bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion-Implanted GaN/AlGaN/GaN HEMTs with Extremely Low Gate Leakage Current
Authors: Nomoto Kazuki , Tajima Taku , Mishima Tomoyoshi , Satoh Masataka , Nakamura Tohru 
Published: April 2011

ABSTRACTWe demonstrate the realization of compatibility of extremely low gate leakage current and low source resistance with Si ion-implanted (I/I) GaN/AlGaN/GaN surface-stabilized high-electron mobility transistor (HEMT) without any recess etching process. The source/drain regions were formed using Si ion implantation into undoped GaN/AlGaN/GaN on sapphire substrate. Using ion implantation into source/drain (S/D) regions with energy of 80 keV, the performances were significantly improved. On-resistance (Ron) reduced from 105 to 9.2 Ω·mm. Saturation drain current (Idss) and maximum transconductance (gmMAX) increased from 49 to 527 mA/mm and from 13 to 84 mS/mm (Vg=+1V).
Low-Temperature Cathodoluminescence Mapping of Green, Blue, and UV GaInN/GaN LED Dies
Authors: Xia Yong , Detchprohm Theeradetch , Senawiratne Jayantha , Li Yufeng , Zhao Wei , Zhu Mingwei , Wetzel Christian 
Published: April 2011

ABSTRACTGaInN based light emitting diodes (LEDs) play an important role as energy efficient light sources in solid state lighting. A controversial discussion addresses the origin of lateral light emission variations and their correlation with either of the identified defects, e.g., threading dislocations and V-defects. In order to establish any possible correlation of defects and luminescence centers, we analyze three UV, blue and green LED dies by microscopic mapping of spectroscopic cathodoluminescence and secondary electrons at variable low temperature from 7 K to room temperature. Particular effort is being placed on a quantitative analysis of the luminescence signal. Image intensities are not being scaled and offset for highest contrast as otherwise typical for imaging mode. In standard configuration, we analyze image areas of (0.037 mm)2 with pixel resolution of 72 nm. Following regions of strong and weak emission we find that remain bright and dark respectively even at low temperature. Those variations increase with the mean emission wavelength of the LEDs and with temperature. The largest peak wavelength variation associated with the intensity contrast was observed in the green LEDs and amounts to 5 nm. Here the peak wavelength is higher in the dark spots than in the bright ones. This finding corresponds to the general trend when comparing the lower efficiency in longer wavelength green emitters to the blue ones.
Fabrication of AlGaN/GaN HFET with a High Breakdown Voltage on 4-inch Si (111) Substrate by MOVPE
Authors: Niiyama Yuki , Kato Sadahiro , Sato Yoshihiro , Iwami Masayuki , Li Jiang , Takehara Hironari , Kambayashi Hiroshi , Ikeda Nariaki , Yoshida Seikoh 
Published: April 2011

ABSTRACTWe investigated an AlGaN/GaN heterostructure field effect transistor (HFET) on Si substrates using a multi-wafer metalorganic vapor phase epitaxy (MOVPE) system. It was confirmed that a GaN film with smooth surface and without any crack was obtained. To increase a resistance of a GaN buffer layer, the carbon (C) -doping was carried out by controlling the V/III ratio and the growth pressure. The breakdown voltage of the buffer layer was dramatically improved by introducing the C. As a result, the breakdown voltage was about 900 V when the C concentration was about ∼8×1018 cm−3. After while, an AlGaN/GaN heterojunction FET (HFET) on a C-doped GaN buffer layer was fabricated. We achieved the breakdown voltage of over 1000 V and the maximum drain current of over 150 mA/mm, respectively. It was found that the C doped buffer layer is very effective for improving the breakdown voltage of AlGaN/GaN HFETs.
Electronic Structures of Heavily Boron-doped Superconducting Diamond Films
Authors: Yokoya Takayoshi , Okazaki Hiroyuki , Nakamura Tetsuya , Matsushita Tomohiro , Muro Takayuki , Ikenaga Eiji , Kobata Masaaki , Kobayashi Keisuke , Takeuchi Akihisa , Awaji Akihiro , Takano Yoshihiko , Nagao Masanori , Takenouchi Tomohiro , Kawarada Hiroshi , Oguchi Tamio 
Published: April 2011

ABSTRACTRecent photoemission studies on heavily boron-doped superconducting diamond films, reporting the electronic structure evolution as a function of boron concentrations, are reviewed. From soft X-ray angle-resolved photoemission spectroscopy, which directly measures electronic band dispersions, depopulation of electrons (or formation of hole pockets) at the top of the valence band were clearly observed. This indicates that the holes at the top of the valence bands are responsible for the metallic properties and hence superconductivity at lower temperatures. Hard X-ray photoemission spectroscopy observed shift of the main C 1s core level and intensity evolution of a lower binding energy additional structure, suggesting chemical potential shift, carrier doping efficiency by boron doping, and possibility of boron-related cluster formations.
Electrical Transport in Heavily B-Doped Epitaxial Diamond and NCD
Authors: Nesladek Milos , Bergonzo Phillipe , Mares Jiri , Hubik Pavel 
Published: April 2011

ABSTRACTThis paper deals with a LT transport study in B-doped diamond. To understand the electrical transport in heavily B-doped diamond and the influence of disorder onto the electrical transport, we have prepared nanocrystalline and epitaxial B-doped diamond films at CEA Saclay. The transport properties of these layers have been studied at the Institute of Physics Czech Academy of Sciences in Prague. It has been found that our B-doped nanocrystalline diamond exhibits also the SC transition, similarly as the original Russian work done on HPHT polycrystals or single crystal diamond. Additionally, the properties of (111) epitaxial films are discussed.
Biological Applications of Nanocrystalline Diamond
Authors: Williams Oliver A. , Daenen Michael , Haenen Ken 
Published: April 2011

ABSTRACTNanocrystalline diamond films have generated substantial interest in recent years due to their low cost, extreme properties and wide application arena. Diamond is chemically inert, has a wide electrochemical window and is stable in numerous harsh environments. Nanocrystalline diamond has the advantage of being readily grown on a variety of substrates at very low thickness, resulting in smooth conformal coatings with high transparency. These films can be doped from highly insulating to metallically conductive and at very high concentrations become superconducting.
The effects of Methane Concentration on diamond nucleation and growth during bias enhanced nucleation on 3C-SiC(100) surfaces
Authors: Arnault Jean-Charles , Saada Samuel , Intiso Luciana , Bergonzo Philippe 
Published: April 2011

ABSTRACTThe methane effects on nucleation and growth of diamond during bias enhanced nucleation treatment have been studied on 3C-SiC (100) surfaces. At low methane concentration of 1%, no diamond nucleation was observed, whether at 3 %, nucleation density values as high as 4×1010/cm2 were reached. A further increase of the methane concentration up to 5% induces a significant enhancement of the diamond nucleation density that was observed only slightly higher at 7×1010/cm2. Moreover, the Field Emission Gun Scanning Electron Microscopy (FEG-SEM) pictures well emphasized that the methane content affects both the nucleation and growth mechanisms.
Nano Crystalline Diamond Synthesized by Hot Filament Chemical Vapor Deposition
Authors: Hirai Takayuki , Kanno Yoshinori , Takagi Yoshiki 
Published: April 2011

ABSTRACTDue to its extreme hardness, chemical and mechanical stability, large band gap and highest thermal conductivity, poly-crystalline diamond is expected to be an excellent packaging material for biomedical and environmental MEMS devices. Recently nano crystalline diamond (NCD) has been synthesized by microwave plasma chemical vapor deposition (MPCVD) technique using a gas mixture of methane-hydrogen or methane-hydrogen and inert gas, argon mixture. Diamond synthesis from liquid carbon source has a relatively high growth rate among various CVD methods. Hot filament chemical vapor deposition (HFCVD) is popular method in order to grow the diamond particles or films. The equipment of HFCVD in present paper is simple and the easy operating. Therefore we tried to NCD synthesis by HFCVD from liquid carbon source such as methanol, ethanol etc. The structure, surface morphology, and grain size of the diamond were examined with field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. We confirmed our diamond particles as NCD with typical Raman peak of NCD. And we observed 100nm under in diameter with FE-SEM. We will refer to NCD films synthesis by HFCVD in the paper.
Highly Oriented Diamond Films Grown at High Growth Rate
Authors: Li Xianglin , Collazo Ramon , Sitar Zlatko 
Published: April 2011

ABSTRACTHighly oriented diamond (HOD) films were grown at a high growth rate on (100) silicon substrates by microwave plasma chemical vapor deposition (MPCVD), following the standard bias-enhanced nucleation (BEN) process. The growth rate and diamond quality were investigated as a function of methane concentration in hydrogen (2-6%), and N2/CH4 ratio (0 to 0.12). A four-fold increase in the growth rate of HOD films and a three times faster expansion and coalescence of (100) facets was observed within the above process window. The films with the best quality were grown under an N2/CH4 ratio of 0.08 at methane concentration of 3.5%. The ratio of x-ray intensity between the first order twins and {111} poles was only 1%. A detailed study of the crystalline quality and phase purity as a function of methane concentration and nitrogen addition is presented.
Photoelectron Emission Mechanism From Hydrogen Terminated Nano-Crystalline Diamond
Authors: Takeuchi Daisuke , Saeki Kazuhiko , Nebel Christoph Erwin , Yamasaki Satoshi , Williams Oliver Aneurin 
Published: April 2011

ABSTRACTWe investigated the electron affinity on hydrogen-terminated nano- (NCD) and ultranano-crystalline diamond (UNCD) films to reveal influences of defects, sp2 and grain boundaries on photoemission properties. To compare properties, single crystalline IIa diamond, optical grade poly-, nano-, ultranano-crystalline diamond films, a diamond-like carbon film, a highly oriented pyrolytic graphite have been characterized. All hydrogen terminated SCD, PCD and NCD samples show continuous sub-band yield, arising at about 4.4 eV, regardless of their crystal and/or grain sizes, while UNCD, DLC, and HOPG do not show the specific photoemission in the regime hν < 6 eV. Note that the UNCD film grown with some amount of hydrogen in the gas phase (UNCD-H) shows a comparable yield spectrum as hydrogen-terminated SCD. According to the normalized spectra, obviously, the electron emission mechanism on hydrogen-terminated NCD films is the same as that of SCD with a NEA of -1.1 eV. The sub-band yield from NCD is even larger than that of SCD, which is attributed to surface enlargement.
Ultraviolet Photodetection Properties of ZnO Microtubes
Authors: Cheng Jiping , Fu Ming , Zhang Yunjin , Guo Ruyan 
Published: April 2011

ABSTRACTPhotodetectors based on wide-bandgap semiconductors have demonstrated several advantages over traditional ultraviolet (UV) detectors (photomultiplier tubes and Si-based UV detectors) such as low power consumption, high stability, and no need of other optical filters. ZnO stands a good chance of being a candidate material for solar-blind UV detection because of its direct bandgap of 3.37eV and high photoresponse. In this work, single crystal ZnO microtubes synthesized using a microwave-heating growth method and their UV photodetection properties were studied. The ZnO microtubes exhibited relatively fast UV photoresponse with a cut-off wavelength ∼370 nm, indicating their potential applications as high efficient and low cost UV detectors.
Modification of ZnO Layers by Molecular Adsorbates During Electrochemical Deposition
Authors: Loewenstein Thomas , Neumann Christian , Meyer Bruno K. , Yoshida Tsukasa , Schlettwein Derck 
Published: April 2011

ABSTRACTZnO and ZnO/EosinY hybrid materials were electrodeposited from aqueous zinc salt solutions on (0001) GaN and on (0001) ZnO. Crystalline ZnO was deposited as proven by X-ray diffraction (XRD). The intensity pattern for ZnO/EosinY showed a preferential orientation with the c- plane of ZnO parallel to GaN (0001) or ZnO (0001). XRD rocking curves with FWHM=0.25° indicated a high level of in-plane orientation of the deposited ZnO crystalline domains. The peak position of (0002) ZnO was shifted by 2Θ=1.3°. This difference and the corresponding simultaneous shift of (0004) ZnO were explained by a lattice expansion by 3.6 % in the c- direction. This clearly indicated the strong influence of the Eosin Y molecules adsorbed during the electrodeposition of ZnO. Scanning electron microscopy (SEM) revealed the formation of domains with different crystal sizes pointing at a varying density of nucleation sites on the substrate.
Growth and Characterization of Optical and Electrical Properties of ZnO Nano- and Microwires
Authors: Grundmann Marius , Rahm Andreas , Nobis Thomas , von Wenckstern Holger , Czekalla Christian , Lenzner Jörg , Lorenz Michael 
Published: April 2011

ABSTRACTZnO nanowires are readily fabricated with a novel and unique, high-pressure pulsed laser deposition process developed recently by us. It allows the flexible and reproducible control of morphology, diameter, lenght and composition. Furthermore, we report on the electrical characterization as well as stimulated emission from a zinc oxide (ZnO) microcrystals grown by carbothermal evaporation observed by spatially resolved photoluminescence (PL) and high excitation spectroscopy (HES).
Surface Luminescence of Polycrystalline Zinc Oxide Excited by Hydrogen Atoms
Authors: Sushchikh Michael , Styrov Vladislav , Tyutunnikov Vladimir , Cordella Nick 
Published: April 2011

ABSTRACTExcitation of a luminescence by highly exothermic chemical reaction on the surface of a luminophore provides a unique opportunity to separate surface luminescence from the bulk luminescence. This enables studies of the electronic properties of the semiconductor surfaces even if the surfaces are of complicate shapes. We have studied heterogeneous chemiluminescence (HCL) of ZnO powders. The luminescence was excited by a release of chemical energy, namely by catalytic recombination of hydrogen atoms. The HCL spectra were compared to the photoluminescence (PL) spectra. The HCL spectra were sensitive to the details of preparation and treatment whereas PL spectra almost did not change. HCL spectra of powder samples pretreated for enhancing “green” luminescence exhibited long-wavelength tail (up to 800 nm) and their maximum was blue-shifted as compared with PL spectra. Different HCL bands forming long-wavelength tail were isolated by changing the temperature of the samples. Additional milling of ZnO led to amplification of the HCL-specific surface bands. Pure ZnO showed neither PL nor HCL; however we were able to observe HCL surface bands with maxima at 610 nm and 730 nm after treatment of the sample in atomic hydrogen atmosphere at 570 K. Remarkably, such treatment did not cause appearance of the PL. The HCL in the presence of atomic hydrogen was steady in time and was caused by an abstraction of adsorbed hydrogen by incident hydrogen atoms, i.e. the reaction followed Eley-Rideal mechanism. The HCL can be utilized for in situ monitoring of the growth and evolution of ZnO in controlled atmosphere.
Controllable Synthesis of ZnO Nanorod Arrays via Simple Solution-Based Method
Authors: Charoensirithavorn Patcharee , Yoshikawa Susumu 
Published: April 2011

ABSTRACTHere we present a convenient solution-based method, which can afford a procedure to easily fabricate highly oriented ZnO nanorods on substrate at relatively low temperatures. The as-synthesized products have been characterized by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The results revealed that a densely packed and perpendicularly oriented single-crystalline ZnO nanorod arrays grew vertically on the fluorine-doped SnO2 transparent conducting oxide (FTO) glass substrates. In addition, we found that the length of the nanorod could be freely modified by controlling the solution temperature.
Visible Luminescence from ZnO Nanostructures
Authors: Cheng An-jen , Wang Dake , Seo Hee Won , Park Minseo , Tzeng Yonhua 
Published: April 2011

ABSTRACTRoom temperature photoluminescence (PL) spectra from zinc oxide (ZnO) nanostructures were studied. ZnO samples were produced via thermal chemical vapor deposition (thermal-CVD) and a variety of ZnO nanostructures were synthesized by adjusting the oxygen content during the growth process. All samples exhibit a sharp and strong ultra-violet near-band-edge (NBE) emission at about 3.18 eV. The visible emission from the samples deposited under an oxygen-deficient condition were dominated by blue-green band emission at 2.34 eV. The intensity of the blue-green band was greatly reduced (so-called green band free) for the ZnO deposited at the center of the wafer while strong violet-blue emission bands and broad bands at yellow-orange-red range were collected from the ZnO grown along the edge of the wafer. We believe that the spatial inhomogeniety was caused by turbulent gas flow in the reaction chamber, which resulted in different local oxygen concentration. Origin of visible luminescence from ZnO nanostructures will be discussed and a model to explain the observed visible luminescence process will be presented.
Schottky Contact Behaviour as a Function of Metal and ZnO Surface Polarity
Authors: Allen M.W. , Miller P. , Metson J.B. , Reeves R.J. , Alkaisi M.M. , Durbin S.M. 
Published: April 2011

ABSTRACTHall effect, photoluminescence (PL) and Schottky diode measurements were made on the Zn-polar , O-polar and m-plane faces of hydrothermally grown, bulk ZnO. Several polarity related differences were observed in the PL spectra. The most noticeable was increased emission from free excitons and from a triplet of emissions at 3.3725 - 3.3750 eV on the Zn-polar face. Polarity effects were also observed in the properties of highly rectifying, planar, silver oxide diodes fabricated by RF sputtering using an Ag target and an Ar/O2 plasma. The most significant of these was a consistent 130 meV larger barrier height for silver oxide diodes on the Zn-polar face compared to the O-polar face. These polarity effects are thought to result from the internal compensation of bound spontaneous polarization charges at the Zn-polar and O-polar faces. In addition, Au and Ag Schottky diodes with image-force-controlled ideality factors were achieved on the Zn-polar face of bulk ZnO without any special surface treatments.
Large Area Multi-wafer MOCVD of Transparent and Conducting ZnO Films
Authors: Tompa Gary S. , Sun S. , Provost L. G. , Mentel Dan , Sugrim D. , Chan Philip , Tong Keny , Wong Raymond , Lee A. 
Published: April 2011

ABSTRACTZnO thin films are of interest for an array of applications, including: light emitters, photovoltaics, sensors and transparent contacts, among others. Production routes for ZnO include sputtering, MBE and MOCVD. This paper focuses on our efforts to produce a large scale MOCVD thin film production tool and the results obtained from the reactor. Specifically, we have constructed a tool with a 16” wafer carrier that uniformly deposits ZnO films on 38×2” wafers simultaneously. The reactor operates at low pressure (<0.1 Atmosphere) and through 700°C. High quality, uniform films have been deposited on an array of substrates. Al-doped films exhibited resisitivities in the 1×10-3 ohm-cm range and transmissivity greater than 80%. Film morphology and crystallinity are a function of process parameters. The large area oxide MOCVD reactor design challenges and results are summarized. Tool performance and ZnO thin film quality are reviewed, as well as preliminary ZnO contact performance on GaN LEDs.
Electroplating of ZnO Nanowires Using Nanohole Arrays of Anodized Aluminum Oxide and Effects of Thermal Annealing
Authors: Ogata Ken-Ichi , Shingubara Shoso , Yorozu Hiromi , Nakanishi Tadahiko 
Published: April 2011

ABSTRACTElectroplating of ZnO nanowires was conducted using gold embedded anodized aluminum oxide (AAO) films on Si substrates. For electroplating, insulating layers at the bottom of AAO nanohole structures need to be removed. After electroplating, hexagonal structure of vertical ZnO nanowires was observed, however, they were broken and lied down by thermal annealing process. Photoluminescence (PL) spectra were investigated and that of post annealed ZnO nanowires indicates that nitrogen atoms were incorporated as acceptor.
ZnO Nanofibers Doped with Ga, In and Er Fabricated with Electrospinning Technique
Authors: Khan Aurangzeb , Jadwisienczak Wojciech M. , Khan Saima N. , Kordesch Martin E. 
Published: April 2011

ABSTRACTZnO nanofibers doped with Ga, In and Er metals have been fabricated by electrospinning technique. The diameter of the fibers was in the range of 0.5-2 μm and the length can be up to several feet. After spinning fabrication step the samples were dried out and annealed at 900 °C in air. Room temperature photoluminescence (PL) spectra measured for undoped and In- and Ga-doped ZnO fiber samples exhibit only a strong near band edge (NBE) emission at ∼380 nm with very weak green band at 525 nm. In contrary, the PL spectrum of Er-doped ZnO fibers shows a very weak NBE and strong green emission band at ∼550 nm at 300 K. The electrospinning mechanism used for the fabrication of nanofibers was found to be productive, simple and easy to implement disregarding of the doping type and concentration.
Lasing Characteristics of Nano-structured Zinc Oxide
Authors: Kuo Shou-Yi , Chen Wei-Chun , Lai Fang-I 
Published: April 2011

ABSTRACTHighy-quality nano-structured ZnO samples have been synthesized by simple chemical solution and post-thermal treatment. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), temperature-dependent photoluminescence (PL) spectra measurements. XRD patterns illustrated that there were no second phases in these ZnO samples, and the TEM results indicated that the ZnO samples are single crystalline with a hexagonal structure. Room-temperature PL spectra of ZnO thin films showed a strong UV near-band-edge (NBE) emission located at about 390 nm and a green defect-related (G) emissions, where the intensity ratio (INBE/IG) varies with the annealing temperatures. Meanwhile, the ZnO samples exhibited free exciton and very sharp exciton emissions at low temperatures. Particularly, room-temperature UV random lasing characteristic of ZnO films has been observed as well. It is shown that these nano-structured ZnO samples can exhibit random laser action depending on the growth condition. The threshold intensity for the lasing is comparable to earlier reported data. These results indicate that nano-structured ZnO samples prepared by simple techniques may be a promising material for further photonic devices. Possible lasing mechanism is discussed and further investigation to clarify the mechanism between the nano-structured ZnO samples is still underway.