. (NRL), Washington, DC (United States); Hite, J. K. [Naval Research Lab. (NRL), Washington, DC (United States); Meyer, H. M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Eddy, C. R. [Naval Research Lab. (NRL), Washington, DC (United States); Baker, Troy [Nitride Solutions, Wichita, KS (United States); Mayo, Ashley [Nitride Solutions, Wichita, KS (United States); Schmitt, Jason [Nitride Solutions, Wichita, KS (United States); Edgar, J. H. [Kansas State Univ., Manhattan, KS (United States)

2014-02-24

We report the benefits of dry oxidation of n -GaN for the fabrication of metal-oxide-semiconductor structures. GaN thin films grown on sapphire by MOCVD were thermally oxidized for 30, 45 and 60 minutes in a pure oxygen atmosphere at 850 °C to produce thin, smooth GaO_x layers. Moreover, the GaN sample oxidized for 30 minutes had the best properties. Its surface roughness (0.595 nm) as measured by atomic force microscopy (AFM) was the lowest. Capacitance-voltage measurements showed it had the best saturation in accumulation region and the sharpest transition from accumulation to depletion regions. Under gate voltage sweep, capacitance-voltage hysteresis was completely absent. The interface trap density was minimum (D_it = 2.75×10¹⁰ cm^–2eV^–1) for sample oxidized for 30 mins. These results demonstrate a high quality GaO_x layer is beneficial for GaN MOSFETs.

Hot air impingement on a flat plate using Large Eddy Simulation (LES) technique

Science.gov (United States)

Plengsa-ard, C.; Kaewbumrung, M.

2018-01-01

Impinging hot gas jets to a flat plate generate very high heat transfer coefficients in the impingement zone. The magnitude of heat transfer prediction near the stagnation point is important and accurate heat flux distribution are needed. This research studies on heat transfer and flow field resulting from a single hot air impinging wall. The simulation is carried out using computational fluid dynamics (CFD) commercial code FLUENT. Large Eddy Simulation (LES) approach with a subgrid-scale Smagorinsky-Lilly model is present. The classical Werner-Wengle wall model is used to compute the predicted results of velocity and temperature near walls. The Smagorinsky constant in the turbulence model is set to 0.1 and is kept constant throughout the investigation. The hot gas jet impingement on the flat plate with a constant surface temperature is chosen to validate the predicted heat flux results with experimental data. The jet Reynolds number is equal to 20,000 and a fixed jet-to-plate spacing of H/D = 2.0. Nusselt number on the impingement surface is calculated. As predicted by the wall model, the instantaneous computed Nusselt number agree fairly well with experimental data. The largest values of calculated Nusselt number are near the stagnation point and decrease monotonically in the wall jet region. Also, the contour plots of instantaneous values of wall heat flux on a flat plate are captured by LES simulation.

Barrier characteristics of Pt/Ru Schottky contacts on n-type GaN ...

Indian Academy of Sciences (India)

Pt/Ru Schottky rectifiers; n-type GaN; temperature–dependent electrical properties; inhomogeneous barrier heights .... a 2 μm thick Si-doped GaN films which were grown by .... ted values of ap using (9) for two Gaussian distributions of bar-.

Evidence for moving of threading dislocations during the VPE growth in GaN thin layers

Energy Technology Data Exchange (ETDEWEB)

Kuwano, Noriyuki [Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Miyake, Hideto; Hiramatsu, Kazumasa [Department of Electrical and Electronic Engineering, Mie University, Tsu, Mie 514-8507 (Japan); Amano, Hiroshi [Graduate School of Engineering, Akasaki Research Center, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603 (Japan); Akasaki, Isamu [Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya 468-8502 (Japan)

2011-05-15

Cross-sectional transmission electron microscope (TEM) observation was performed in detail to analyze the morphology of threading dislocations (TDs) in GaN thin layers with various thicknesses. The GaN layers were overgrown on an Al{sub 0.28}Ga{sub 0.72}N layer by the metal-organic vapor-phase epitaxy (MOVPE) method. In a GaN layer about 50 nm in thickness, TDs running up in the AlGaN layer pass into the GaN layer and most of them reach the top surface without bending. In thicker GaN layers, on the other hand, many of TDs form a hairpin-configuration on or above the interface of GaN and AlGaN to be annihilated. This difference in morphology of TDs indicates that the TDs have moved down inside the GaN layer. Since the formation of hairpins is attributed to a stress-relief, there should be an extra half-plane between the paired TDs. Therefore, the movement of TDs should be of ''climb motion''. Another example of possible TD movement inside a GaN layer is also described. It is emphasized that the possibility of TD-movements inside the thin film crystal during the growth should be taken into account in analysis of thin-layer growth through the behavior of TDs (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

380 keV proton irradiation effects on photoluminescence of Eu-doped GaN

International Nuclear Information System (INIS)

Okada, Hiroshi; Nakanishi, Yasuo; Wakahara, Akihiro; Yoshida, Akira; Ohshima, Takeshi

2008-01-01

The effect of 380 keV proton irradiation on the photoluminescence (PL) properties has been investigated for undoped and Eu-doped GaN. As the proton irradiation exceeds 1x10 13 cm -2 , a drastic decrease of PL intensity of the near band-edge emission of undoped GaN was observed. On the other hand, for Eu-doped GaN, the PL emission corresponding to the 5 D 0 → 7 F 2 transition in Eu 3+ kept the initial PL intensity after the proton irradiation up to 1x10 14 cm -2 . Present results, together with our previous report on electron irradiation results, suggest that Eu-doped GaN is a strong candidate for light emitting devices in high irradiation environment

Optical and Structural Characterizations of GaN Nano structures

International Nuclear Information System (INIS)

Shekari, L.; Abu Hassan, H.; Thahab, S.M.

2011-01-01

We have grown wurtzite GaN nano wires (NWs) on polished silicon (Si) either with or without Au as catalyst, using commercial GaN powder by thermal evaporation in an atmosphere of argon (Ar) gas. Structural and optical characterizations were performed using high resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), photoluminescence (PL) and energy-dispersive X-ray spectroscopy (EDX) spectroscopy. Results indicate that the nano wires are of single-crystal hexagonal GaN and the nano wires on Si with Au catalyst are more oriented than those without Au catalyst; and using catalyst make the NWs grow much faster and quite well-ordered. The compositional quality of the grown nano wires on the substrates are mostly same, however the nano wires on the Au coated silicon are of low density, while the nano wires on the Si are of high density. (author)

Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

International Nuclear Information System (INIS)

Zhao, Qian; Xiong, Zhihua; Luo, Lan; Sun, Zhenhui; Qin, Zhenzhen; Chen, Lanli; Wu, Ning

2017-01-01

Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

Energy Technology Data Exchange (ETDEWEB)

Zhao, Qian [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Xiong, Zhihua, E-mail: xiong_zhihua@126.com [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Luo, Lan [School of Materials Science and Engineering, Nanchang University, Nanchang 330031 (China); Sun, Zhenhui [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Qin, Zhenzhen [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Chen, Lanli [Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Wu, Ning [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China)

2017-02-28

Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

Formation of definite GaN p-n junction by Mg-ion implantation to n--GaN epitaxial layers grown on a high-quality free-standing GaN substrate

Science.gov (United States)

Oikawa, Takuya; Saijo, Yusuke; Kato, Shigeki; Mishima, Tomoyoshi; Nakamura, Tohru

2015-12-01

P-type conversion of n--GaN by Mg-ion implantation was successfully performed using high quality GaN epitaxial layers grown on free-standing low-dislocation-density GaN substrates. These samples showed low-temperature PL spectra quite similar to those observed from Mg-doped MOVPE-grown p-type GaN, consisting of Mg related donor-acceptor pair (DAP) and acceptor bound exciton (ABE) emission. P-n diodes fabricated by the Mg-ion implantation showed clear rectifying I-V characteristics and UV and blue light emissions were observed at forward biased conditions for the first time.

UMA/GAN network architecture analysis

Science.gov (United States)

Yang, Liang; Li, Wensheng; Deng, Chunjian; Lv, Yi

2009-07-01

This paper is to critically analyze the architecture of UMA which is one of Fix Mobile Convergence (FMC) solutions, and also included by the third generation partnership project(3GPP). In UMA/GAN network architecture, UMA Network Controller (UNC) is the key equipment which connects with cellular core network and mobile station (MS). UMA network could be easily integrated into the existing cellular networks without influencing mobile core network, and could provides high-quality mobile services with preferentially priced indoor voice and data usage. This helps to improve subscriber's experience. On the other hand, UMA/GAN architecture helps to integrate other radio technique into cellular network which includes WiFi, Bluetooth, and WiMax and so on. This offers the traditional mobile operators an opportunity to integrate WiMax technique into cellular network. In the end of this article, we also give an analysis of potential influence on the cellular core networks ,which is pulled by UMA network.

Multilayered and composite PVD-CVD coatings in cemented carbides manufacture

International Nuclear Information System (INIS)

Glushkov, V.N.; Anikeev, A.I.; Anikin, V.N.; Vereshchaka, A.S.

2001-01-01

Carbide cutting tools with wear-resistant coatings deposited by CVD process are widely employed in mechanical engineering to ensure a substantially longer service life of tool systems. However, the relatively high temperature and long time of the process make the substrate decarburise and, as a result, the bend strength and performance characteristics of a tool decrease. The present study suggests the problem of deteriorated strength of CVD-coated carbide tools be solved by the development of a technology that combines arc-PVD and CVD processes to deposit multilayered coatings of titanium and aluminium compounds. (author)

Validation of a model to investigate the effects of modifying cardiovascular disease (CVD) risk factors on the burden of CVD: the rotterdam ischemic heart disease and stroke computer simulation (RISC) model.

Science.gov (United States)

van Kempen, Bob J H; Ferket, Bart S; Hofman, Albert; Steyerberg, Ewout W; Colkesen, Ersen B; Boekholdt, S Matthijs; Wareham, Nicholas J; Khaw, Kay-Tee; Hunink, M G Myriam

2012-12-06

We developed a Monte Carlo Markov model designed to investigate the effects of modifying cardiovascular disease (CVD) risk factors on the burden of CVD. Internal, predictive, and external validity of the model have not yet been established. The Rotterdam Ischemic Heart Disease and Stroke Computer Simulation (RISC) model was developed using data covering 5 years of follow-up from the Rotterdam Study. To prove 1) internal and 2) predictive validity, the incidences of coronary heart disease (CHD), stroke, CVD death, and non-CVD death simulated by the model over a 13-year period were compared with those recorded for 3,478 participants in the Rotterdam Study with at least 13 years of follow-up. 3) External validity was verified using 10 years of follow-up data from the European Prospective Investigation of Cancer (EPIC)-Norfolk study of 25,492 participants, for whom CVD and non-CVD mortality was compared. At year 5, the observed incidences (with simulated incidences in brackets) of CHD, stroke, and CVD and non-CVD mortality for the 3,478 Rotterdam Study participants were 5.30% (4.68%), 3.60% (3.23%), 4.70% (4.80%), and 7.50% (7.96%), respectively. At year 13, these percentages were 10.60% (10.91%), 9.90% (9.13%), 14.20% (15.12%), and 24.30% (23.42%). After recalibrating the model for the EPIC-Norfolk population, the 10-year observed (simulated) incidences of CVD and non-CVD mortality were 3.70% (4.95%) and 6.50% (6.29%). All observed incidences fell well within the 95% credibility intervals of the simulated incidences. We have confirmed the internal, predictive, and external validity of the RISC model. These findings provide a basis for analyzing the effects of modifying cardiovascular disease risk factors on the burden of CVD with the RISC model.

Validation of a model to investigate the effects of modifying cardiovascular disease (CVD risk factors on the burden of CVD: the rotterdam ischemic heart disease and stroke computer simulation (RISC model

Directory of Open Access Journals (Sweden)

van Kempen Bob JH

2012-12-01

Full Text Available Abstract Background We developed a Monte Carlo Markov model designed to investigate the effects of modifying cardiovascular disease (CVD risk factors on the burden of CVD. Internal, predictive, and external validity of the model have not yet been established. Methods The Rotterdam Ischemic Heart Disease and Stroke Computer Simulation (RISC model was developed using data covering 5 years of follow-up from the Rotterdam Study. To prove 1 internal and 2 predictive validity, the incidences of coronary heart disease (CHD, stroke, CVD death, and non-CVD death simulated by the model over a 13-year period were compared with those recorded for 3,478 participants in the Rotterdam Study with at least 13 years of follow-up. 3 External validity was verified using 10 years of follow-up data from the European Prospective Investigation of Cancer (EPIC-Norfolk study of 25,492 participants, for whom CVD and non-CVD mortality was compared. Results At year 5, the observed incidences (with simulated incidences in brackets of CHD, stroke, and CVD and non-CVD mortality for the 3,478 Rotterdam Study participants were 5.30% (4.68%, 3.60% (3.23%, 4.70% (4.80%, and 7.50% (7.96%, respectively. At year 13, these percentages were 10.60% (10.91%, 9.90% (9.13%, 14.20% (15.12%, and 24.30% (23.42%. After recalibrating the model for the EPIC-Norfolk population, the 10-year observed (simulated incidences of CVD and non-CVD mortality were 3.70% (4.95% and 6.50% (6.29%. All observed incidences fell well within the 95% credibility intervals of the simulated incidences. Conclusions We have confirmed the internal, predictive, and external validity of the RISC model. These findings provide a basis for analyzing the effects of modifying cardiovascular disease risk factors on the burden of CVD with the RISC model.

Ultra-Low Inductance Design for a GaN HEMT Based 3L-ANPC Inverter

DEFF Research Database (Denmark)

Gurpinar, Emre; Castellazzi, Alberto; Iannuzzo, Francesco

2016-01-01

contributors to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a four layer PCB with the aim to maximise the switching performance of GaN HEMTs is explained. Gate driver design for GaN HEMT devices is presented. Common-mode behaviours......In this paper, an ultra-low inductance power cell design for a 3L-ANPC based on 650 V GaN HEMT devices is presented. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which are the main...

Strain-free GaN thick films grown on single crystalline ZnO buffer layer with in situ lift-off technique

International Nuclear Information System (INIS)

Lee, S. W.; Minegishi, T.; Lee, W. H.; Goto, H.; Lee, H. J.; Lee, S. H.; Lee, Hyo-Jong; Ha, J. S.; Goto, T.; Hanada, T.; Cho, M. W.; Yao, T.

2007-01-01

Strain-free freestanding GaN layers were prepared by in situ lift-off process using a ZnO buffer as a sacrificing layer. Thin Zn-polar ZnO layers were deposited on c-plane sapphire substrates, which was followed by the growth of Ga-polar GaN layers both by molecular beam epitaxy (MBE). The MBE-grown GaN layer acted as a protecting layer against decomposition of the ZnO layer and as a seeding layer for GaN growth. The ZnO layer was completely in situ etched off during growth of thick GaN layers at low temperature by hydride vapor phase epitaxy. Hence freestanding GaN layers were obtained for the consecutive growth of high-temperature GaN thick layers. The lattice constants of freestanding GaN agree with those of strain-free GaN bulk. Extensive microphotoluminescence study indicates that strain-free states extend throughout the high-temperature grown GaN layers

Development of equipment for in situ studies of biofilm in hot water systems

DEFF Research Database (Denmark)

Bagh, Lene Karen; Albrechtsen, Hans-Jørgen; Arvin, Erik

1999-01-01

New equipment was developed for in situ studies of biofilms in hot water tanks and hot water pipes under normal operation and pressure. Sampling ports were installed in the wall of a hot water tank and through these operating shafts were inserted with a test plug in the end. The surface of the test...

First-principle natural band alignment of GaN / dilute-As GaNAs alloy

Directory of Open Access Journals (Sweden)

Chee-Keong Tan

2015-01-01

Full Text Available Density functional theory (DFT calculations with the local density approximation (LDA functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions...

Introduction of radiation protection and dosimetry in new hot cell facility in research center Rez

International Nuclear Information System (INIS)

Svrcula, P.; Petrickova, A.; Srba, O.; Miklos, M.; Svoboda, P.

2015-01-01

The purpose of the poster is to present radiation protection and dosimetry in the new hot cell facility being constructed as part of the SUSEN project. The hot cell facility is composed of 10 hot cells and 1 semi-hot cell. All shielding is made from steel, the outer wall shielding has thickness of 500 mm, internal wall between hot cells 300 mm with the possibility to extension to 500 mm. The ceiling shielding has a thickness of 400 mm and the floor shielding is 300 mm wide. Shielded windows allow direct view into the hot cells. Their shielding effect is equivalent to 500 mm of steel. The dimension of the window in the control room is 800 mm x 600 mm with a thickness of 900 mm. All important operating data are collected in the central system of hot cells. The system monitors under-pressure level and temperature in each chamber. If necessary it can directly control the ventilation system. Each hot cell is equipped with dose rate probes. The system also measures and evaluates airborne radioactivity in the building

Surface state of GaN after rapid-thermal-annealing using AlN cap-layer

Energy Technology Data Exchange (ETDEWEB)

El-Zammar, G., E-mail: georgio.elzammar@univ-tours.fr [Université François Rabelais, Tours, GREMAN, CNRS UMR 7347, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France); Khalfaoui, W. [Université François Rabelais, Tours, GREMAN, CNRS UMR 7347, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France); Oheix, T. [Université François Rabelais, Tours, GREMAN, CNRS UMR 7347, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France); STMicroelectronics, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France); Yvon, A.; Collard, E. [STMicroelectronics, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France); Cayrel, F.; Alquier, D. [Université François Rabelais, Tours, GREMAN, CNRS UMR 7347, 10 rue Thalès de Milet CS 97155, 37071 Tours Cedex 2 (France)

2015-11-15

Graphical abstract: Surface state of a crack-free AlN cap-layer reactive sputtered on GaN and annealed at high temperature showing a smooth, pit-free surface. - Highlights: • We deposit a crystalline AlN layer by reactive magnetron sputtering on GaN. • We show the effect of deposition parameters of AlN by reactive magnetron sputtering on the quality of the grown layer. • We demonstrate the efficiency of double cap-layer for GaN protection during high temperature thermal treatments. • We show an efficient selective etch of AlN without damaging GaN surface. - Abstract: Critical issues need to be overcome to produce high performance Schottky diodes on gallium nitride (GaN). To activate dopant, high temperature thermal treatments are required but damage GaN surface where hexagonal pits appear and prevent any device processing. In this paper, we investigated the efficiency of cap-layers on GaN during thermal treatments to avoid degradation. Aluminum nitride (AlN) and silicon oxide (SiO{sub x}) were grown on GaN by direct current reactive magnetron sputtering and plasma-enhanced chemical vapor deposition, respectively. AlN growth parameters were studied to understand their effect on the grown layers and their protection efficiency. Focused ion beam was used to measure AlN layer thickness. Crystalline quality and exact composition were verified using X-ray diffraction and energy dispersive X-ray spectroscopy. Two types of rapid thermal annealing at high temperatures were investigated. Surface roughness and pits density were evaluated using atomic force microscopy and scanning electron microscopy. Cap-layers wet etching was processed in H{sub 3}PO{sub 4} at 120 °C for AlN and in HF (10%) for SiO{sub x}. This work reveals effective protection of GaN during thermal treatments at temperatures as high as 1150 °C. Low surface roughness was obtained. Furthermore, no hexagonal pit was observed on the surface.

Single phase semipolar (11 anti 22) GaN on (10 anti 10) sapphire

Energy Technology Data Exchange (ETDEWEB)

Ploch, S.; Stellmach, J.; Schwaner, T.; Frentrup, M.; Wernicke, T.; Pristovsek, M.; Kneissl, M. [Institute of Solid States Physics, (Germany); Park, J.B.; Niermann, T.; Lehmann, M. [Institute of Optics and Atomic Physics, TU Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)

2011-07-01

InGaN quantum well based light emitters grown on (0001) GaN suffer from poor quantum efficiencies with increasing indium mole fraction due to strong polarization fields along the polar crystal orientation. This effect can be greatly reduced by growing on semi- and non-polar GaN orientations. Semipolar (11 anti 22) GaN layers were deposited by metalorganic vapour phase epitaxy on (10 anti 10) sapphire. After sapphire substrate nitridation at 1000 C, a GaN nucleation layer was deposited at high temperature, followed by the deposition of 1.5 nm thick GaN buffer layers. The samples show predominantly (11 anti 22) orientation with a small fraction of (10 anti 13) oriented domains. With increasing nitridation layer thickness the (10 anti 13) phase is suppressed leading to a very smooth surface morphology (rms roughness < 4nm). PL measurements show dominant basel plane stacking fault (BSF) I{sub 1} luminescence without any other defects. Transmission electron microscopy measurements reveal a high BSF density. The FWHM of the X-ray diffraction rocking curve measurements of the (1122) reflection decreases to 1193 arcsec and 739 arcsec along [1 anti 100] and [11 anti 23] respectively with increasing nucleation temperature. Using high temperature nucleation smooth and homogeneous (11 anti 22) phase GaN layers have been obtained.

Cyclic voltammetry response of an undoped CVD diamond electrodes

Energy Technology Data Exchange (ETDEWEB)

Fabisiak, K., E-mail: kfab@ukw.edu.pl [Institute of Physics, Kazimierz Wielki University, Powstancow Wielkopolskich 2, 85-090 Bydgoszcz (Poland); Torz-Piotrowska, R. [Faculty of Chemical Technology and Engineering, UTLS Seminaryjna 3, 85-326 Bydgoszcz (Poland); Staryga, E. [Institute of Physics, Technical University of Lodz, Wolczanska 219, 90-924 Lodz (Poland); Szybowicz, M. [Faculty of Technical Physics, Poznan University of Technology, Nieszawska 13A, 60-965 Poznan (Poland); Paprocki, K.; Popielarski, P.; Bylicki, F. [Institute of Physics, Kazimierz Wielki University, Powstancow Wielkopolskich 2, 85-090 Bydgoszcz (Poland); Wrzyszczynski, A. [Institute of Physics, Technical University of Lodz, Wolczanska 219, 90-924 Lodz (Poland)

2012-09-01

Highlights: Black-Right-Pointing-Pointer Correlation was found between diamond quality and its electrochemical performance. Black-Right-Pointing-Pointer The electrode sensitivity depends on the content of sp{sup 2} carbon phase in diamond layer. Black-Right-Pointing-Pointer The sp{sup 2} carbon phase content has little influence on the CV peak separation ({Delta}E{sub p}). - Abstract: The polycrystalline undoped diamond layers were deposited on tungsten wire substrates by using hot filament chemical vapor deposition (HFCVD) technique. As a working gas the mixture of methanol in excess of hydrogen was used. The morphologies and quality of as-deposited films were monitored by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy respectively. The electrochemical activity of the obtained diamond layers was monitored by using cyclic voltammetry measurements. Analysis of the ferrocyanide-ferricyanide couple at undoped diamond electrode suggests that electrochemical reaction at diamond electrode has a quasireversibile character. The ratio of the anodic and cathodic peak currents was always close to unity. In this work we showed that the amorphous carbon admixture in the CVD diamond layer has a crucial influence on its electrochemical performance.

Influence of in-situ deposited SiNx interlayer on crystal quality of GaN epitaxial films

Science.gov (United States)

Fan, Teng; Jia, Wei; Tong, Guangyun; Zhai, Guangmei; Li, Tianbao; Dong, Hailiang; Xu, Bingshe

2018-05-01

GaN epitaxial films with SiNx interlayers were prepared by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The influences of deposition times and locations of SiNx interlayers on crystal quality of GaN epitaxial films were studied. Under the optimal growth time of 120 s for the SiNx interlayer, the dislocation density of GaN film is reduced to 4.05 × 108 cm-2 proved by high resolution X-ray diffraction results. It is found that when the SiNx interlayer deposits on the GaN nucleation islands, the subsequent GaN film has the lowest dislocation density of only 2.89 × 108 cm-2. Moreover, a model is proposed to illustrate the morphological evolution and associated propagation processes of TDs in GaN epi-layers with SiNx interlayers for different deposition times and locations.

Uniform GaN thin films grown on (100) silicon by remote plasma atomic layer deposition

International Nuclear Information System (INIS)

Shih, Huan-Yu; Chen, Miin-Jang; Lin, Ming-Chih; Chen, Liang-Yih

2015-01-01

The growth of uniform gallium nitride (GaN) thin films was reported on (100) Si substrate by remote plasma atomic layer deposition (RP-ALD) using triethylgallium (TEG) and NH 3 as the precursors. The self-limiting growth of GaN was manifested by the saturation of the deposition rate with the doses of TEG and NH 3 . The increase in the growth temperature leads to the rise of nitrogen content and improved crystallinity of GaN thin films, from amorphous at a low deposition temperature of 200 °C to polycrystalline hexagonal structures at a high growth temperature of 500 °C. No melting-back etching was observed at the GaN/Si interface. The excellent uniformity and almost atomic flat surface of the GaN thin films also infer the surface control mode of the GaN thin films grown by the RP-ALD technique. The GaN thin films grown by RP-ALD will be further applied in the light-emitting diodes and high electron mobility transistors on (100) Si substrate. (paper)

CVD diamond detectors and dosimeters

International Nuclear Information System (INIS)

Manfredotti, C.; Fizzotti, F.; LoGiudice, A.; Paolini, C.; Oliviero, P.; Vittone, E.; Torino Univ., Torino

2002-01-01

Natural diamond, because of its well-known properties of tissue-equivalence, has recorded a wide spreading use in radiotherapy planning with electron linear accelerators. Artificial diamond dosimeters, as obtained by Chemical Vapour Deposition (CVD) could be capable to offer the same performances and they can be prepared in different volumes and shapes. The dosimeter sensitivity per unit volume may be easily proved to be better than standard ionization microchamber. We have prepared in our laboratory CVD diamond microchamber (diamond tips) in emispherical shape with an external diameter of 200 μm, which can be used both as X-ray beam profilometers and as microdosimeters for small field applications like stereotaxy and also for in vivo applications. These dosimeters, which are obtained on a wire substrate that could be either metallic or SiC or even graphite, display good performances also as ion or synchrotron X-rays detectors

Morphology of self-catalyzed GaN nanowires and chronology of their formation by molecular beam epitaxy

International Nuclear Information System (INIS)

Galopin, E; Largeau, L; Patriarche, G; Travers, L; Glas, F; Harmand, J C

2011-01-01

GaN nanowires are synthesized by plasma-assisted molecular beam epitaxy on Si(111) substrates. The strong impact of the cell orientation relative to the substrate on the nanowire morphology is shown. To study the kinetics of growth, thin AlN markers are introduced periodically during NW growth. These markers are observed in single nanowires by transmission electron microscopy, giving access to the chronology of the nanowire formation and to the time evolution of the nanowire morphology. A long delay precedes the beginning of nanowire formation. Then, their elongation proceeds at a constant rate. Later, shells develop on the side-wall facets by ascending growth of layer bunches which first agglomerate at the nanowire foot.

Economic assessment of single-walled carbon nanotube processes

Science.gov (United States)

Isaacs, J. A.; Tanwani, A.; Healy, M. L.; Dahlben, L. J.

2010-02-01

The carbon nanotube market is steadily growing and projected to reach 1.9 billion by 2010. This study examines the economics of manufacturing single-walled carbon nanotubes (SWNT) using process-based cost models developed for arc, CVD, and HiPco processes. Using assumed input parameters, manufacturing costs are calculated for 1 g SWNT for arc, CVD, and HiPco, totaling 1,906, 1,706, and 485, respectively. For each SWNT process, the synthesis and filtration steps showed the highest costs, with direct labor as a primary cost driver. Reductions in production costs are calculated for increased working hours per day and for increased synthesis reaction yield (SRY) in each process. The process-based cost models offer a means for exploring opportunities for cost reductions, and provide a structured system for comparisons among alternative SWNT manufacturing processes. Further, the models can be used to comprehensively evaluate additional scenarios on the economics of environmental, health, and safety best manufacturing practices.

Economic assessment of single-walled carbon nanotube processes

Energy Technology Data Exchange (ETDEWEB)

Isaacs, J. A., E-mail: jaisaacs@coe.neu.ed [Northeastern University, NSF Center for High-rate Nanomanufacturing (United States); Tanwani, A. [Infojini Solutions Inc. (United States); Healy, M. L. [Babcock Power Inc. (United States); Dahlben, L. J. [Northeastern University, NSF Center for High-rate Nanomanufacturing (United States)

2010-02-15

The carbon nanotube market is steadily growing and projected to reach $1.9 billion by 2010. This study examines the economics of manufacturing single-walled carbon nanotubes (SWNT) using process-based cost models developed for arc, CVD, and HiPco processes. Using assumed input parameters, manufacturing costs are calculated for 1 g SWNT for arc, CVD, and HiPco, totaling $1,906, $1,706, and $485, respectively. For each SWNT process, the synthesis and filtration steps showed the highest costs, with direct labor as a primary cost driver. Reductions in production costs are calculated for increased working hours per day and for increased synthesis reaction yield (SRY) in each process. The process-based cost models offer a means for exploring opportunities for cost reductions, and provide a structured system for comparisons among alternative SWNT manufacturing processes. Further, the models can be used to comprehensively evaluate additional scenarios on the economics of environmental, health, and safety best manufacturing practices.

Rare earth point defects in GaN

Energy Technology Data Exchange (ETDEWEB)

Sanna, S.

2007-12-14

In this work we investigate rare earth doped GaN, by means of theoretical simulations. The huge unit cells necessary to model the experimental system, where dilute amount of rare earth ions are used, are handled with the charge self consistent density-functional based-tight binding (SCC-DFTB) calculational scheme. The method has been extended to include LDA+U and simplified self interaction corrected (SIC)-like potentials for the simulation of systems with localised and strongly correlated electrons. A set of tight-binding parameters has been created to model the interaction of GaN with some dopants, including a selection of lanthanide ions interesting due to their optical or magnetic properties (Pr, Eu, Gd, Er and Tm). The f-electrons were treated as valence electrons. A qualitatively correct description of the band gap is crucial for the simulation of rare earth doped GaN, because the luminescence intensity of the implanted samples depends on the size of the host band gap and because the rare earths could introduce charge transition levels near the conduction band. In this work these levels are calculated with the Slater-Janak (SJ) transition state model, which allows an approximate calculation of the charge transition levels by analysing the Kohn-Sham eigenvalues of the DFT. (orig.)

Fabrication of GaN with buried tungsten (W) structures using epitaxial lateral overgrowth (ELO) via LP-MOVPE

International Nuclear Information System (INIS)

Miyake, Hideto; Yamaguchi, Motoo; Haino, Masahiro

2000-01-01

A buried tungsten (W) mask structure with GaN is successfully obtained by epitaxial lateral overgrowth (ELO) technique via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The selectivity of GaN growth on the window region vs. the mask region is good. An underlying GaN with a striped W metal mask is easily decomposed above 500 C by the W catalytic effect, by which radical hydrogen is reacted with GaN. It is difficult to bury the W mask because severe damage occurs in the GaN epilayer under the mask. It is found that an underlying AlGaN/GaN layer with a narrow W stripe mask width (mask/window - 2/2 microm) leads the ELO GaN layer to be free from damage, resulting in an excellent W-buried structure

Effect of different electrolytes on porous GaN using photo-electrochemical etching

Energy Technology Data Exchange (ETDEWEB)

Al-Heuseen, K., E-mail: kalhussen@yahoo.com [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Hashim, M.R. [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Ali, N.K. [Material Innovations and Nanoelectronics Research Group, Faculty of Electrical Engineering, Department of Electronic Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor (Malaysia)

2011-05-01

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E{sub 2} (high), A{sub 1} (LO), A{sub 1} (TO) and E{sub 2} (low). There was a red shift in E{sub 2} (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H{sub 2}SO{sub 4}:H{sub 2}O{sub 2} and KOH followed by the samples etched in HF:HNO{sub 3} and in HF:C{sub 2}H{sub 5}OH.

Effect of different electrolytes on porous GaN using photo-electrochemical etching

International Nuclear Information System (INIS)

Al-Heuseen, K.; Hashim, M.R.; Ali, N.K.

2011-01-01

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E 2 (high), A 1 (LO), A 1 (TO) and E 2 (low). There was a red shift in E 2 (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H 2 SO 4 :H 2 O 2 and KOH followed by the samples etched in HF:HNO 3 and in HF:C 2 H 5 OH.

Effect of different electrolytes on porous GaN using photo-electrochemical etching

Science.gov (United States)

Al-Heuseen, K.; Hashim, M. R.; Ali, N. K.

2011-05-01

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E 2 (high), A 1 (LO), A 1 (TO) and E 2 (low). There was a red shift in E 2 (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H 2SO 4:H 2O 2 and KOH followed by the samples etched in HF:HNO 3 and in HF:C 2H 5OH.

Hexagonal (wurtzite) GaN inclusions as a defect in cubic (zinc-blende) GaN

International Nuclear Information System (INIS)

Zainal, N.; Novikov, S.V.; Akimov, A.V.; Staddon, C.R.; Foxon, C.T.; Kent, A.J.

2012-01-01

The dependence of the hexagonal fraction with thickness in MBE-grown bulk cubic (c-) GaN epilayer is presented in this paper. A number of c-GaN epilayers with different thicknesses were characterized via PL and XRD measurements. From the PL spectra, the signal due to h-GaN inclusions increases as the thickness of the c-GaN increases. On the contrary, in the XRD diffractogram, c-GaN shows a dominant signal at all thicknesses, and only a weak peak at ∼35° is observed in the diffractogram, implying the existence of a small amount of h-GaN in the c-GaN layer. The best quality of c-GaN is observed in the first 10 μm of GaN on the top of GaAs substrate. Even though the hexagonal content increases with the thickness, the average content remains below 20% in c-GaN layers up to 50 μm thick. The surface morphology of thick c-GaN is also presented.

Rarefied gas flow in a rectangular enclosure induced by non-isothermal walls

Energy Technology Data Exchange (ETDEWEB)

Vargas, Manuel; Tatsios, Giorgos; Valougeorgis, Dimitris, E-mail: diva@mie.uth.gr [Department of Mechanical Engineering, University of Thessaly, 38334 Volos (Greece); Stefanov, Stefan [Institute of Mechanics, Bulgarian Academy of Sciences, Sofia (Bulgaria)

2014-05-15

The flow of a rarefied gas in a rectangular enclosure due to the non-isothermal walls with no synergetic contributions from external force fields is investigated. The top and bottom walls are maintained at constant but different temperatures and along the lateral walls a linear temperature profile is assumed. Modeling is based on the direct numerical solution of the Shakhov kinetic equation and the Direct Simulation Monte Carlo (DSMC) method. Solving the problem both deterministically and stochastically allows a systematic comparison and verification of the results as well as the exploitation of the numerical advantages of each approach in the investigation of the involved flow and heat transfer phenomena. The thermally induced flow is simulated in terms of three dimensionless parameters characterizing the problem, namely, the reference Knudsen number, the temperature ratio of the bottom over the top plates, and the enclosure aspect ratio. Their effect on the flow configuration and bulk quantities is thoroughly examined. Along the side walls, the gas flows at small Knudsen numbers from cold-to-hot, while as the Knudsen number is increased the gas flows from hot-to-cold and the thermally induced flow configuration becomes more complex. These flow patterns with the hot-to-cold flow to be extended to the whole length of the non-isothermal side walls may exist even at small temperature differences and then, they are enhanced as the temperature difference between the top and bottom plates is increased. The cavity aspect ratio also influences this flow configuration and the hot-to-cold flow is becoming more dominant as the depth compared to the width of the cavity is increased. To further analyze the flow patterns a novel solution decomposition into ballistic and collision parts is introduced. This is achieved by accordingly modifying the indexing process of the typical DSMC algorithm. The contribution of each part of the solution is separately examined and a physical

GaN quantum dots: from basic understanding to unique applications

International Nuclear Information System (INIS)

Pelekanos, N T; Dialynas, G E; Simon, J; Mariette, H; Daudin, B

2005-01-01

The GaN self-assembled quantum dots constitute a very special and intriguing type of semiconductor nanostructure, mainly because they carry in their structure a giant internal electric field that can reach a value up to 7 MV/cm. In this report, we review the most important structural and optical properties of GaN quantum dots, and we discuss their advantages and limitations for blue-UV optoelectronic applications. (invited paper)

Recent results on CVD diamond radiation sensors

Science.gov (United States)

Weilhammer, P.; Adam, W.; Bauer, C.; Berdermann, E.; Bogani, F.; Borchi, E.; Bruzzi, M.; Colledani, C.; Conway, J.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; v. d. Eijk, R.; van Eijk, B.; Fallou, A.; Fish, D.; Fried, M.; Gan, K. K.; Gheeraert, E.; Grigoriev, E.; Hallewell, G.; Hall-Wilton, R.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Kass, R.; Knopfle, K. T.; Krammer, M.; Manfredi, P. F.; Meier, D.; LeNormand; Pan, L. S.; Pernegger, H.; Pernicka, M.; Plano, R.; Re, V.; Riester, J. L.; Roe, S.; Roff; Rudge, A.; Schieber, M.; Schnetzer, S.; Sciortino, S.; Speziali, V.; Stelzer, H.; Stone, R.; Tapper, R. J.; Tesarek, R.; Thomson, G. B.; Trawick, M.; Trischuk, W.; Turchetta, R.; RD 42 Collaboration

1998-02-01

CVD diamond radiation sensors are being developed for possible use in trackers in the LHC experiments. The diamond promises to be radiation hard well beyond particle fluences that can be tolerated by Si sensors. Recent results from the RD 42 collaboration on charge collection distance and on radiation hardness of CVD diamond samples will be reported. Measurements with diamond tracking devices, both strip detectors and pixel detectors, will be discussed. Results from beam tests using a diamond strip detector which was read out with fast, 25 ns shaping time, radiation-hard pipeline electronics will be presented.

GaN quantum dot polarity determination by X-ray photoelectron diffraction

Czech Academy of Sciences Publication Activity Database

Romanyuk, Olexandr; Bartoš, Igor; Brault, J.; De Mierry, P.; Paskova, T.; Jiříček, Petr

2016-01-01

Roč. 389, Dec (2016), s. 1156-1160 ISSN 0169-4332 R&D Projects: GA ČR GA15-01687S; GA MŠk LM2015088 Institutional support: RVO:68378271 Keywords : GaN * semipolar GaN * quantum dots * X-ray photoelectron diffraction * surface polarity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.387, year: 2016

Thermal degradation of ohmic contacts on semipolar (11-22) GaN films grown on m-plane (1-100) sapphire substrates

International Nuclear Information System (INIS)

Kim, Doo Soo; Kim, Deuk Young; Seo, Yong Gon; Kim, Ji Hoon; Hwang, Sung Min; Baik, Kwang Hyeon

2012-01-01

Semipolar (11-22) GaN films were grown on m-plane (1-100) sapphire substrates by using metalorganic chemical vapor deposition. The line widths of the omega rocking curves of the semipolar GaN films were 498 arcsec along the [11-23] GaN direction and 908 arcsec along the [10-10] GaN direction. The properties of the Ti/Al/Ni/Au metal contact were investigated using transmission-line-method patterns oriented in both the [11-23] GaN and the [10-10] GaN directions of semipolar (11-22) GaN. The minimum specific contact resistance of ∼3.6 x 10 -4 Ω·cm -2 was obtained on as-deposited metal contacts. The Ohmic contact properties of semipolar (11-22) GaN became degraded with increasing annealing temperature above 400 .deg. C. The thermal degradation of the metal contacts may be attributed to the surface property of N-polarity on the semipolar (11-22) GaN films. Also, the semipolar (11-22) GaN films did not show clear anisotropic behavior of the electrical properties for different azimuthal angles.

Reynolds number invariance of the structure inclination angle in wall turbulence.

Science.gov (United States)

Marusic, Ivan; Heuer, Weston D C

2007-09-14

Cross correlations of the fluctuating wall-shear stress and the streamwise velocity in the logarithmic region of turbulent boundary layers are reported over 3 orders of magnitude change in Reynolds number. These results are obtained using hot-film and hot-wire anemometry in a wind tunnel facility, and sonic anemometers and a purpose-built wall-shear stress sensor in the near-neutral atmospheric surface layer on the salt flats of Utah's western desert. The direct measurement of fluctuating wall-shear stress in the atmospheric surface layer has not been available before. Structure inclination angles are inferred from the cross correlation results and are found to be invariant over the large range of Reynolds number. The findings justify the prior use of low Reynolds number experiments for obtaining structure angles for near-wall models in the large-eddy simulation of atmospheric surface layer flows.

Origin, state of the art and some prospects of the diamond CVD

CERN Document Server

Spitsyn, B V; Alexenko, A E

2000-01-01

A short review on the diamond CVD origin, together with its state of the art and some prospects was given. New hybrid methods of the diamond CVD permit to gain 1.2 to 6 times of growth rate in comparison with ordinary diamond CVD's. Recent results on n-type diamond film synthesis through phosphorus doping in the course of the CVD process are briefly discussed. In comparison with high-pressure diamond synthesis, the CVD processes open new facets of the diamond as ultimate crystal for science and technology evolution. It was stressed that, mainly on the basis of new CVDs of diamond, the properties of natural diamond are not only reproduced, but can be surpassed. As examples, mechanical (fracture resistance), physical (thermal conductivity), and chemical (oxidation stability) properties are mentioned. Some present issues in the field are considered.

Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p-type GaN by Mg doping followed by low-energy electron beam irradiation

Energy Technology Data Exchange (ETDEWEB)

Amano, Hiroshi [Department of Electrical Engineering and Computer Science, Venture Business Laboratory, Akasaki Research Center, Nagoya University (Japan)

2015-06-15

This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid to late 1980s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Growth of GaN Layers on Sapphire by Low-Temperature-Deposited Buffer Layers and Realization of p-type GaN by Magesium Doping and Electron Beam Irradiation (Nobel Lecture).

Science.gov (United States)

Amano, Hiroshi

2015-06-26

This Review is a personal reflection on the research that led to the development of a method for growing gallium nitride (GaN) on a sapphire substrate. The results paved the way for the development of smart display systems using blue LEDs. The most important work was done in the mid to late 80s. The background to the author's work and the process by which the technology that enables the growth of GaN and the realization of p-type GaN was established are reviewed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

Science.gov (United States)

Su, Ming; Chen, Chingchi; Rajan, Siddharth

2013-07-01

GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600-1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles.

High quality self-separated GaN crystal grown on a novel nanoporous template by HVPE.

Science.gov (United States)

Huo, Qin; Shao, Yongliang; Wu, Yongzhong; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

2018-02-16

In this study, a novel nanoporous template was obtained by a two-step etching process from MOCVD-GaN/Al 2 O 3 (MGA) with electrochemical etching sequentially followed by chemical wet etching. The twice-etched MOCVD-GaN/Al 2 O 3 (TEMGA) templates were utilized to grow GaN crystals by hydride vapor phase epitaxy (HVPE) method. The GaN crystals were separated spontaneously from the TEMGA template with the assistance of voids formed by the etched nanopores. Several techniques were utilized to characterize the quality of the free-standing GaN crystals obtained from the TEMGA template. Results showed that the quality of the as-obtained GaN crystals was improved obviously compared with those grown on the MGA. This convenient technique can be applied to grow high-quality free-standing GaN crystals.

Photoassisted Kelvin probe force microscopy at GaN surfaces: The role of polarity

Science.gov (United States)

Wei, J. D.; Li, S. F.; Atamuratov, A.; Wehmann, H.-H.; Waag, A.

2010-10-01

The behavior of GaN surfaces during photoassisted Kelvin probe force microscopy is demonstrated to be strongly dependant on surface polarity. The surface photovoltage of GaN surfaces illuminated with above-band gap light is analyzed as a function of time and light intensity. Distinct differences between Ga-polar and N-polar surfaces could be identified, attributed to photoinduced chemisorption of oxygen during illumination. These differences can be used for a contactless, nondestructive, and easy-performable analysis of the polarity of GaN surfaces.

Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

International Nuclear Information System (INIS)

Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu

2016-01-01

GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer. (paper)

Synthesis of carbon nanotubes by CVD method using iron and molybdenum-based catalysts supported on ceramic matrices;Sintese de nanotubos de carbono por CVD utilizando catalisadores a base de ferro e molibdenio suportados em matrizes ceramicas

Energy Technology Data Exchange (ETDEWEB)

Teixeira, Ana Paula de Carvalho

2010-07-01

Molybdenum is known for its synergistic effect in the synthesis of carbon nanotubes (CNs) by chemical vapor deposition (CVD method). When added to typical catalysts like iron, nickel, and cobalt, even in small quantities, it is increases the yield of these nanostructures. The presence of Mo also has an influence on the type and number of CN walls formed. Although this effect is widely documented in the literature, there is not yet a consensus about the mechanism of action of molybdenum in catalytic systems. The objective of the present work is to study the influence of molybdenum on the catalytic activity of iron nanoparticle-based catalysts supported on magnesium oxide (Fe/MgO system) in the synthesis of carbon nanotubes by the CVD method. The Mo concentration was systematically varied from null to molar ratio values four times greater than the quantity of Fe, and the obtained material (catalysts and carbon nanotubes) were broadly characterized by different techniques. In order to also study the influence of the preparation method on the final composition of the catalytic system phases, the catalytic systems (Fe/MgO e FeMo{sub x}/MgO) were synthesized by two different methods: co-precipitation and impregnation. The greatest CN yields were observed for the catalysts prepared by coprecipitation. The difference was attributed to better dispersion of the Fe and Mo phases in the catalyst ceramic matrix. In the precipitation stage, it was observed the formation of layered double hydroxides whose concentration increased with the Mo content up to the ratio of Mo/Fe equal to 0.2. This phase is related to a better distribution of Fe and Mo in this concentration range. Another important characteristic observed is that the ceramic matrix is not inert. It can react both with Fe and Mo and form the iron solid solution in the magnesium oxide and the phases magnesium-ferrite (MgFe{sub 2}0{sub 4}) and magnesium molybdate (MgMo0{sub 4}). The MgFe{sub 2}0{sub 4} phase is observed in

Incorporation of Mg in Free-Standing HVPE GaN Substrates

Science.gov (United States)

Zvanut, M. E.; Dashdorj, J.; Freitas, J. A.; Glaser, E. R.; Willoughby, W. R.; Leach, J. H.; Udwary, K.

2016-06-01

Mg, the only effective p-type dopant for nitrides, is well studied in thin films due to the important role of the impurity in light-emitting diodes and high-power electronics. However, there are few reports of Mg in thick free-standing GaN substrates. Here, we demonstrate successful incorporation of Mg into GaN grown by hydride vapor-phase epitaxy (HVPE) using metallic Mg as the doping source. The concentration of Mg obtained from four separate growth runs ranged between 1016 cm-3 and 1019 cm-3. Raman spectroscopy and x-ray diffraction revealed that Mg did not induce stress or perturb the crystalline quality of the HVPE GaN substrates. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies were performed to investigate the types of point defects in the crystals. The near-band-edge excitonic and shallow donor-shallow acceptor radiative recombination processes involving shallow Mg acceptors were prominent in the PL spectrum of a sample doped to 3 × 1018 cm-3, while the EPR signal was also thought to represent a shallow Mg acceptor. Detection of this signal reflects minimization of nonuniform strain obtained in the thick free-standing HVPE GaN compared with heteroepitaxial thin films.

X-ray determination of strain in ion implanted GaN

International Nuclear Information System (INIS)

Qadri, S.B.; Molnar, B.; Yousuf, M.; Carosella, C.A.

2002-01-01

The out-of-plane c, and in-plane a, lattice parameters of wurtzite gallium nitride (GaN) films, grown on the [0 0 0 1] basal plane of sapphire have been determined and the impact of ion implantation having dose between 5x10 13 and 5x10 15 cm -2 investigated. The thickness of the GaN layers was in the 1-3.5 μm range. The overall effect of the (0 0 0 1) GaN growth on (0 0 0 1) sapphire is biaxial compression in wurtzite α-GaN. Earlier X-ray studies have indicated that the films of GaN grow either purely in α-GaN phase or in α-GaN phase with a cubic β-GaN component. In contrast, our high-resolution X-ray diffraction (XRD) measurement revealed two isostructural polymorphs of α-GaN phases having different lattice parameters. Influence of ion implantation is to increase the values of lattice parameters a and c and could be rationalized in terms of an increase in the defects. At doses above 5x10 15 cm -2 , XRD analysis indicates the existence of an amorphous layer preventing the determination of a and c accurately

Reduced MLH3 Expression in the Syndrome of Gan-Shen Yin Deficiency in Patients with Different Diseases.

Science.gov (United States)

Du, Juan; Zhong, Maofeng; Liu, Dong; Liang, Shufang; Liu, Xiaolin; Cheng, Binbin; Zhang, Yani; Yin, Zifei; Wang, Yuan; Ling, Changquan

2017-01-01

Traditional Chinese medicine formulates treatment according to body constitution (BC) differentiation. Different constitutions have specific metabolic characteristics and different susceptibility to certain diseases. This study aimed to assess the characteristic genes of gan-shen Yin deficiency constitution in different diseases. Fifty primary liver cancer (PLC) patients, 94 hypertension (HBP) patients, and 100 diabetes mellitus (DM) patients were enrolled and classified into gan-shen Yin deficiency group and non-gan-shen Yin deficiency group according to the body constitution questionnaire to assess the clinical manifestation of patients. The mRNA expressions of 17 genes in PLC patients with gan-shen Yin deficiency were different from those without gan-shen Yin deficiency. However, considering all patients with PLC, HBP, and DM, only MLH3 was significantly lower in gan-shen Yin deficiency group than that in non-gen-shen Yin deficiency. By ROC analysis, the relationship between MLH3 and gan-shen Yin deficiency constitution was confirmed. Treatment of MLH3 (-/- and -/+) mice with Liuweidihuang wan, classical prescriptions for Yin deficiency, partly ameliorates the body constitution of Yin deficiency in MLH3 (-/+) mice, but not in MLH3 (-/-) mice. MLH3 might be one of material bases of gan-shen Yin deficiency constitution.

Selective CVD tungsten on silicon implanted SiO/sub 2/

International Nuclear Information System (INIS)

Hennessy, W.A.; Ghezzo, M.; Wilson, R.H.; Bakhru, H.

1988-01-01

The application range of selective CVD tungsten is extended by its coupling to the ion implantation of insulating materials. This article documents the results of selective CVD tungsten using silicon implanted into SiO/sub 2/ to nucleate the tungsten growth. The role of implant does, energy, and surface preparation in achieving nucleation are described. SEM micrographs are presented to demonstrate the selectivity of this process. Measurements of the tungsten film thickness and sheet resistance are provided for each of the experimental variants corresponding to successful deposition. RBS and XPS analysis are discussed in terms of characterizing the tungsten/oxide interface and to evaluate the role of the silicon implant in the CVD tungsten mechanism. Utilizing this method a desired metallization pattern can be readily defined with lithography and ion implantation, and accurately replicated with a layer of CVD tungsten. This approach avoids problems usually associated with blanket deposition and pattern transfer, which are particularly troublesome for submicron VLSI technology

Prediction of wall shear stresses in transitional boundary layers using near-wall mean velocity profiles

International Nuclear Information System (INIS)

Jeon, Woo Pyung; Shin, Sung Ho; Kang, Shin Hyoung

2000-01-01

The local wall shear stress in transitional boundary layer was estimated from the near-wall mean velocity data using the principle of Computational Preston tube Method(CPM). The previous DNS and experimental databases of transitional boundary layers were used to demonstrate the accuracy of the method and to provide the applicable range of wall unit y + . The skin friction coefficients predicted by the CPM agreed well with those from previous studies. To reexamine the applicability of the CPM, near-wall hot-wire measurements were conducted in developing transitional boundary layers on a flat plate with different freestream turbulence intensities. The intermittency profiles across the transitional boundary layers were reasonably obtained from the conditional sampling technique. An empirical correlation between the representative intermittency near the wall and the free parameter K 1 of the extended wall function of CPM has been newly proposed using the present and other experimental data. The CPM has been verified as a useful tool to measure the wall shear stress in transitional boundary layer with reasonable accuracy

Carrier confinement effects of InxGa1-xN/GaN multi quantum disks with GaN surface barriers grown in GaN nanorods

Science.gov (United States)

Park, Youngsin; Chan, Christopher C. S.; Taylor, Robert A.; Kim, Nammee; Jo, Yongcheol; Lee, Seung W.; Yang, Woochul; Im, Hyunsik

2018-04-01

Structural and optical properties of InxGa1-xN/GaN multi quantum disks (QDisks) grown on GaN nanorods by molecular beam epitaxy have been investigated by transmission electron microscopy and micro-photoluminescence (PL) spectroscopy. Two types of InGaN QDisks were grown: a pseudo-3D confined InGaN pillar-type QDisks embedded in GaN nanorods; and QDisks in flanged cone type GaN nanorods. The PL emission peak and excitation dependent PL behavior of the pillar-type Qdisks differ greatly from those of the flanged cone type QDisks. Time resolved PL was carried out to probe the differences in charge carrier dynamics. The results suggest that by constraining the formation of InGaN QDisks within the centre of the nanorod, carriers are restricted from migrating to the surface, decreasing the surface recombination at high carrier densities.

Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

Directory of Open Access Journals (Sweden)

Kunook Chung

2014-09-01

Full Text Available We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto SiO2/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metal–organic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance light-emitting diodes (LEDs, were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGa1–xN/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation.

Effects of Light Intensity Activity on CVD Risk Factors: A Systematic Review of Intervention Studies

Directory of Open Access Journals (Sweden)

Romeo B. Batacan

2015-01-01

Full Text Available The effects of light intensity physical activity (LIPA on cardiovascular disease (CVD risk factors remain to be established. This review summarizes the effects of LIPA on CVD risk factors and CVD-related markers in adults. A systematic search of four electronic databases (PubMed, Academic Search Complete, SPORTDiscus, and CINAHL examining LIPA and CVD risk factors (body composition, blood pressure, glucose, insulin, glycosylated hemoglobin, and lipid profile and CVD-related markers (maximal oxygen uptake, heart rate, C-reactive protein, interleukin-6, tumor necrosis factor-alpha, and tumor necrosis factor receptors 1 and 2 published between 1970 and 2015 was performed on 15 March 2015. A total of 33 intervention studies examining the effect of LIPA on CVD risk factors and markers were included in this review. Results indicated that LIPA did not improve CVD risk factors and CVD-related markers in healthy individuals. LIPA was found to improve systolic and diastolic blood pressure in physically inactive populations with a medical condition. Reviewed studies show little support for the role of LIPA to reduce CVD risk factors. Many of the included studies were of low to fair study quality and used low doses of LIPA. Further studies are needed to establish the value of LIPA in reducing CVD risk.

Influence of Si-doping on heteroepitaxially grown a-plane GaN

Energy Technology Data Exchange (ETDEWEB)

Wieneke, Matthias; Bastek, Barbara; Noltemeyer, Martin; Hempel, Thomas; Rohrbeck, Antje; Witte, Hartmut; Veit, Peter; Blaesing, Juergen; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-Universitaet Magdeburg, FNW/IEP, Universitaetsplatz 2, 39106 Magdeburg (Germany)

2011-07-01

Si-doped a-plane GaN samples with nominal doping levels up to 10{sup 20} cm{sup -3} were grown on r-plane sapphire by metal organic vapor phase epitaxy. Silane flow rates higher than 59 nmol/min lead to three dimensional grown crystallites as revealed by scanning electron microscopy. High resolution X-ray diffraction, photoluminescence and cathodoluminescence suggest considerably reduced defect densities in the large micrometer-sized GaN crystallites. Especially, transmission electron microscopy images verify a very low density of basal plane stacking faults less than 10{sup 4} cm{sup -1} in these crystallites consisting of heteroepitaxially grown a-plane GaN. In our presentation the influence of the Si doping on the basal plane stacking faults will be discussed.

Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

International Nuclear Information System (INIS)

Su, Ming; Chen, Chingchi; Rajan, Siddharth

2013-01-01

GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600–1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles. (invited review)

Undoped p-type GaN1-xSbx alloys: Effects of annealing

Science.gov (United States)

Segercrantz, N.; Baumgartner, Y.; Ting, M.; Yu, K. M.; Mao, S. S.; Sarney, W. L.; Svensson, S. P.; Walukiewicz, W.

2016-12-01

We report p-type behavior for undoped GaN1-xSbx alloys with x ≥ 0.06 grown by molecular beam epitaxy at low temperatures (≤400 °C). Rapid thermal annealing of the GaN1-xSbx films at temperatures >400 °C is shown to generate hole concentrations greater than 1019 cm-3, an order of magnitude higher than typical p-type GaN achieved by Mg doping. The p-type conductivity is attributed to a large upward shift of the valence band edge resulting from the band anticrossing interaction between localized Sb levels and extended states of the host matrix.

High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

DEFF Research Database (Denmark)

Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong

2003-01-01

Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while...... the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 ( 7) and 319 ( 10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phases were found to have very similar bulk moduli [ 208...

Dominant intrinsic acceptors in GaN and ZnO

Energy Technology Data Exchange (ETDEWEB)

Saarinen, K; Hautakangas, S; Tuomisto, F [Laboratory of Physics, Helsinki University of Technology, PO Box 1100, FI-02015 TKK (Finland)

2006-09-01

Positron annihilation measurements reveal negatively charged Ga vacancies in n-type GaN and Zn vacancies in n-type ZnO. Positron trapping at other negative defects is not observed, indicating that cation vacancies are the dominant acceptors in these materials. The vacancy concentrations are the same as the total acceptor densities determined in Hall experiments, confirming the dominant role of the vacancy defects. The Ga vacancy in GaN is found as the main compensating centre over the range of four orders of magnitude of intentional oxygen doping.

Dominant intrinsic acceptors in GaN and ZnO

International Nuclear Information System (INIS)

Saarinen, K; Hautakangas, S; Tuomisto, F

2006-01-01

Positron annihilation measurements reveal negatively charged Ga vacancies in n-type GaN and Zn vacancies in n-type ZnO. Positron trapping at other negative defects is not observed, indicating that cation vacancies are the dominant acceptors in these materials. The vacancy concentrations are the same as the total acceptor densities determined in Hall experiments, confirming the dominant role of the vacancy defects. The Ga vacancy in GaN is found as the main compensating centre over the range of four orders of magnitude of intentional oxygen doping

Thermoelastic Stress Field Investigation of GaN Material for Laser Lift-off Technique based on Finite Element Method

International Nuclear Information System (INIS)

Ting, Wang; Zhan-Zhong, Cui; Li-Xin, Xu

2009-01-01

The transient thermoelastic stress fields of GaN films is analyzed by the finite element method for the laser lift-off (LLO) technique. Stress distributions in GaN films irradiated by pulse laser with different energy densities as functions of time and depth are simulated. The results show that the high thermoelastic stress distributions in GaN films localize within about 1 μm below the GaN/Al 2 O 3 interface using proper laser parameters. It is also found that GaN films can avoid the thermal deformation because the maximum thermoelastic stress 4.28 GPa is much smaller than the yield strength of GaN 15GPa. The effects of laser beam dimension and the thickness of GaN films on stress distribution are also analyzed. The variation range of laser beam dimension as a function of the thickness of GaN films is simulated to keep the GaN films free of thermal deformation. LLO experiments are also carried out. GaN-based light-emitting diodes (LEDs) are separated from sapphire substrates using the parameters obtained from the simulation. Compared with devices before LLO, P–I–V measurements of GaN-based LEDs after LLO show that the electrical and optical characteristics improve greatly, indicating that no stress damage is brought to GaN films using proper parameters obtained by calculation during LLO

Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

Science.gov (United States)

Buckeridge, J; Catlow, C R A; Scanlon, D O; Keal, T W; Sherwood, P; Miskufova, M; Walsh, A; Woodley, S M; Sokol, A A

2015-01-09

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Determination of the Nitrogen Vacancy as a Shallow Compensating Center in GaN Doped with Divalent Metals

Science.gov (United States)

Buckeridge, J.; Catlow, C. R. A.; Scanlon, D. O.; Keal, T. W.; Sherwood, P.; Miskufova, M.; Walsh, A.; Woodley, S. M.; Sokol, A. A.

2015-01-01

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p -type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Science.gov (United States)

Zhang, Jingzhao; Zhang, Yiou; Tse, Kinfai; Zhu, Junyi

2018-01-01

Heterostructures of wurtzite based devices have attracted great research interest because of the tremendous success of GaN in light emitting diodes (LED) industry. High-quality GaN thin films on inexpensive and lattice matched ZnO substrates are both commercially and technologically desirable. Intrinsic wetting conditions, however, forbid such heterostructures as the energy of ZnO polar surfaces is much lower than that of GaN polar surfaces, resulting in 3D growth mode and poor crystal quality. Based on first-principles calculations, we propose the use of surfactant hydrogen to dramatically alter the growth mode of the heterostructures. Stable H-involved surface configurations and interfaces are investigated with the help of our newly developed modelling techniques. The temperature and chemical potential dependence of our proposed strategy, which is critical in experiments, is predicted by applying the experimental Gibbs free energy of H2. Our thermodynamic wetting condition analysis is a crucial step for the growth of GaN on ZnO, and we find that introducing H will not degrade the stability of ZnO substrate. This approach will allow the growth of high-quality GaN thin films on ZnO substrates. We believe that our new strategy may reduce the manufactory cost, improve the crystal quality, and improve the efficiency of GaN-based devices.

Recent results with CVD diamond trackers

Energy Technology Data Exchange (ETDEWEB)

Adam, W.; Bauer, C.; Berdermann, E.; Bergonzo, P.; Bogani, F.; Borchi, E.; Brambilla, A.; Bruzzi, M.; Colledani, C.; Conway, J.; Dabrowski, W.; Delpierre, P.; Deneuville, A.; Dulinski, W.; Eijk, B. van; Fallou, A.; Fizzotti, F.; Foulon, F.; Friedl, M.; Gan, K.K.; Gheeraert, E.; Grigoriev, E.; Hallewell, G.; Hall-Wilton, R.; Han, S.; Hartjes, F.; Hrubec, J.; Husson, D.; Kagan, H.; Kania, D.; Kaplon, J.; Karl, C.; Kass, R.; Knoepfle, K.T.; Krammer, M.; Logiudice, A.; Lu, R.; Manfredi, P.F.; Manfredotti, C.; Marshall, R.D.; Meier, D.; Mishina, M.; Oh, A.; Pan, L.S.; Palmieri, V.G.; Pernicka, M.; Peitz, A.; Pirollo, S.; Polesello, P.; Pretzl, K.; Procario, M.; Re, V.; Riester, J.L.; Roe, S.; Roff, D.; Rudge, A.; Runolfsson, O.; Russ, J.; Schnetzer, S.; Sciortino, S.; Speziali, V.; Stelzer, H.; Stone, R.; Suter, B.; Tapper, R.J.; Tesarek, R.; Trawick, M.; Trischuk, W.; Vittone, E.; Walsh, A.M.; Wedenig, R.; Weilhammer, P.; White, C.; Ziock, H.; Zoeller, M

1999-08-01

We present recent results on the use of Chemical Vapor Deposition (CVD) diamond microstrip detectors for charged particle tracking. A series of detectors was fabricated using 1 x 1 cm{sup 2} diamonds. Good signal-to-noise ratios were observed using both slow and fast readout electronics. For slow readout electronics, 2 {mu}s shaping time, the most probable signal-to-noise ratio was 50 to 1. For fast readout electronics, 25 ns peaking time, the most probable signal-to-noise ratio was 7 to 1. Using the first 2 x 4 cm{sup 2} diamond from a production CVD reactor with slow readout electronics, the most probable signal-to-noise ratio was 23 to 1. The spatial resolution achieved for the detectors was consistent with the digital resolution expected from the detector pitch.

Recent results with CVD diamond trackers

CERN Document Server

Adam, W; Berdermann, E; Bergonzo, P; Bogani, F; Borchi, E; Brambilla, A; Bruzzi, Mara; Colledani, C; Conway, J; Dabrowski, W; Delpierre, P A; Deneuville, A; Dulinski, W; van Eijk, B; Fallou, A; Fizzotti, F; Foulon, F; Friedl, M; Gan, K K; Gheeraert, E; Grigoriev, E; Hallewell, G D; Hall-Wilton, R; Han, S; Hartjes, F G; Hrubec, Josef; Husson, D; Kagan, H; Kania, D R; Kaplon, J; Karl, C; Kass, R; Knöpfle, K T; Krammer, Manfred; Lo Giudice, A; Lü, R; Manfredi, P F; Manfredotti, C; Marshall, R D; Meier, D; Mishina, M; Oh, A; Pan, L S; Palmieri, V G; Pernicka, Manfred; Peitz, A; Pirollo, S; Polesello, P; Pretzl, Klaus P; Procario, M; Re, V; Riester, J L; Roe, S; Roff, D G; Rudge, A; Runólfsson, O; Russ, J; Schnetzer, S R; Sciortino, S; Speziali, V; Stelzer, H; Stone, R; Suter, B; Tapper, R J; Tesarek, R J; Trawick, M L; Trischuk, W; Vittone, E; Walsh, A M; Wedenig, R; Weilhammer, Peter; White, C; Ziock, H J; Zöller, M

1999-01-01

We present recent results on the use of chemical vapor deposition (CVD) diamond microstrip detectors for charged particle tracking. A series of detectors was fabricated using 1*1 cm/sup 2/ diamonds. Good signal-to-noise ratios were observed using both slow and fast readout electronics. For slow readout electronics, 2 mu s shaping time, the most probable signal-to-noise ratio was 50 to 1. For fast readout electronics, 25 ns peaking time, the most probable signal-to-noise ratio was 7 to 1. Using the first 2*4 cm/sup 2/ diamond from a production CVD reactor with slow readout electronics, the most probable signal-to-noise ratio was 23 to 1. The spatial resolution achieved for the detectors was consistent with the digital resolution expected from the detector pitch. (6 refs).

Energetics and magnetism of Co-doped GaN(0001) surfaces: A first-principles study

International Nuclear Information System (INIS)

Qin, Zhenzhen; Xiong, Zhihua; Chen, Lanli; Qin, Guangzhao

2014-01-01

A comprehensive first-principles study of the energetics, electronic, and magnetic properties of Co-doped GaN(0001) thin films are presented and the effect of surface structure on the magnetic coupling between Co atoms is demonstrated. It is found that Co atoms prefer to substitute the surface Ga sites in different growth conditions. In particular, a CoN/GaN interface structure with Co atoms replacing the first Ga layer is preferred under N-rich and moderately Ga-rich conditions, while CoGa x /GaN interface is found to be energetically stable under extremely Ga-rich conditions. It is worth noted that the antiferromagnetic coupling between Co atoms is favorable in clean GaN(0001) surface, but the existence of ferromagnetism would be expected to occur as Co concentration increased in Ga-bilayer GaN(0001) surface. Our study provides the theoretical understanding for experimental research on Co-doped GaN films and might promise the Co:GaN system potential applications in spin injection devices

Infrared Reflectance Analysis of Epitaxial n-Type Doped GaN Layers Grown on Sapphire.

Science.gov (United States)

Tsykaniuk, Bogdan I; Nikolenko, Andrii S; Strelchuk, Viktor V; Naseka, Viktor M; Mazur, Yuriy I; Ware, Morgan E; DeCuir, Eric A; Sadovyi, Bogdan; Weyher, Jan L; Jakiela, Rafal; Salamo, Gregory J; Belyaev, Alexander E

2017-12-01

Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n + /n 0 /n + -GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

Fabrication and PL of Al-doped gallium nitride nanowires

International Nuclear Information System (INIS)

Zhou Shaomin

2006-01-01

Mass Al-doped GaN nanowires with an average diameter of about 50 nm and lengths up to several millimeters are fabricated by a CVD approach. The as-fabricated products have a single crystal phase and grow along the direction. The growth of Al-doped GaN nanowires is suggested for quasi-vapor-solid mechanism (QVSM). In particular, for as large-scale GaN nanowires, a novel strong ultraviolet PL spectrum (from 3.3 to 3.7 eV) appears with a doping Al where the Al-doped GaN nanowires are found to be responsible for the different characteristics; the PL mechanism is explained in detail

''Cube-on-hexagon'' orientation relationship for Fe on GaN(0001): The missing link in bcc/hcp epitaxy

International Nuclear Information System (INIS)

Gao Cunxu; Brandt, Oliver; Laehnemann, Jonas; Jahn, Uwe; Jenichen, Bernd; Schoenherr, Hans-Peter; Erwin, Steven C.

2010-01-01

We investigate, experimentally and theoretically, the epitaxy of body-centered-cubic Fe on hexagonal GaN. For growth on the Ga-polar GaN(0001) surface we find the well-known Pitsch-Schrader orientation relationship between Fe and GaN. On the N-polar GaN(0001) surface we observe coexistence between the familiar Burgers orientation and a new orientation in which the Fe(001) plane is parallel to GaN(0001). This 'cube-on-hexagon' orientation constitutes the high-symmetry link required for constructing a symmetry diagram for bcc/hcp systems in which all orientation relationships are connected by simple rotations.

Theoretical investigation of electronic, magnetic and optical properties of Fe doped GaN thin films

International Nuclear Information System (INIS)

Salmani, E.; Mounkachi, O.; Ez-Zahraouy, H.; Benyoussef, A.; Hamedoun, M.; Hlil, E.K.

2013-01-01

Highlights: •Magnetic and optical properties Fe-doped GaN thin films are studied using DFT. •The band gaps of GaN thin films are larger than the one of the bulk. •The layer thickness and acceptor defect can switch the magnetic ordering. -- Abstract: Using first principles calculations based on spin-polarized density functional theory, the magnetic and optical properties of GaN and Fe-doped GaN thin films with and without acceptor defect is studied. The band structure calculations show that the band gaps of GaN thin films with 2, 4 and 6 layers are larger than the one of the bulk with wurtzite structure and decreases with increasing the film thickness. In Fe doped GaN thin films, we show that layer of thickness and acceptor defect can switch the magnetic ordering from disorder local moment (DLM) to ferromagnetic (FM) order. Without acceptor defect Fe doped GaN exhibits spin glass phase in 4 layers form and ferromagnetic state for 2 layers form of the thin films, while it exhibits ferromagnetic phase with acceptor defect such as vacancies defect for 2 and 4 layers. In the FM ordering, the thin films is half-metallic and is therefore ideal for spin application. The different energy between ferromagnetic state and disorder local moment state was evaluated. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities

GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

Science.gov (United States)

Hashida, Ryohei; Sasaki, Takashi; Hane, Kazuhiro

2018-03-20

Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510 nm in thickness, 1000 nm in width, and a clad of 240 nm in thickness. A GaN crystalline layer of 1000 nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300 nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7  dB/mm around a wavelength of 1.55 μm. The microring radii ranged from 30 to 60 μm, where the measured free-spectral ranges varied from 2.58 to 5.30 nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.

A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications

Science.gov (United States)

Jia, Hujun; Luo, Yehui; Wu, Qiuyuan; Yang, Yintang

2017-11-01

In this paper, a novel GaN HEMT with high efficiency-energy characteristic is proposed. Different from the conventional structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate. The key idea in this work is to improve the microwave output characteristics. The simulated results show that the drain saturation current and peak transconductance of DRBL GaN HEMT is slightly decreased, the transconductance saturation flatness is increased by 0.5 V and the breakdown voltage is also enhanced too. Due to the both recessed barrier layer, the gate-drain/gate-source capacitance is decreased by 6.3% and 11.3%, respectively. The RF simulated results show that the maximum oscillation frequency for DRBL GaN HEMT is increased from 57 GHz to 64 GHz and the saturation power density is 8.7 W/mm at 600 MHz, 6.9 W/mm at 1200 MHz with the higher power added efficiency (PAE). Further investigation show that DRBL GaN HEMT can achieve to 6.4 W/mm and the maximum PAE 83.8% at 2400 MHz. Both are higher than the 5.0 W/mm and 80.3% for the conventional structure. When the operating frequency increases to X band, the DRBL GaN HEMT still exhibits the superior output performances. All the results show that the advantages and the potential capacities of DRBL GaN HEMT at high efficiency-energy are greater than the conventional GaN HEMT.

From Stable ZnO and GaN Clusters to Novel Double Bubbles and Frameworks

Directory of Open Access Journals (Sweden)

Matthew R. Farrow

2014-05-01

Full Text Available A bottom up approach is employed in the design of novel materials: first, gas-phase “double bubble” clusters are constructed from high symmetry, Th, 24 and 96 atom, single bubbles of ZnO and GaN. These are used to construct bulk frameworks. Upon geometry optimization—minimisation of energies and forces computed using density functional theory—the symmetry of the double bubble clusters is reduced to either C1 or C2, and the average bond lengths for the outer bubbles are 1.9 Å, whereas the average bonds for the inner bubble are larger for ZnO than for GaN; 2.0 Å and 1.9 Å, respectively. A careful analysis of the bond distributions reveals that the inter-bubble bonds are bi-modal, and that there is a greater distortion for ZnO. Similar bond distributions are found for the corresponding frameworks. The distortion of the ZnO double bubble is found to be related to the increased flexibility of the outer bubble when composed of ZnO rather than GaN, which is reflected in their bulk moduli. The energetics suggest that (ZnO12@(GaN48 is more stable both in gas phase and bulk frameworks than (ZnO12@(ZnO48 and (GaN12@(GaN48. Formation enthalpies are similar to those found for carbon fullerenes.

Vacancy-type defects in Al2O3/GaN structure probed by monoenergetic positron beams

Science.gov (United States)

Uedono, Akira; Nabatame, Toshihide; Egger, Werner; Koschine, Tönjes; Hugenschmidt, Christoph; Dickmann, Marcel; Sumiya, Masatomo; Ishibashi, Shoji

2018-04-01

Defects in the Al2O3(25 nm)/GaN structure were probed by using monoenergetic positron beams. Al2O3 films were deposited on GaN by atomic layer deposition at 300 °C. Temperature treatment above 800 °C leads to the introduction of vacancy-type defects in GaN due to outdiffusion of atoms from GaN into Al2O3. The width of the damaged region was determined to be 40-50 nm from the Al2O3/GaN interface, and some of the vacancies were identified to act as electron trapping centers. In the Al2O3 film before and after annealing treatment at 300-900 °C, open spaces with three different sizes were found to coexist. The density of medium-sized open spaces started to decrease above 800 °C, which was associated with the interaction between GaN and Al2O3. Effects of the electron trapping/detrapping processes of interface states on the flat band voltage and the defects in GaN were also discussed.

Changes in CVD risk factors in the activity counseling trial

Directory of Open Access Journals (Sweden)

Meghan Baruth

2011-01-01

Full Text Available Meghan Baruth1, Sara Wilcox1, James F Sallis3, Abby C King4,5, Bess H Marcus6, Steven N Blair1,21Department of Exercise Science, 2Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Public Health Research Center, Columbia, SC, USA; 3Department of Psychology, San Diego State University, San Diego, CA, USA; 4Department of Health Research and Policy, 5Stanford Prevention Research Center, Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA; 6Behavioral and Social Sciences Section, Brown University Program in Public Health, Providence, RI, USAAbstract: Primary care facilities may be a natural setting for delivering interventions that focus on behaviors that improve cardiovascular disease (CVD risk factors. The purpose of this study was to examine the 24-month effects of the Activity Counseling Trial (ACT on CVD risk factors, to examine whether changes in CVD risk factors differed according to baseline risk factor status, and to examine whether changes in fitness were associated with changes in CVD risk factors. ACT was a 24-month multicenter randomized controlled trial to increase physical activity. Participants were 874 inactive men and women aged 35–74 years. Participants were randomly assigned to one of three arms that varied by level of counseling, intensity, and resource requirements. Because there were no significant differences in change over time between arms on any of the CVD risk factors examined, all arms were combined, and the effects of time, independent of arm, were examined separately for men and women. Time × Baseline risk factor status interactions examined whether changes in CVD risk factors differed according to baseline risk factor status. Significant improvements in total cholesterol, high-density lipoprotein cholesterol (HDL-C and low-density lipoprotein cholesterol, the ratio of total cholesterol to HDL-C, and triglycerides were seen in

Radiation sensors based on GaN microwires

Science.gov (United States)

Verheij, D.; Peres, M.; Cardoso, S.; Alves, L. C.; Alves, E.; Durand, C.; Eymery, J.; Lorenz, K.

2018-05-01

GaN microwires were shown to possess promising characteristics as building blocks for radiation resistant particle detectors. They were grown by metal organic vapour phase epitaxy with diameters between 1 and 2 μm and lengths around 20 μm. Devices were fabricated by depositing gold contacts at the extremities of the wires using photolithography. The response of these single wire radiation sensors was then studied under irradiation with 2 MeV protons. Severe degradation of the majority of devices only sets in for fluences above protons cm‑2 revealing good radiation resistance. During proton irradiation, a clear albeit small current gain was observed with a corresponding decay time below 1 s. Photoconductivity measurements upon irradiation with UV light were carried out before and after the proton irradiation. Despite a relatively low gain, attributed to significant dark currents caused by a high dopant concentration, fast response times of a few seconds were achieved comparable to state-of-the-art GaN nanowire photodetectors. Irradiation and subsequent annealing resulted in an overall improvement of the devices regarding their response to UV radiation. The photocurrent gain increased compared to the values that were obtained prior to the irradiation, without compromising the decay times. The results indicate the possibility of using GaN microwires not only as UV detectors, but also as particle detectors.

Chemical vapour deposition of silicon under reduced pressure in a hot-wall reactor: Equilibrium and kinetics

International Nuclear Information System (INIS)