ICMCTF2007 Session D1: Boron Nitride, Carbon Nitride and Group-III Nitride Materials

Wednesday, April 25, 2007 8:00 AM in Room Sunset

Wednesday Morning

Start	Invited?	Item
8:00 AM	Invited	D1-1 Deposition of Thick Cubic Boron Nitride Films - Mechanisms and Concepts W. Kulisch (Joint Research Center, Italy) The state of the art of the deposition of thick, well-adherent cubic boron nitride films is reviewed. Despite the outstanding properties of c-BN, and although considerable progress has been achieved in the last 15 years, development of a c-BN technology is still hampered by the lack of deposition processes allowing to deposit routinely and easily thick films on any desired substrate. Rather, in most cases adhesion failure is observed when a certain thickness (some hundred nm) is exceeded. When analyzing the underlying reasons it is important to take into account the peculiarities of c-BN deposition: the unique nucleation sequence and the narrow process window which is in addition different for nucleation and growth. It will be shown that two reasons are responsible for the poor adhesion: The high compressive stress caused by the strong ion bombardment, and the low adhesion strength on almost all substrates. As the former is affected by the growth process, the latter by the nucleation step, it is possible to treat them independently. A model is presented which describes the formation and relaxation of stress by the ion bombardment, and several measures to reduce the stress proposed in the literature (high temperature deposition, post-deposition annealing, high energy ion bombardment, addition of foreign elements etc.) are critically discussed. In order to improve the adhesion strength, best results have been obtained with a variety of (in most cases graded) interlayers, which will be compared briefly. Finally, on the basis of this discussion and experimental results, a concept for the deposition of thick, well-adherent cubic boron nitride films is presented.
8:40 AM		D1-3 Investigation of Wurtizitic (B,Al)N Films Prepared on Polycrystalline Diamond J.H. Song, J.-L. Huang (National Cheng-Kung University, Taiwan); H.-H. Lu (National Chin-Yi Institute of Technology, Taiwan); J.C. Sung (Kinik Company, Taiwan) Using highly c-axis orientated AlN as a buffer layer to grow epitaxial GaN on polycrystalline diamond is an attractive application for heat dissipation of LED devices. In this study, the (B,Al)N layer was used to bridge the gap of lattice mismatch between diamond and AlN. For the preparation of (B,Al)N films on diamond substrate, aluminum target was sputtered in DC mode and hBN in RF mode simultaneously in a pure nitrogen plasma. The results showed boron content in (B,Al)N film which were determined by photoelectron spectroscopy (XPS) increased with RF sputtering power increasing. And lattice constant of (B,Al)N films were smaller than pure AlN, suggesting the substitution of smaller boron atoms at Al positions. As the boron content increased, the crystallite of (B,Al)N films decreased. The crystal qualities of AlN films was analyzed by rocking curve, and AlN was deposited on low boron content (B,Al)N layer with higher c-axis preferential orientation than it was grown on diamond directly.
9:00 AM		D1-4 Preparation of Carbon Nitride using Microwave Plasma CVD Y. Sakamoto (Chiba Institute of Technology, Japan) The research on Carbon-Nitrogen group materials such as Carbon Nitride and CN_x has been investigated. Especially, C₃N₄ has the possibility of the hardness exceed the diamond, especially. For the purpose of growth of Carbon Nitride, this report examined on the effect of the growth condition for the preparation of the Carbon Nitride using microwave plasma CVD from CH₄-N₂ reaction gas system. The microwave plasma CVD apparatus was used for synthesis of the Carbon Nitride. CH₄-N₂ system was used for the reaction gas system, and CH₄/N₂ concentration was changed from 1 to 10%. The estimation of the deposits carried out by SEM, AES, ESCA, XRD, and Raman spectroscopy. From the SEM image of the deposit synthesized at CH₄ concentration; 1%, the size of the each rods are 2µm in diameter and 5µmm length. From the observation in higher magnification, crystal habit like hexagonal was observed. On the other hand, the SEM image of the deposit at CH₄ concentration; 7% shows the surface covered with the whiskers of about 1m in diameter. Si, C, N and O peaks were observed in AES spectra of all samples. Composition of the deposit at CH₄ concentration; 1% calculated from the AES spectrum, nitrogen concentration was 57.5%. In XRD pattern of the deposit at lower CH₄ concentration, the peaks of -C₃N₄ (301), (401) planes were recognized. On the chemical bonding, C-N and C=N bonding were obtained in XPS spectra. The surface morphologies of the deposits were changed from crystals to whiskers with increasing of CH₄ concentration. Crystalline -C₃N₄ was obtained at lower CH₄ concentration using microwave plasma CVD from CH₄-N₂ reaction gas system.
9:20 AM		D1-5 The Effect of Nitrogen Atoms Included in CN_x Coating on Friction Sliding Against Si₃N₄ Ball in Nitrogen Gas T. Tokoroyama (Nagoya University, Japan); M. Goto (Ube National College of Technology, Japan); F. Honda (Toyota Technological Institute, Japan); N. Umehara (Nagoya University, Japan) Carbon nitride (CN_x) coating is one of the expected materials for well tribological properties as low friction and high wear resistance. This material showed friction coefficient lower than 0.01 if it slid against a Si₃N₄ ball in N₂. The mechanism of this superlow friction phenomena was considered that the CNx sliding surface changed to a low-shear-strength layer by forming a graphite-like structure. However, effects of both nitrogen atoms in the coating and from ambient N₂ gas on the transformation of surface layers of CNx remain unclear. Thus, in this work, we investigated the relationship between the friction coefficient and nitrogen concentration in the wear track on the CNx coating. We measured the intensity of C KLL and N KLL on the wear track of CNx by Auger electron spectroscopy (AES). We compared between the N KLL/C KLL ratios of wear tracks which slid in N₂ and in air. In the case of wear track slid in N₂, the ratio drastically decreased with sliding cycles and reached to almost zero. During process, friction coefficient decreased with the sliding cycles and reached to about 0.01. On the other hand, the ration and friction coefficient did not drastically decreased with sliding cycles in the air. It can be considered from these results that the exodiffusion of N atom had taken from CN_x surface in N₂ so much, and friction coefficient decreased with N KLL/C KLL ratio.
9:40 AM		D1-6 Plasma Processing in Carbon Containing Atmosphere for Possible Treatment of Wind Turbine Components M. Zlatanovic (Faculty of Electrical Engineering, Serbia); N. Popovic (Nuclear Science Institute Vin, Belgrade, Serbia) We propose a new pulse plasma surface treatment consisting of plasma nitriding and subsequent plasma post nitrocarburizing, which improves the fatigue resistance, wear resistance and corrosion resistance and contributes to the lowering of weighted acoustic level. This process is a candidate for surface treatment of wind turbine gears which are exposed to severe working conditions including high mechanical stresses, alternative load, surface wear and corrosion and during the operation they can be source of high sound level witch influences the environment. The samples made of steel grades AISI C 1045, 4140 and H 11 were pulse plasma nitrided and plasma post-nitrocarburized. The Vickersâ?Ts method was used for surface microhardness and depth profiling measurements, while the microstructure and surface zone morphology were examined by the optical microscopy and SEM. The surface zone phase analysis was performed by XRD method while the ball-grinding technique was used to measure the compound zone thickness. It was demonstrated that a low friction, chemically stable single-phase magnetite superficial layer can be formed by plasma post-oxidation of various steel grade substrates in the same batch. The post treatment in carbon containing atmosphere resulted in formation of a surface layer with gradually increased carbon content. Raman and IR spectra revealed the presence of an amorphous carbon based layer, while the formation of the cementite phase was found by XRD analyses. The surface layer composition was obtained by GDS analysis. The corrosion test revealed the enhanced corrosion resistance of postoxidized samples, while the running engine test with pulse plasma treated timing gears demonstrated the decrease of noise emission.
10:00 AM	Invited	D1-7 1D III-Nitride Nanomaterials - Superb Photoconductivity and Luminescence K.H. Chen, R.S. Chen (Academia Sinica, Taiwan); H.Y. Chen, L.C. Chen (National Taiwan University, Taiwan); S. Chattopadhyay (National Chung Hsing University, Taiwan) An overview of our recent works on one-dimensional nanostructures, with special emphasis on group III nitrides nanowires¹, nanobelts² and nanotips³ will be presented. All these 1D nanostructures exhibit interesting optical and electrical properties unmatched by their thin film or bulk counterparts. For instance, the InN nanobelts exhibit sharpest PL peak in the IR region reported to date for the InN system, and their power-dependent PL data also suggest lasing behavior. A "step edge" model has been proposed to explain the growth of solid nanotips of AlN and InN. The model predicts a set of apex angles for AlN and InN nanotips, which is in good agreement with the apex angles measured in InN nanotips⁴. Photoconductivity (PC) studies on arrayed GaN nanowires reveal responsivity and gain several orders of magnitude higher than those reported for thin films. A spatially separated electronic transport mechanism is proposed to explain the ultra-long carrier lifetime (>10^-3 s) observed in nanowires. A scheme that allows on-chip growth of an ensemble of nanowires for device application is also demonstrated. In addition, nanoscale engineering and strategies for either dispersing noble-metal nanoparticles on the nanotip arrays or encapsulating them inside dielectric nanowires, in a self-assembled manner, will be presented. ¹C.-C. Chen et al., J. Am. Chem. Soc. 123, 2791-2798 (2001). ²M. S. Hu et al., Adv. Func. Mater. 16, 537 (2006). ³C.H. Hsu et al., Nano Letters 4, 471 (2004).⁴ S. Chattopadhyay et al., An invited review article for Critical Reviews in Solid state and Material Science 31, 15-53 (2006).
10:40 AM	Invited	D1-9 Structural and Electrical Characterization of Laser Debonded AlGaN/GaN HEMTs C. Surya, K.K. Leung, C.P. Chan, M. Pilkuhn, K.H. Pang (The Hong Kong Polytechnic University, Hong Kong) In this paper we present detailed investigations of high-quality free-standing AlGaN/GaN HEMTs which are separated from the sapphire substrate by laser lift-off. Structural and stress-strain analyses of the HEMTs are performed by high-resolution x-ray diffraction (HXRD) and transmission electron microscopy (TEM) measurements. The computational simulation agrees well with the experimental results indicating that no edge threading dislocation is introduced in the heterojunctions during laser lift-off. This corroborates with the studies on the I-V characteristics of the devices, which also indicates no degradation in the electronic properties after laser debonding.
11:20 AM		D1-11 Double-Crystal X-Ray Topography of Free-Standing HVPE Grown n-Type GaN and High Resolution PL Studies N.A. Mahadik (George Mason University); S.B. Qadri (US Naval Research Laboratory); M. Murthy, M.V. Rao (George Mason University); J.A. Freitas (US Naval Research Laboratory); J. Kim (Korea University, Korea) GaN is a well known material for its potential electronic and optoelectronic applications. However, GaN could have structural defects arising due to mismatch in lattice parameters and thermal expansion coefficients between the GaN epilayer and its substrates. In order to reduce the number of defects, freestanding GaN samples have very recently been fabricated. The GaN samples are grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates and then removed from the substrate by laser lift-off process. These samples are expected to have better crystalline quality and lesser defects due to the strain relaxation in the freestanding GaN films. To determine the crystalline quality, strain distribution, and surface defect structure, high resolution x-ray topographs and rocking curves were obtained on free standing HVPE grown n-type GaN. Intrinsic rocking curves were measured for the (00l) reflections using a triple axis four-circle diffractometer. The full width at half maximum (FWHM) ranged between 60 and 88 arcseconds, indicating good crystalline quality. High resolution x-ray topographs were obtained using double crystal geometry in which asymmetrically cut Si (111) was used to monochromatize and expand the incident x-ray beam. The topographic images revealed areas of high dislocation density, ridges, and inclusions. In addition, hexagonal cavities are also observed. Since the films were warped, the radius of curvature was measured and found it be of the order of 1 m. Photoluminescence (PL) and Cathodoluminescence (CL) were applied to determine the nature of extended defects in these freestanding films. FWHM of the PL spectra was used as a figure of merit for the quality of the films and was found to be consistent with the FWHM measured by HRXRD. Also, presence of the hexagonal cavities was confirmed by the CL measurements.
11:40 AM		D1-12 GaN Nanowires - Influence of the Starting Material on Nanowire Growth K.H. Tam, A.B. Djurisic, Y.F. Hsu (University of Hong Kong) GaN is a wide band gap (3.4 eV) semiconductor, which is of great interest for various applications, such as short wavelength optoelectronic device applications, as well as high power/high temperature electronic applications. In recent years, there has been increasing interest in the fabrication and characterization of GaN nanostructures. In this work, GaN nanowires were fabricated on Si substrates coated with Au or Ni catalyst with a thermally-assisted chemical vapor deposition method by evaporating mixture of Ga(0.04g), GaN(0.04g), MnO₂ and carbon (single wall carbon nanotubes (SWCNT) or graphite) at 1100°C in ammonia gas flow. The fabricated nanostructures were characterized by scanning electron microscopy using LEO 1530 FESEM, energy dispersive X-ray spectroscopy, and X-ray diffractometry. We investigated the influence of the source of carbon and substrate temperature on the morphology and composition of the nanowires. We found that the nanowire composition is strongly affected by the substrate temperature, with oxygen incorporation increasing with decreasing substrate temperature. All nanowires exhibited very low Mn content, and nanowire composition and morphology were also dependent on whether graphite or carbon nanotubes were used as a source material. Growth mechanism and properties of obtained nanostructures are discussed.