bluuebunny/crossref_metadata_2025_split huggingface dataset:
Schottky I-V Characteristics of Au/Ni/GaN/SiNx nanonework/sapphire structures
Authors: Xie Jinqiao , Fu Yi , Morkoç Hadis 
Published: April 2011

ABSTRACTGaN layers on sapphire substrates were grown by metalorganic chemical vapor deposition using in situ porous SiNx nano-network. Crystalline quality of epilayers was characterized by X-ray rocking curve scans, and the full width at hall maximum values for (002) and (102) diffractions were improved from 252 arc sec and 405 arc sec, respectively, in control samples to 216 arc sec and 196 arc sec when SiNx was used. Ni/Au Schottky diodes (SDs) were fabricated and the SD performance was found to be critically dependent on the SiNx coverage (fewer and farther the pores the better the results) which is consistent with the trends of XRD and photoluminescence data. A 1.13eV barrier height was achieved when 5min SiNx layer was used compared with 0.78 eV without any SiNx nanonetwork. Furthermore, the breakdown voltage improved from 76 V to 250V when SiNx nanonetwork was used in otherwise identical structures.
Recessed Gate Processing for GaN/AlGaN-HEMTs
Authors: Pletschen Wilfried , Kiefer Rudolf , Raynor Brian , Mueller Stefan , Benkhelifa Foud , Quay Ruediger , Mikulla Michael , Schlechtweg Michael , Weimann Guenter 
Published: April 2011

ABSTRACTA dry etch process based on Cl2/SF6 has been developed to selectively remove GaN over AlGaN for the fabrication of recessed gate GaN/AlGaN HEMTs. Using this etching process recessed and non-recessed FETs were fabricated side by side on the same wafer to provide a fair comparision of data. Recessed gate FETs with a gatelength of 0.15μm show cutoff frequencies of 83 and more than 200 GHz for fT and fmax, respectively. Furthermore, gate-drain breakdown as high as 84V has been obtained which is more than twice as much compared to their non-recessed counterparts.
AlGaN/GaN High Electron Mobility Transistors on Si/SiO2/poly-SiC Substrates
Authors: Anderson Travis , Ren Fan , Voss Lars , Hlad Mark , Gila Brent P , Pearton Stephen , Covert Lance , Lin Jenshan , Thuret Julien , Lahreche H , Bove P 
Published: April 2011

ABSTRACTThe dc and rf performance of AlGaN/GaN High Electron Mobility Transistors (HEMTs) grown by Molecular Beam Epitaxy on Si-on-poly (SopSiC) substrates is reported. The HEMT structure incorporated a 7 period GaN/AlN superlattice between the AlGaN barrier and GaN channel for improved carrier confinement. The knee voltage of devices with 2 μm gate-drain spacing was 2.12 V and increased to 3 V at 8 μm spacing. The maximum frequency of oscillation, fMAX, was ∼40 GHz for devices with 0.5 μm gate length and 2 μm gate-drain spacing. Parameter extraction from the measured rf characteristics showed a maximum intrinsic transconductance of 143 mS.mm−1.
Enhancing Semiconductors with Diamond
Authors: Zimmer Jerry 
Published: April 2011

ABSTRACTIn the continuing thrust to extend Moore's law, silicon is beginning to confront several issues that require innovative materials solutions to increase transistor and interconnect speeds while dealing with the increasing thermal loads of advanced microprocessors. The unsurpassed thermal and mechanical properties of diamond can be profitably exploited to enhance the performance characteristics of silicon based circuits. The discussion focuses primarily on the integration of diamond with silicon for the manufacture of silicon on diamond (SOD) wafers for spreading heat from hot spots in microprocessors. Other interesting property combinations are also presented as food for thought regarding other possible enhancements to silicon device performance. Recent data and prognosis for the future will be presented.
Comparing the Young's Modulus of Near-Frictionless Carbon Films Obtained From Different Methods
Authors: Zhou Bo , Prorok Barton C. , Erdemir Ali , Eryilmaz O. 
Published: April 2011

ABSTRACTThe near-frictionless carbon (NFC) thin films grown at Argonne National Lab are excellent candidates for mitigating friction and wear issues in rotating and sliding MEMS applications. In this study, NFC films with Si/Si3N4 substrates were tested with static and CSM (continuous stiffness measurement) nanoindentation methods. Furthermore, the same NFC films with 900 nm thickness were fabricated into freestanding structures for the membrane deflection experiment (MDE). The Young's modulus obtained from these three methods were compared and contrasted. The E values obtained from the nanoindentation methods were nearly constant when the indent depth was less than 100 nm (1/10 of the film thickness). Both the static and CSM indentation data indicated a clear increasing trend of the Young's modulus with the indent depth until the elastic response from the substrate started to dominate the values (depth larger than 800 nm). The average modulus obtained from static and CSM nanoindentations were 49.5 ± 4.3 GPa and 50.2 ± 1.8 GPa for as-deposited films, respectively. The values changed to 46.9 ± 5.4 GPa and 46.8 ± 2.9 GPa after microfabrication processing. The larger standard deviation values indicated the affect of the increased surface roughness to the indentation tests. The E value determined from MDE tests was 35.1 ± 2.3 GPa, which was measurably smaller those from the indentation tests. As the AFM analysis showed little/no pile-up during indentation, the difference might come from the residual stress relief, which influences the measurement, when the NFC membranes were released from the substrate.
Attempts to p-Dope Ultrananocrystalline Diamond Films in a Hot Filament Reactor
Authors: May Paul William , Hannaway Matthew 
Published: April 2011

ABSTRACTUltrananocrystalline diamond (UNCD) films have been deposited using hot filament chemical vapour deposition using Ar/CH4/H2 gas mixtures plus additions of B2H6 in an attempt to make p-type semiconducting films. With increasing additions of B2H6 from 0 to 40,000 ppm with respect to C, the film growth rate was found to decrease substantially, whilst the individual grain sizes increased from nm to μm. With 40,000 ppm of B2H6, crystals of boric oxide were found on the substrate surface, which slowly hydrolysed to boric acid on exposure to air. These results are rationalised using a model for UNCD growth based on competition for surface radical sites between CH3 and C atoms.
Diamond Surface Modifications with Diazonium Salt
Authors: Uetsuka Hiroshi , Shin Dongchan , Tokuda Norio , Saeki Kazuhiko , Nebel Christoph E. 
Published: April 2011

ABSTRACTThe growth of covalently bonded nitrophenyl layers on atomically smooth boron-doped single crystalline diamond surfaces is characterized, using cyclic voltammetric attachment and constant potential grafting by electrochemical reduction of aryl diazonium salts. We apply atomic force microscopy (AFM) to characterize nitrophenyl layer-growth and thickness. Angle-resolved X-ray photoelectron spectroscopy is applied to reveal bonding arrangement of phenyl molecules and transient current measurements during the grafting is used to investigate the dynamics of chemical bonding. Nitrophenyl groups at an initial stage of attachment grown three-dimensional forming layers with varying heights and densities. Layer thicknesses of up to 80 Å are detected for cyclic voltammetry attachment after 5 cycles, whereas the layer becomes denser and only about 25 Å thick in case of constant potential attachment. No monomolecular closed layer could be detected. The data are discussed taking into account established growth models.
Irradiation-induced structural modifications in multifunctional nanocarbons
Authors: Gupta Sanju 
Published: April 2011

ABSTRACTSevere environmental tolerability is the prime factor in the development of novel space materials exhibiting excellent physical properties accompanied by lightweight, reusability, and multifunctional capabilities. Diamond is known for its reputation being radiation hard besides a range of outstanding properties (electronic, optical, mechanical, and chemical) and hence it is preferable in harsh environments. Carbon nanotubes are also of great interest because of several unsurpassable physical properties and it needs to be shown that they are physically stable and structurally unaltered when subjected to irradiation. Therefore, a family of novel nanocarbons (nanodiamond and nanotubes) films deposited by microwave plasma-assisted chemical vapor deposition (MWCVD) technique was subjected to gamma radiation (1, 5, and 20 Mrads) and to medium energy electron-beam irradiation to study their effects on the microscopic structure and corresponding physical properties to establish property-structure correlation. Microstructural and physical properties characterizations prior to and post-irradiation include scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy (RS), X-ray diffraction (XRD), field emission (FE), and high-resolution transmission electron microscopy (HRTEM). Dramatic improvement in the field emission properties for microcrystalline diamond and relatively small but systematic behavior for nanocrystalline diamond with increasing radiation dose is discussed in terms of the critical role of defects which tends to form clusters. The results also indicate that nanocrystalline carbon tends to reach a state of damage saturation they are discussed in terms of sp3, sp2+δ ←→ sp2 C inter-conversion. The effects of electron beam irradiation on the carbon nanotube show that multi¡Vwalled nanotubes tend to be relatively more robust than those of single–walled. This is because increased exposure on an individual bundle of single-walled nanotubes promoted graphitization, pinching, and cross-linking similar to polymers forming intra-molecular junction (IMJ) within the area of electron beam focus, possibly through aggregates of amorphous carbon. Formation of novel nanostructures (nano– ring and helix– V like) due to irradiation is also observed. These studies gleam on the dynamics of nano-manufacturing and a regime of possible relevance to these materials for a) short-term space missions; b) radiation hard programmable logic circuits; and c) radiation pressure sensors.
Lift -Off Process to get Free-Standing High Quality Single Crystal Diamond Films and Suspended Single Crystal Diamond Devices
Authors: Yang Jie , Wang C. F. , Hu E. L. , Butler James E. 
Published: April 2011

ABSTRACTFreestanding and suspended single crystal diamond devices, micro disks and beam structures, have been fabricated on single crystal diamond substrates using a lift-off process employing ion implantation followed by electrochemical etching. The ion implantation created subsurface damage in the diamond while the top surface was sufficiently undamaged that a subsequent homo-epitaxial diamond layer could be grown by chemical vapor deposition (CVD). After the CVD growth and patterning by lithography and reactive ion etching, the underlying damage layer was etched/removed by an electrochemical etch. Different implant ions and energies were simulated and tested to optimize the process. The electrochemical etching process was monitored by an optical video technique. The electrochemical etching process used both ac and dc applied electrical potentials. Photoluminescence (PL), Raman spectra, and polarized light transmission microscopy have been used to characterize the implanted substrate and lift-off films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, CVD growth and the lift-off process. This research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters are discussed in this work. PL spectroscopy indicated differences between the uppermost layers of the homo-epitaxial film and the lift-off interface. Three principal classes of defects have been observed: growth defects inherent in the diamond substrates (type Ib, HPHT), defects induced by the polishing process and associated stress, and point defects.
Development of Thin Film and Nanorod ZnO-Based LEDs and Sensors
Authors: Pearton Stephen J. , Tien L C , Kim H S , Norton D P , Chen J J , Wang H T , Kang B S , Ren F , Lim W T , Wright J , Khanna R , Voss L F , Stafford L , Jun J , Lin Jenshan 
Published: April 2011

ABSTRACTThe development of new etching and contact metallurgies for the ZnO/ZnMgO/ZnCdO materials system and various approaches for realizing ZnO LEDs are reviewed. ZnO nanorod MOSFETs and pH sensors have been demonstrated. In addition, selective detection of hydrogen with Pt-coated single ZnO nanorods is discussed discussed. The Pt-coated single nanorods show a current response approximately a factor of three larger at room temperature upon exposure to 500ppm H2 in N2 than thin films of ZnO. The power consumption of these sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The ZnO nanorods are insensitive to oxygen in the measurement ambient.
Electrical and Magnetic Properties of Doped ZnO Nanowires
Authors: Panin Gennady N , Baranov Andrey N. , Kang Tae Won , Kononenko Oleg V. , Dubonos Sergey V. , Min S. K. , Kim H. J. 
Published: April 2011

ABSTRACTZnO nanowires doped with Mn, Fe, Sn, and Li during the thermal growth following direct chemical synthesis were investigated using electric and magnetic measurements. Current-voltage characteristics of individual nanowires configured as a two-terminal device with Al electrodes show apparent rectify behavior indicating the Schottky-like barrier formation and resistivity being less 3 Ω·cm. Reproducible resistance modulation by a dc voltage at room temperature is observed. Magnetic susceptibility of the doped nanowires as a function of temperature demonstrates Curie–Weiss behavior. Magnetization versus field curves show hysteresis with the coercive field of about 200 Oe. The spatially-resolved magnetic force measurements of individual nanowires revealed the magnetic domain structure. The domains align perpendicular to c-axis and can be polarized in the external magnetic field.
The Growth of ZnO on CrN Buffer Layer Using Surface Phase Control by Plasma Assisted Molecular-beam Epitaxy
Authors: Park Jinsub , Minegishi Tsutomu , Park Seunghwan , Im Inho , Hanada Takahasi , Hong Soonku , Goto Takenari , Cho Meoungwhan , Yao Takafumi 
Published: April 2011

ABSTRACTEpitaxial ZnO films are successfully grown on Al2O3 substrates with phase controlled CrN buffer layer using Zn and O-plasma pre-exposures on CrN layers by plasma assisted molecular beam epitaxy (P-MBE). The Zn exposures on CrN layers prior to ZnO film growth result in the formation of rocksalt CrN without surface oxidation. On the other hand, the surface of the initially deposited CrN layers with rocksalt structure changes into hexagonal structured Cr2O3 after O-plasma exposure as confirmed by reflection high-energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HR TEM). Etching studies show that the ZnO films grown on CrN have +C polarity, while the polarity of ZnO on Cr2O3/CrN double buffer is -C polarity. The interdiffusion of Zn and Cr occurs at the ZnO/CrN interface, while the interdiffusion is negligible at the ZnO/ Cr2O3 interface. The interdiffusion of Cr and Zn can be suppressed by inserting a low-temperature ZnO buffer layer in between ZnO and CrN layers, which helps improve the crystal quality of ZnO layers grown with CrN buffer.
Structural and Optical Studies of Multi Shape ZnO Nanostructures Grown by Direct Vapor Phase Technique
Authors: Hullavarad Shiva S , Karulkar P C , Vispute R D , Heng R , Venkatesan T 
Published: April 2011

ABSTRACTIn this paper we report the growth of ZnO nanowires (12-60 nm) and nanorods (500 nm) by a method of Catalysis Free Direct Vapor Phase (DVP) technique. The nanowires were grown on c-Al2O3 and pulsed laser deposited ZnO nucleation layer on Al2O3 substrates at 800 °C without employing any metal catalysts that are conventionally used in MOCVD or Vapor-Liquid-Solid phase techniques. The ZnO nanowires are found to emit UV light at 386 nm with considerably lower green band emission.
Controllable Synthesis of ZnO Nanonails by Vapor-Solid Process: Growth Mechanism and Structural and Optical Properties
Authors: Umar Ahmad , Haq Q. Ahsanul , Kim Sang Hoon , Im Yeon Ho , Hahn Yoon Bong 
Published: April 2011

ABSTRACTSingle-crystalline with good optical properties aligned ZnO nanonails were grown on steel alloy substrate without the use of metal catalyst or additives by the thermal evaporation process using high purity metallic zinc powder and oxygen as source materials for zinc and oxygen, respectively. Detailed morphological studies by FESEM revealed that the obtained nanonails are grown in a high density over the whole substrate surface and are exhibiting perfect hexagonal-shaped caps. The diameters of the nanonails at their tops and bases are ranges from 120∼160nm and 50∼70 nm, respectively. The detailed structural characterizations confirmed that the synthesized nanostructures are single-crystalline and grown along the c-axis direction. Raman scattering and room-temperature photoluminescence studies demonstrated the wurtzite hexagonal phase and good optical properties, respectively for the grown nanonails.
A Comparative Study of MOCVD Produced ZnO Films Doped with N, As, P and Sb
Authors: Tompa Gary S. , Sun S. , Rice C. E. , Provost L. G. , Mentel D. 
Published: April 2011

ABSTRACTZnO thin films are of interest for an array of applications; including: light emitters, photovoltaics, sensors and transparent contacts among others. Of particular interest is the potential to produce p-type layers from which p-n junction devices could be routinely produced. While it is fairly routine for MOCVD to produce n-type films with doping concentrations in the 10E20 cm-3 range and resistivities below 10E-3 ohm-cm; it is very difficult to produce measurable p-type ZnO. We report on our efforts with doping films p-type using N gas sources and metalorganic sources of P, As, and Sb. Films showing acceptor bands by photoluminescence have been demonstrated; however reliable electrical measurements remain difficult. Specific problems include achieving low resistance ohmic contacts, accounting for the photo-responsiveness of ZnO films and sensitivity limits in Hall measurements of low-doped and compensated materials. The presentation will review deposition parameters, produced and processed films and material characteristics.
Properties of p-Type ZnO Grown by Oxidation of Zn-Group-V Compounds
Authors: Kaminska Eliana , Przezdziecka Ewa , Piotrowska Anna , Kossut Jacek , Boguslawski Piotr , Pasternak Iwona , Jakiela Rafal , Dynowska Elzbieta 
Published: April 2011

ABSTRACTZnO:N and ZnO:Sb layers were obtained by thermal oxidation of Zn compounds with group-V elements. The films are polycrystalline, with the acceptor concentration in the range 1020 cm-3, and the background concentration of H of 5×1019 cm-3. Transport measurements reveal the p-type conductivity with the hole concentrations exceeding 1017 cm-3. Rich photoluminescence spectra involve excitons bound to neutral acceptors and donor-to-acceptor transitions. p-ZnO:N and p-ZnO:Sb films show transparency of about 85 % in the visible wavelength range, making these materials very promising for transparent electronics.
Analysis and Applications of ZnO Semiconductor Films Deposited by Laser and Sputtering Techniques
Authors: Yen Tingfang , Li Meiya , Chokshi Nehal , Kim Sung Jin , Cartwright Alexander N. , Jeong Yongwoo , Anderson Wayne A. 
Published: April 2011

ABSTRACTIn this paper, ZnO thin films deposited by two methods have been studied. Specifically, the films were grown using i) Laser Assisted Molecular Beam Deposition (LAMBD) and ii) RF sputtering. Subsequent to film deposition, a subset of samples deposited using LAMBD were laser annealed. An additional set of samples (from LAMBD and RF sputtering) were annealed with N2 or forming gas at 600°C for 30mins.After deposition, optical and electrical properties of ZnO thin films have been studied. The application of ZnO to optical devices, including Metal-Semiconductor-Metal Photodetectors (MSM-PD) and solar cells, has been made. Several deposition experiments recently demonstrated that the thin films of RF-ZnO and LAMBD-ZnO have near ZnO parameters including refractive index close to 2, 1:1 stoichiometry ZnO, and 3.3 eV ZnO bandgap. Mixtures of single crystal and polycrystal grains were observed by Transmission Electron Microscopy (TEM) from LAMBD ZnO thin films. MSM current-voltage data show symmetrical photo current behavior. High ratio of photocurrent to dark current, good responsivity and fast pulse response of LAMBD-ZnO MSM were observed. ZnO/Si heterojunction solar cell result has been demonstrated and improvement in the ultraviolet light spectrum of spectral response has been shown in this paper.
Optical Properties of Porous ZnO Nanorods Grown by Aqueous Solution Method
Authors: Lee Sang Hyun , Lee Hyun Jung , Goto Takenari , Cho Meoung-Whan , Yao Takafumi 
Published: April 2011

ABSTRACTZnO nanorods were synthesized by chemical solution method at low temperature. The surface of nanorods was changed to porous by using thermal annealing and chemical etching. Surface morphology and their optical properties were changed according to annealing and etching condition. Photoluminescence from as-grown ZnO nanorods almost showed defect related emission in wide range from 450∼900 nm. After annealing at 500°C, the band-edge emission of ZnO was observed and emission at visible range was changed to green with decreasing red-orange. The surface morphology of ZnO nanorods was transformed to porous by chemical etching and it led to increase the intensity of band-edge emission about three times. The internal quantum efficiency for porous ZnO nanorods, which was calculated from ratio PL intensity at 10K and 300K, is about 21%. Also, the random lasing at porous ZnO nanorods was occurred at high optical excitation by a photon with traveling inside or outside of porous ZnO nanorod gets amplified by injection second photon before leaving porous ZnO nanorods.
Synthesis and Characterization of Nickel-Doped ZnO Nanocrystals
Authors: Zhang Xiao Li , Qiao Ru , Li Yan , Qiu Ri , Kang Young Soo 
Published: April 2011

ABSTRACTThe structure and magnetism of ZnO-based solid solutions, dilute magnetic semiconductors, with nickel solute were obtained via a solvothermal method. Compared with previous methods for solid solution DMSs, our synthesis method was really facile and economical. The one-dimensional solid solution of Zn1-xNixO nanostructures were grown in a alcoholic solution. Moreover, the percentage of doped nickel can be easily controlled. The X-ray diffraction, transmission electron micrograph and magnetization hysteresis loops of nickel-doped ZnO nanocrystals were presented to confirm that the nickel impurities are embedded inside the nanocrystal.
Transport Studies of Transition Metal Ion Doped ZnO: Bulk and Thin Films
Authors: Singh Shubra , Rama N , Ramachandra Rao M.S. 
Published: April 2011

ABSTRACTThe effect of doping of transition metal ions (Fe and Co) on transport properties of ZnO has been studied in both bulk and thin films. The solubility limit of these ions have been found to be higher in thin films compared to bulk. Optical measurements reveal the presence of Fe in both 2+ and 3+ state. Co is believed to be in 2+ states. Electrical resistivity measurements show that while for bulk Fe doped ZnO samples there is a decrease in resistivity compared to undoped ZnO, it increases for bulk Co doped ZnO samples. However, thin film samples of both types of doped compounds show a decrease in resistivity compared to undoped ZnO. This difference in bulk and thin film behaviour has been explained on the basis of experimental results.