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Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Description: Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Date: May 1, 1996
Creator: Kiggans, J.O.: Tiegs, T.N. & Kimrey, H.D.
Partner: UNT Libraries Government Documents Department

Scale-up of microwave nitridation of sintered reaction bonded silicon nitride parts. Final report

Description: Scale-up were performed in which microwave heating was used to fabricate reaction-bonded silicon nitride and sintered reaction-bonded silicon nitride (SRBSN). Tests were performed in both a 2.45 GHz, 500 liter and a 2.45 GHz, 4000 liter multimode cavities. The silicon preforms processed in the studies were clevis pins for diesel engines. Up to 230 samples were processed in a single microwave furnace run. Data were collected which included weight gains for nitridation and sintering studies were performed using a conventional resistance-heated furnace.
Date: October 1, 1997
Creator: Tiegs, T.N.; Kiggans, J.O. & Garvey, G.A.
Partner: UNT Libraries Government Documents Department

Properties and challenges of nanolayer coatings

Description: A systematic study was made on MoSi{sub 2}-based nanolayer coatings. Alternating layers with thickness 1-20 nm were prepared by sputtering. Nitrided MoSi{sub 2} has a very high crystallization temperature, >1000 C, and MoSi{sub 2}Nx (x=3-4) can be used as a stable second phase reinforcement or diffusion barrier coatings. Mechanical properties depend strongly on phase and morphology of the layers: hardness and modulus is significantly increased in the crystallization. The nanolayers have much higher hardness but lower modulus (which project higher toughness in the nanolayers). Wear resistance is improved with decreasing layer thickness. Single phase MoSi{sub 2}Nx (x=0-4.2) has a wide range of hardness and modulus with varying N content and annealing, suggesting the possibility of engineering MoSi{sub 2}Nx to produce different material properties for different mechanical applications. Most of this paper is made up of viewographs.
Date: December 1995
Creator: Kung, H.; Nastasi, M.; Jervis, T.; Mitchell, T. & Hirvonen, J. P.
Partner: UNT Libraries Government Documents Department

Gelcasting of silicon compositions for SRBSN

Description: Compositions of high purity silicon metal containing various oxides as sintering aids were gelcast to prepare green bodies for subsequent nitridation and sintering to form sintered reaction bonded silicon nitride (SRBSN). An acidic aqueous and an alcohol-based gelcasting system were used. The solids content in the slurry affected the green density of the cast samples, however, there was no apparent correlation between the green density and the percent nitridation. Samples were nitrided under flowing, high-purity nitrogen in either a tungsten element furnace, a graphite element furnace, or in a microwave furnace. The samples nitrided in the graphite and microwave furnaces showed 9--16% higher levels of nitridation than in the tungsten furnace. A N{sub 2}-4% H{sup 2} gas mixture was compared to pure nitrogen in the tungsten furnace. The addition of the hydrogen increased nitridation levels by 14--19%. The nitrided and sintered SRBSN ceramics had densities of 95--98% of theoretical, with no direct relationship being observed between the level of nitridation and the fired density. The average 4-point flexure strength of the samples ranged from 428 to 741 MPa.
Date: December 31, 1995
Creator: Nunn, S.D.; Kiggans, J.O. Jr.; Simpson, R.E. II & Maria, J.P.
Partner: UNT Libraries Government Documents Department

Identification of nitriding mechanisms in high purity reaction bonded silicon nitride

Description: The rapid, low-temperature nitriding results from surface effects on the Si particles beginning with loss of chemisorbed H and sequential formation of thin amorphous Si nitride layers. Rapid complete conversion to Si{sub 3}N{sub 4} during the fast reaction can be inhibited when either too few or too many nuclei form on Si particels. Optimally, {approximately} 10 Si{sub 3}N{sub 4} nuclei form per Si particles under rapid, complete nitridation conditions. Nitridation during the slow reaction period appears to progress by both continued reaction of nonpreferred Si{sub 3}N{sub 4} growth interfaces and direct nitridation of the remaining Si/vapor interfaces.
Date: March 1, 1993
Creator: Haggerty, J. S.
Partner: UNT Libraries Government Documents Department

Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)

Description: Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.
Date: October 31, 2008
Creator: Oshima, Yasuhiro; /Stanford U., Materials Sci. Dept.; Sun, Yun; /SLAC, SSRL; Kuzum, Duygu; U., /Stanford et al.
Partner: UNT Libraries Government Documents Department

Sintered Reaction Bonded Silicon Parts by Microwave Nitridation Combined with Gas-Pressure Sintering

Description: The cooperative project was a joint development program between Ceradyne and Oak Ridge National Laboratory through Lockheed Martin Energy Research (LMER). Cooperative work was of benefit to both parties. ORNL was able to assess the effect of the microwave nitridation process coupled with gas-pressure sintering for fabrication of parts for advanced diesel engines. Ceradyne gained access to gelcasting expertise and microwave facilities and experience for the nitridation of SRBSN materials. The broad objective of the CRADA between Ceradyne and OIWL was to (1) examine the applicability of the gelcasting technology to fabricate parts from SRBSN, and (2) to assess the effect of the microwave nitridation of silicon process coupled with gas-pressure sintering for fabrication of parts for advanced diesel engines. The following conclusions can be made from the work performed under the CRADA: (1) Gelcasting is a viable method to fabricate SRBSN parts using Ceradyne Si mixtures. However, the technique requires further development prior to being put into commercial use. (2) Microwave heating can be utilized to nitride multiple SRBSN parts. Scale-up of the process to fabricate several kilograms of material (up to 6 kg) per furnace run was demonstrated.
Date: January 1, 1999
Creator: Kiggans, J.O.; Mikijelj, B. & Tiegs, T.N.
Partner: UNT Libraries Government Documents Department

Improvements in bis(cyclopentadienyl)magnesium purity as determined with gas chromatography-mass spectroscopy

Description: Bis(cyclopentadienyl)magnesium (MgCp2) is used commonly as a source for doping nitride materials with magnesium. Increased oxygen incorporation known to accompany the use of MgCp2 makes the purity of this precursor an important consideration in nitride CVD. Gas chromatography-mass spectroscopy (GCMS) methods have now been developed for the identification of volatile impurities in MgCp2. Diethylether, an oxygen containing organic compound (CH{sub 3}CH{sub 2}OCH{sub 2}CH{sub 3}), and additional organic impurities were found in the MgCp2 supplied by three manufacturers. Subsequent refinements in the synthetic processes by these companies have resulted in the availability of MgCp2 free of ether and other organic impurities as determined by GCMS.
Date: March 8, 2000
Partner: UNT Libraries Government Documents Department

Enhanced thermal capacity aerogels summary report for FY 1993

Description: In a continuation of work done previously, the authors have fabricated a set of silica aerogels and then chemically modified their internal surfaces for the purpose of inhibiting the effects of sintering at high temperatures. They performed surface nitridation of silica aerogels, i.e., the replacement of surface oxygen atoms with nitrogen atoms, by reacting ammonia gas with the silica surfaces at elevated temperatures. After pre-oxidizing the aerogels, they exposed three sets of samples to anhydrous ammonia gas under different processing conditions. Each set contained silica aerogels of three different densities, 0.07 g/cc, 0.16 g/cc, and 0.29 g/cc. The treated samples, together with companion untreated reference samples, were sent to NASA Ames Research Laboratory for high temperature testing. They also fabricated two carbon aerogel cylinders, 7 cm diameter x 1.5 cm thick. These samples were also delivered to NASA Ames Research Laboratory for high temperature tests.
Date: December 1, 1993
Creator: Hrubesh, L.W.; Coronado, P.R. & Poco, J.F.
Partner: UNT Libraries Government Documents Department

Continuous spray forming of functionally gradient materials

Description: Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component functional gradient material of copper, tungsten, boron, and boron nitride. The FGM was formed with continuous gradients and integral cooling channels eliminating bondlines and providing direct heat transfer from the high temperature exposed surface to a cooling medium. Metallurgical and x-ray diffraction analyses of the materials formed through innovative VPS (vacuum plasma spray) processing are also presented. Applications for this functional gradient structural material range from fusion reactor plasma facing components to missile nose cones to boilers.
Date: December 1, 1995
Creator: McKechnie, T.N. & Richardson, E.H.
Partner: UNT Libraries Government Documents Department

A study of nitrogenation of a NdFe{sub 12-x}Mo{sub x} compound by in situ neutron powder diffraction.

Description: The effects on the crystal lattice of a NdFe{sub 12{minus}x}Mo{sub x}(x {approx_equal} 1.7) compound which contained {approximately}12 vol% of bcc-Fe were studied by neutron powder diffraction during controlled nitrogenation over the 25-600 C temperature range. The sample inside the furnace was connected to a closed volume of ultra-pure nitrogen gas while neutron data were collected over regular time intervals during sequential heating. Substantial nitrogen absorption occurred between 500 to 600 C. During the nitrogenation process the NdFe{sub 12{minus}x}Mo{sub x}N{sub y} lattice expanded while the bcc-Fe lattice contracted. An increasing decomposition of the compound into bcc-Fe at 600 C was observed. The average size of the NdFe{sub 12{minus}x}Mo{sub x}N{sub y} crystalline grains decreased starting at {approximately}300 C, reaching a minimum at {approximately}500 C and then increased markedly at higher temperatures. The development of lattice strains, on the other hand, showed an opposite trend, i.e., a maximum at 500 C. A correlation of structural modification of the crystalline phases and the nitrogenation process is discussed.
Date: November 18, 1997
Creator: Ding, Y.; Lin, J.; Loong, C.-K. & Short, S. M.
Partner: UNT Libraries Government Documents Department

Molecular beam epitaxy of InN dots on nitrided sapphire

Description: A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.
Date: April 20, 2007
Creator: Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV. & Leone, Stephen R.
Partner: UNT Libraries Government Documents Department

Compatibility/Stability Issues in the Use of Nitride Kernels in LWR TRISO Fuel

Description: The stability of the SiC layer in the presence of free nitrogen will be dependent upon the operating temperatures and resulting nitrogen pressures whether it is at High Temperature Gas-Cooled Reactor (HTGR) temperatures of 1000-1400 C (coolant design dependent) or LWR temperatures that range from 500-700 C. Although nitrogen released in fissioning will form fission product nitrides, there will remain an overpressure of nitrogen of some magnitude. The nitrogen can be speculated to transport through the inner pyrolytic carbon layer and contact the SiC layer. The SiC layer may be envisioned to fail due to resulting nitridation at the elevated temperatures. However, it is believed that these issues are particularly avoided in the LWR application. Lower temperatures will result in significantly lower nitrogen pressures. Lower temperatures will also substantially reduce nitrogen diffusion rates through the layers and nitriding kinetics. Kinetics calculations were performed using an expression for nitriding silicon. In order to further address these concerns, experiments were run with surrogate fuel particles under simulated operating conditions to determine the resulting phase formation at 700 and 1400 C.
Date: February 1, 2012
Creator: Armstrong, Beth L & Besmann, Theodore M
Partner: UNT Libraries Government Documents Department

Improved heteroepitaxial MBE GaN growth with a Ga metal buffer layer

Description: We demonstrate that the use of pure gallium (Ga) as a buffer layer results in improved crystal quality of GaN epilayers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire. The resulting epilayers show electron Hall mobilities as high as 400 cm 2 /Vs at a background carrier concentration of 4 x 10 17 cm -3 , an outstanding value for an MBE-grown GaN layer on sapphire. Structural properties are also improved; the asymmetric (101) X-ray rocking curve width is drastically reduced with respect to that of the reference GaN epilayer grown on a low-temperature GaN buffer layer. Nitrided Ga metal layers were investigated for different Ga deposition time. These layers can be regarded as templates for the subsequent Ga main layer growth. It was found that there is an optimum Ga metal layer deposition time for improving the electron mobility in the epilayer. Heating of the Ga metal layer to the epilayer growth temperature under nitrogen plasma is found to be sufficient to produce highly oriented GaN crystals. However, nonuniform surface morphology and incomplete surface coverage were observed after nitridation of comparatively thick Ga metal layers. This is shown to be the reason for the decreasing electron mobility of the epilayers as the Ga metal layer thickness exceeds the optimum value.
Date: May 15, 2000
Creator: Kim, Yihwan; Subramanya, Sudhir G.; Krueger, Joachim; Siegle, Henrik; Shapiro, Noad; Armitage, Robert et al.
Partner: UNT Libraries Government Documents Department

The use of reactive ion sputtering to produce clean germanium surfaces in a carbon rich environment -- An ion scattering study

Description: The authors have used the ion spectroscopic techniques of direct recoil spectroscopy (DRS) and mass spectroscopy of recoiled ions (MSRI) to demonstrate that low energy reactive ion sputtering of Ge is capable of removing surface impurities such as carbon. The experiments were performed in a vacuum chamber maintained at 3.5 {times} 10{sup {minus}7} Torr. At these pressures, physical sputtering using noble gas is not effective for cleaning Ge surfaces as carbon re-deposits onto the surface. In this paper, the authors demonstrate that reactive sputtering of Ge using 4.0 keV nitrogen at a Ge surface temperature of {approximately} 740 K and above removes surface carbon and deposits nitrogen on the Ge surface. Heating the nitrogen exposed Ge surface to above {approximately} 880 K results in the desorption of nitrogen and generates an atomically clean Ge surface, under poor vacuum conditions.
Date: October 7, 1997
Creator: Smentkowski, V.S.; Krauss, A.R.; Gruen, D.M.; Holecek, J.C. & Schultz, J.A.
Partner: UNT Libraries Government Documents Department

Mechanical properties of, and phase transformation in, V-Cr-Ti-O solid solutions

Description: Incorporation of O in the surface of V-Ti-Cr alloys has been investigated in controlled environments at 550-750{degrees}C. and tests were performed to determine the physical properties of V-Cr-Ti-O solid solutions. The amount of O in the alloys has been determined by weight-change measurements. Microhardness was used to determine O depth profiles in the alloys. X-ray, diffraction indicated a phase transformation from body-centered-cubic (bcc) to tetragonal in the highly stressed lattice because of O incorporation. Cr depletion was observed near alloy grain boundaries, based on back-scattered-electron images and electron-energy-dispersive spectra. Elastic modulus and Vickers hardness also increased in O-enriched V-Cr-Ti alloys. Hardening in the alloys results from O atoms on face-centered interstitial sites in the bcc sublattice and the formation of very fine coherent oxide particles. O or N diffusion occurs via the interstitial sublattice of the bcc V-base alloys and is accompanied by the formation of homogeneous oxide or nitride phases via internal oxidation or nitridation. The O,N-enriched surface region exhibited the extraordinarily high Vickers hardness of -18 GPa (1800 kg/mm{sup 2}). A value typical of oxides, nitrides, or carbides, or obtainable by ion-beam irradiation of metals.
Date: November 1, 1995
Creator: Park, J.H.; Kuppermann, D. & Park, E.T.
Partner: UNT Libraries Government Documents Department

Microstructure and mechanical properties of nitrided molybdenum silicide coatings

Description: Mo-Si-N films with a high nitrogen concentration were produced by sputter-deposition in nitrogen plasma. Chemical composition was determined with Rutherford backscattering and nuclear reaction analysis. Ratio of Mo to Si was 1:2 in the coatings with a nitrogen concentration of 50%. Microstructure of the as-deposited coatings on a silicon substrate was amorphous and no crystallization was found after annealing up to 1000{degree}C, although some relaxation was observed in X-ray diffraction. This was confirmed by high-resolution TEM. Hardness of Mo-Si-N films was 18.8 GPa as determined with a nanoindenter. This is significantly higher than that of MoSi{sub 2} films, 11.2 GPa. Hardness of the Mo-Si-N films increased to 24.4 GPa after annealing at 800{degree}C, which is the same as that of the tetragonal phase of MoSi{sub 2}, 25.5 GPa. Similarly, modulus of as-deposited Mo-Si-N film was higher (257 GPa) than that of MoSi{sub 2} film (222 GPa). However, only a slight increase in the modulus of the Mo-Si-N film was found after annealing at 800C, whereas the modulus of the crystallized tetragonal MoSi{sub 2} was 382 GPa. No cracking was found in the Mo-Si-N films even after annealing at 1000C.
Date: December 31, 1993
Creator: Hirvonen, J. P.; Suni, I.; Kattelus, H.; Lappalainen, R.; Torri, P.; Kung, H. et al.
Partner: UNT Libraries Government Documents Department

Development of silicon nitride composites with continuous fiber reinforcement

Description: The composites were fabricated using ultrafine Si powders prepared by attritor milling; the powders exhibits full conversion to Si nitride in < 3 h at {le} 1200 C (these conditions reduce degradation of the fibers compared to conventional). Effects of processing conditions on fiber properties and the use of fiber coatings to improve stability during processing as well as change the fiber-matrix interfacial properties were investigated. A duplex carbon-silicon carbide coating, deposited by CVD, reduced fiber degradation in processing, and it modified the fiber-matrix adhesion. Si nitride matrix composites were fabricated using reaction sintering, forming laminates, filament-wound plates, and tubes. In each case, an attritor milled Si powder slurry is infiltrated into ceramic fiber preforms or tows, which are then assembled to form a 3-D structure for reaction sintering. The resulting composites have properties comparable to chemical vapor infiltration densified composites, with reasonable strengths and graceful composite fracture behavior.
Date: October 1, 1993
Creator: Starr, T. L.; Mohr, D. L.; Lackey, W. J. & Hanigofsky, J. A.
Partner: UNT Libraries Government Documents Department

H-Diffusion Mechanism(s) in PECVD Nitride Passivation of Si Solar Cells: Preprint

Description: Presented at the 2001 NCPV Program Review Meeting: Modeled diffusion of H in 2-step Si{sub 3}N{sub 4} passivation process invoking concept of storage of H. H stored during nitridation is redistributed during subsequent anneal. The modeling results agree with this hypothesis, and the conclusions also appear to concur with the observations.
Date: October 1, 2001
Creator: Sopori, B. & Zhang, Y.
Partner: UNT Libraries Government Documents Department

Benefits of microscopy with super resolution

Description: Transmission Electron Microscopy developed from an imagingtool into a quantitative electron beam characterization tool that locallyaccesses structure, chemistry, and bonding in materials with sub Angstromresolution. Experiments utilize coherently and incoherently scatteredelectrons. In this contribution, the interface between gallium nitrideand sapphire as well as thin silicon gate oxides are studied tounderstand underlying physical processes and the strength of thedifferent microscopy techniques. An investigation of the GaN/sapphireinterface benefits largely from the application of phase contrastmicroscopy that makes it possible to visualize dislocation corestructures and single columns of oxygen and nitrogen at a closest spacingof 85 pm. In contrast, it is adequate to investigate Si/SiOxNy/poly-Siinterfaces with incoherently scattered electrons and electronspectroscopy because amorphous and poly crystalline materials areinvolved. Here, it is demonstrated that the SiOxNy/poly-Si interface isrougher than the Si/SiOx interface, that desirable nitrogen diffusiongradients can be introduced into the gate oxide, and that a nitridationcoupled with annealing increases its physical width while reducing theequivalent electrical oxide thickness to values approaching 1.2 nm.Therefore, an amorphous SiNxOy gate dielectric seems to be a suitablesubstitute for traditional gate oxides to further increase device speedby reducing dimensions in Si technology.
Date: July 9, 2001
Creator: Kisielowski, C.; Principe, E.; Freitag, B. & Hubert, D.
Partner: UNT Libraries Government Documents Department

Issues associated with the metalorganic chemical vapor deposition of ScGaN and YGaN alloys.

Description: The most energy efficient solid state white light source will likely be a combination of individually efficient red, green, and blue LED. For any multi-color approach to be successful the efficiency of deep green LEDs must be significantly improved. While traditional approaches to improve InGaN materials have yielded incremental success, we proposed a novel approach using group IIIA and IIIB nitride semiconductors to produce efficient green and high wavelength LEDs. To obtain longer wavelength LEDs in the nitrides, we attempted to combine scandium (Sc) and yttrium (Y) with gallium (Ga) to produce ScGaN and YGaN for the quantum well (QW) active regions. Based on linear extrapolation of the proposed bandgaps of ScN (2.15 eV), YN (0.8 eV) and GaN (3.4 eV), we expected that LEDs could be fabricated from the UV (410 nm) to the IR (1600 nm), and therefore cover all visible wavelengths. The growth of these novel alloys potentially provided several advantages over the more traditional InGaN QW regions including: higher growth temperatures more compatible with GaN growth, closer lattice matching to GaN, and reduced phase separation than is commonly observed in InGaN growth. One drawback to using ScGaN and YGaN films as the active regions in LEDs is that little research has been conducted on their growth, specifically, are there metalorganic precursors that are suitable for growth, are the bandgaps direct or indirect, can the materials be grown directly on GaN with a minimal defect formation, as well as other issues related to growth. The major impediment to the growth of ScGaN and YGaN alloys was the low volatility of metalorganic precursors. Despite this impediment some progress was made in incorporation of Sc and Y into GaN which is detailed in this report. Primarily, we were able to incorporate up to 5 x 10{sup 18} cm{sup -3} ...
Date: July 1, 2009
Creator: Koleske, Daniel David; Knapp, James Arthur; Lee, Stephen Roger; Crawford, Mary Hagerott; Creighton, James Randall; Cross, Karen Charlene et al.
Partner: UNT Libraries Government Documents Department

Wafer Preparation and Iodine-Ethanol Passivation Procedure for Reproducible Minority-Carrier Lifetime Measurement (Poster)

Description: Measurement of the bulk minority-carrier lifetime (T{sub b}) by optical methods, such as photocurrent decay or quasi-steady-state photoconductance (QSSPC), is strongly influenced by surface recombination. Several techniques are known to lower the effective surface recombination velocity, including the following: use of oxidation, floating N/P junction, SiN:H layer, HF immersion, and use of iodine in ethanol or methanol (I-E solution). Using I-E appears to be very simple and does not require any high-temperature treatment such as oxidation, diffusion, or nitridation processes, which can change T{sub b}. However, this is not a preferred procedure within the photovoltaic community because it is difficult to obtain same T{sub b} values reproducibly, particularly when the wafer lifetime is long. The objectives are: (1) Investigate various reasons why lifetime measurements may be irreproducible using I-E solution passivation. (2) Study the influence of the strength of iodine in the ethanol solution, wafer-cleaning procedures, influence of the wafer container during lifetime measurements, and the stability of I-E. (3) Compare lifetimes of wafers (having different T{sub b}) by various techniques such as QSSPC and transient photoconductive decay using short laser pulses of different light intensity; (4) Make minority-carrier diffusion length (L) measurements by a surface photovoltage technique, and to use T{sub b} and L data to determine diffusivity (D) values for various impurity and defect concentrations, using the relationship L{sup 2} = D* T{sub b}.
Date: May 1, 2008
Creator: Sopori, B.; Rupnowski, P.; Appel, J.; Mehta, V.; Li, C. & Johnston, S.
Partner: UNT Libraries Government Documents Department

Continuous Fiber Ceramic Composite (CFCC) Program: Gaseous Nitridation

Description: Textron has developed a mature process for the fabrication of continuous fiber ceramic composite (CFCC) tubes for application in the aluminum processing and casting industry. The major milestones in this project are System Composition; Matrix Formulation; Preform Fabrication; Nitridation; Material Characterization; Component Evaluation
Date: October 29, 2001
Creator: DiBona, R. Suplinskas G. & Grant, W.
Partner: UNT Libraries Government Documents Department