bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intrinsic and Thermal Stress in Gallium Nitride Epitaxial Films
Authors: Ager J. W. , Suski T. , Ruvimov S. , Krueger J. , Conti G. , Weber E. R. , Bremser M. D. , Davis R. , Kuo C. P. 
Published: April 2011

ABSTRACTStrain in GaN epitaxial layers at room temperature is measured with three complementary methods: Raman spectroscopy (via shifts of phonon frequencies), low temperature photoluminescence (via shifts of band-edge luminescence), and X-ray diffraction (via shifts in lattice spacings). GaN films grown on the c-plane of sapphire tend to be in compression. Increasing the Si-dopant concentration (up to 1019 cm−3) is observed to add compressive strain to the layer. Axially resolved measurements obtained by micro-Raman in 4 μm thick Si-doped films reveal strain relaxation toward the sample surface at Si concentrations above 1018 cm−3. Mg- and Si-doped GaN films on SiC substrates are found to be in tension. An experimental methodology is presented that separates two contributions to the room temperature residual stress in GaN epilayers: (1) the thermal stress due to differences in the thermal expansion coefficients of the epilayer and substrate and (2) the intrinsic stress, which is influenced by the growth conditions. We measure stress as a function of temperature up to 325 C, about one-third of the growth temperature, by monitoring the frequency of the E2 phonon mode by Raman spectroscopy. A high-quality bulk single crystal of GaN is used as a strain-free standard. Over this temperature range, most layers behave elastically; the observed stress trends are well-fit by a thermal expansion model using previous reported values of the thermal expansion coefficients of GaN and the substrates. The intrinsic stress states at the growth temperature for films grown on sapphire and SiC are predicted to be tensile and compressive, respectively, in agreement with the a-plane lattice coefficient mismatch.
Yellow Luminescence and Associated Odmr in Movpe Gan: A Comparison of Defect Models
Authors: Mason P. W. , Dörnen A. , Härle V. , Scholz F. , Watkins G. D. 
Published: April 2011

ABSTRACTTwo positive ODMR resonances are commonly observed on a luminescence band in GaN at 2.2 eV, one identified as a shallow donor, the other currently unidentified. We here report a study of their dependencies on a variety of experimental parameters, including microwave modulation frequency, microwave power, photoexcitation power and photoexcitation energy. ODMR simulations using two theoretical models are compared to experimental results which are consistent with spin-dependent recombination between the two defects, assuming the donor has a spin-lattice relaxation time shorter than the spin-dependent recombination lifetime. The photoexcitation energy dependence suggests that the spin-dependent recombination associated with the 2.2 eV band is not the same recombination that is responsible for the luminescence. This supports the two stage model put forth by Glaser et al. for the luminescence process.
A Model for Indium Incorporation in the Growth of InGaN Films
Authors: Piner E. L. , McIntosh F. G. , Roberts J. C. , Boutros K. S. , Aumer M. E. , Joshkin V. A. , El-Masry N.A. , Bedair S.M. , Liu S.X. 
Published: April 2011

ABSTRACTThe development of high quality indium based III-nitride compounds is lagging behind the corresponding aluminum and gallium based compounds. Potential problems confronting the growth of epitaxial and double heterostructure InGaN will be discussed. A mass balance model is presented describing the competing reaction pathways occurring during the growth of indium containing compounds. Atomic layer epitaxy and metalorganic chemical vapor deposition grown InGaN films will be used to explain this model. Also, the growth parameters leading to the attainment of high InN percentages, reduced indium metal formation, and improved structural and optical properties of indium containing nitrides will be discussed.
Theoretical Study of Group-III-Nitride Alloys
Authors: Kim Kwiseon , Limpijumnong Sukit , Lambrecht Walter RL , Segall B. 
Published: April 2011

ABSTRACTBand gap bowing, structural relaxations, and energies of formation were calculated for the three pseudobinary nitride zincblende alloy systems Al-Ga, In-Ga and In-Al using the full-potential linearized muffin-tin orbital method. The cluster expansion and Connolly-Williams approaches were used to relate calculated band structures and energies of formation of ordered compounds to the behavior of disordered alloys. Effects of bond length and volume variation on those properties are discussed. An interpolation formula for the gap of the full pseudoternary AlxGayInzN system is proposed and tested by separate calculations. Extension of the results to the wurtzite alloys is discussed.
Low-Temperature Metalorganic Chemical Vapor Deposition of Gallium Nitride on (0001) Sapphire Substrates Using a Remote rf Nitrogen Plasma
Authors: Sone Cheolsoo , Hong Kim Min , Hyung Yi Jae , Ok Heur Soun , Yoon Euijoon 
Published: April 2011

ABSTRACTWe report the low-temperature growth of GaN layers on (0001) sapphire substrates by a remote plasma enhanced metal-organic chemical vapor deposition in the temperature range of 500 - 800 $C. Effects of process parameters on the growth of GaN were studied. The structural quality of GaN improved as the growth temperature increased and the rf power decreased. Highly oriented GaN layers could be deposited at fairly low temperatures such as 500 $C under low rf power with low growth rate conditions.
The Influence of Hydrogen Addition on the Chemical Properties of Hydrogenated Aluminum Nitride Films Prepared by RF Reactive Sputtering
Authors: Lee Jai-Young , Yong Yoon-Joong 
Published: April 2011

ABSTRACTHydrogenated aluminum nitride (A1N:H) films have been deposited on the (100) silicon wafers by the RF reactive magnetron sputtering method with H2 gas in addition to an Ar-N2 gas mixture. Stoichiometric A1N films without oxygen impurities can be prepared by adding 10 % H2 to reactive gas, which is proven by Rutherford Backscattering Spectrometry (RBS). The bonding aspects of Al, N, O and H atoms in A1N:H films have been examined by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared (FTIR) to understand the effects of H2 addition. The chemical shift of the binding energies of A1, N and O atoms in A1N:H films from XPS analysis and the change of N-H bonding in FTIR with respect to different partial pressures of H2 gas have been confirmed. The role of H atoms is suggested to facilitate bonding with unbound N atoms in A1N:H films and hinder N-O bonding, thus, reducing oxygen concentration in A1N:H films. Also, the activation energy for the evolution of H2 gas from A1N:H film has been determined to be 0.11 eV/atom through a Kissinger-type analysis by a thermal desorption test using Gas Chromatograph(GC). This result implies that the hydrogen atom in film forms the hydrogen bond.
Thermoelectric Properties of RhSb3 Crystals and Thin Films
Authors: Chen Baoxing , Xu Jun-Hao , Hu Siqing , Uher Ctirad 
Published: April 2011

AbstractRhSb3 belongs to a class of solids called skutterudites which were recently identified as promising novel thermoelectric materials. Our intent was to explore thin film growth of RhSb3 and to assess the thermoelectric properties of such films. RhSb3 films were prepared by electron-beam deposition on silicon and sapphire substrates. Thermopower, electrical resistivity and the Hall effect were measured over the temperature range from 2K to 300K. The data are compared to measurements on single crystals of RhSb3.
UV and Blue Photoluminescence from Silicon Nanocolloids
Authors: Iwasaki Shingo , Kimura Keisaku 
Published: April 2011

AbstractWe have prepared silicon nanocolloids by trapping silicon nanocrystallites produced by a gas evaporation method into an organic liquid. Blue photoluminescence (PL) at a peak maximum around 480 nm from silicon nanocolloids has been observed at room temperature. The external quantum efficiency of blue PL is 0.16 %. A room temperature UV PL has been observed by dropping alkaline solids such as sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2) into silicon nanocolloids. The mechanism of blue and UV PL from silicon nanocolloids is discussed.
Preparation and Characterization of Silicon Nanocrystals in a SiO2 Matrix and Study of Suboxide Stability
Authors: Hinds B. J. , Banerjee A. , Johnson R. S. , Lucovsky G. 
Published: April 2011

AbstractThe kinetics of the decomposition of silicon suboxides (SiOx, x<2) to Sic + SiO2 was studied as a function of composition and post-deposition annealing. Amorphous hydrogenated SiOx films (0.8<x<1.4) were deposited by remote plasma enhanced chemical vapor deposition (RPECVD) and rapid thermal annealed (RTA) at temperatures of 500–1000°C. By monitoring the Si-O infra-red (IR) bond-stretch mode frequency, it was found that at temperatures below 850°C, or at a oxygen poor composition near SiO0.8, the decomposition reaction only proceeded to a metastable form of SiO1.6 + Si. Characterization by Raman and spectroscopie ellipsometry confirm similar trends. Cross sectional transmission electron microscopy (TEM) confirms that Si nanocrystals (Sine) are formed with anneals at 900°C (30 sec). As deposited suboxides show band edge photoluminescence at 1.6 eV which disappears upon annealing at 900°C, indicating a sharp suboxide free interface between Sinc and SiO2 matrix.
The Characteristics and Oxidation of Vapor - Liquid - Solid Grown Si Nanowires
Authors: Westwater J. , Gosain D. P. , Tomiya S. , Hirano Y. , Usui S. , Ruda H. 
Published: April 2011

AbstractThe Vapor - Liquid - Solid (VLS ) technique allows the growth of high aspect ratio Si wires. The Si nanowires formed by this technique can be thinned down by oxidation. This approach allows the formation of very thin Si cores which may be used to research the properties of Si nanostructures. In this work the growth and oxidation of these wires is characterized.In the growth a very thin layer of Au is deposited on a Si (111) surface, silane gas is introduced into the chamber as the Si source gas and the temperature is raised to 300 – 600°C. Initially a catalytically active Au surface phase leads to the growth of a defective epitaxial Si layer. As Au / Si molten alloy balls nucleate and grow in size to approach the threshold size for VLS wire growth, which is determined by the Gibbs - Thomson effect, the epitaxial layer growth rate decreases and a transition to Si nanowire growth occurs. The morphology and width of the wires is strongly dependent on the growth temperature and pressure. At low pressure and high temperature relatively thick well-formed wires grow straight up from the substrate surface along the [111] direction. As the temperature is decreased and the pressure is increased thinner wires (as thin as 10 nm ) grow which tend to exhibit growth defects. A light oxidation yields Si cores which are of the order of 5 nm in diameter.
Limits and Properties of Size Quantization Effects in InAs Self Assembled Quantum Dots
Authors: Schmidt K. H. , Medeiros-Ribeiro G. , Cheng M. , Petroff P. M. 
Published: April 2011

AbstractIn this paper we report on the limits and properties of size quantization effects in InAs self assembled quantum dots (QDs). Size, density and character of the InAs islands are investigated by transmission electron microscopy. The electronic and optical properties of the islands in the coherent and dislocated growth regime are studied using capacitance, photoluminescence, photovoltage and photocurrent spectroscopy. In the data measured with the different techniques, the change in dot size and density as well as the transition from coherent to dislocated island growth is clearly observable. An increasing QD size causes a red shift in the energetic position of the QD features while the density of the islands is reflected in the intensity of the QD signal. The decrease in intensity at high InAs coverage is attributed to dislocated island formation.
Surface Derivatization of Nanocrystalline CdSe Semiconductors
Authors: Lee J.-K. , Kuno M. , Bawendi M. G. 
Published: April 2011

AbstractCdSe quantum dots (QDs) with several different ligands were prepared by ligand exchange reactions of trioctylphosphine oxide (TOPO)/trioctylphosphine selenide (TOPSe) passivated QDs with an excess of new ligands, such as pyridine, 4-picoline, thiophenol, 4-(trifluoromethyl)-thiophenol, and tris(2-ethylhexyl)phosphate. We find that 85–90% of ligands passivating the surface of the QDs are the newly introduced capping species and 10–15% are native TOPO/TOPSe ligands, reflecting the incomplete exchange of the QD surface. Thermal gravimetric analysis (TGA) and quantitative proton NMR measurements show that on average only 30% of surface cadmium atoms are passivated by TOPO/TOPSe. Approximately 1/3 of these native ligands occupy sites too strongly bound to be replaced by ligand exchange reactions.
The Band Edge Luminescence of Surface Modified CdSe Nanocrystallites
Authors: Kuno M. , Lee J. K. , Dabbousi B. O. , Mikulec F. V. , Bawendi M. G. 
Published: April 2011

AbstractWe study the band edge luminescence of CdSe nanocrystallites to determine the origin of this emission. Previous studies have attributed the band edge emission to the recombination of photo-generated carriers trapped in localized surface states. Recently a number of “dark exciton” theories have been proposed which explain the luminescence in terms of recombination through internal core states. To address this issue we modify the surface of CdSe nanocrystallites with a number of organic/inorganic ligands and monitor the effect this has on the energetics of the resonant and non-resonant band edge luminescence. Our results for nanocrystallites passivated with trioctylphosphine oxide (TOPO), ZnS, 4-Picoline, 4-(trifluoromethyl)thiophenol, and tris(2-ethylhexyl)phosphate are in agreement with a dark exciton description of the band edge luminescence.
Nuclear Magnetic Resonance (NMR) of Porous Silicon
Authors: Chang W. K. , Liao M. Y. , Gleason K. K. 
Published: April 2011

AbstractPorous silicon (PS) was characterized by 1H, 19F and 29Si solid-state nuclear magnetic resonance (NMR). On freshly prepared samples, hydrogen contents were between 3 × 1014 and 3 × 1015 per cm2 of PS surface area, while fluorine concentrations were below the detection limit. Cross-polarization (CP) was used to selectively observe the 29Si near the hydrogen passivation. The features of the 29Si NMR spectra are assigned as (O)2(Si)Si-H (-50 ppm), (O)3Si-H (-84 ppm), (Si)3Si-H (-91 ppm), (Si)2Si-H2 (-102 ppm) and (O)4Si (-109 ppm). Changes resulting from low temperature annealing in air and an HF soak were observed by both NMR and infrared spectroscopy. The 29Si NMR line widths for PS fall between those for crystalline silicon and those for amorphous hydrogenated silicon films (a-Si:H), suggesting disorder near the PS surface is intermediate between these extremes. However, comparison of the isotropie chemical shift values shows that the bonding in the disordered regions of PS differs from that found in a-Si:H. In addition, the sharp 29Si NMR resonance observed in the bulk single crystal starting material can not be resolved in the spectra of PS. Thus, well-ordered silicon nanocrystallites in the PS are either several bond-lengths removed from hydrogen or comprise only a small fraction of the PS layer.
Electrochemical and Chemical Deposition of II-VI Semiconductors in Porous Silicon
Authors: Herino R. , Gros-Jean M. , Montes L. , Lincot D. 
Published: April 2011

AbstractThe introduction of II-VI semiconductor compounds into porous silicon layers has been investigated in order to obtain transparent and conducting contacts with the inner surface of the material. CdTe and ZnSe have been electrodeposited cathodically on n type nanoporous electrodes from acidic solutions containing the metallic cations and dissolved oxides of selenium or tellurium. CdS incorporation into p-type porous silicon has been achieved by chemical bath deposition, from solutions containing cadmium complexes and thioacetamid as a sulfur donor. Characterization of the deposits has been performed by SEM observations, X-ray analysis and RBS. Results confirm the penetration of the compounds into the porous films, with small to strong concentration gradients in thickness depending on the deposition method. After deposition and sample drying, the luminescence of CdTe embedded layers has almost disappeared, whereas those containing ZnSe and CdS show a photoluminescence efficiency which is not severely degraded.
Photo-Irradiation-Induced Narrowing of Photoluminescence Spectra from Porous Silicon
Authors: Okamoto M. , Nagao T. , Ooiwa T. , Hatta A. , Ilo T. 
Published: April 2011

AbstractPorous silicon (PS) has been prepared by varying photo-irradiation time in the latter period of anodization, and spectral intensity and width of photoluminescence (PL) have been measured as well as their dependences on current density during the photo-irradiation. Significant differences in PL spectra have been found when the timing of photo-irradiation is varied during the anodization. Sufficient numbers of photo-excited holes are responsible for the formation of PS layers yielding bright and sharp PL. The narrowest FWHM obtained was 0.182eV for a PL peak energy of 1.71eV while the highest peak energy of PL with FWHM < 0.30 eV was 2.16 eV (575 nm).
Quantum Dots as Inorganic DNA-Binding Proteins
Authors: Murphy Catherine J. , Brauns Eric B. , Gearheart Latha 
Published: April 2011

AbstractSemiconductor quantum dots of cadmium sulfide, CdS, are approximately the size of proteins and are photoluminescent in the red, yellow, or green, depending on surface preparation. This photoluminescence is very sensitive to the Nature and amount of adsorbates. We have found that DNAs with intrinsic curvature adsorb more strongly to the surface of 47 Å CdS quantum dots, as judged by concentration-dependent changes in photoluminescence. The binding constants we obtain are similar to those found for nonspecific protein-DNA interactions. The surface groups of the CdS substrate also influence DNA adsorption. Thus these protein-sized colloidal particles can be used in chemical sensing applications for curved or kinked DNA; DNA with unusual structures is thought to influence biological function such as transcription.
D.C Current-Voltage Characteristics and Admittance Spectroscopy of an Al-Porous Si Barrier
Authors: Khirouni K. , Bourgoin J. C. , Borgi K. , Maaref H. , Deresmes D. , Stiévenard D. 
Published: April 2011

AbstractWe present the temperature and frequency dependence of the current-voltage (I-V) characteristics of Al barriers deposited on porous Si grown on p-type Si substrates. These barriers exhibit a rectifying behaviour when the temperature is higher than 250 K. The I-V characteristics can be understood by a conduction in porous Si taking place via free electrons thermally excited from Pb centers associated with the existence of a SiO2-Si interface and via hopping between these Pb centers.
Elaboration and Light Emission Properties of Low Doped p-Type Porous Silicon Microcavities
Authors: Lérondel G. , Ferrand P. , Romestain R. 
Published: April 2011

AbstractWe account for the elaboration of Bragg reflectors and microcavities based on efficiently luminescent porous silicon. A characterisation of very thin porous silicon layers obtained with current densities of formation varying from 1.5 mA to 300 mA is presented. The resulting refractive index variation (typically from 1.37 to 1.86 at 700 nm) enables the elaboration of high quality Bragg reflectors and Fabry-Perot filters from the yellow to the near infrared. Although low doped p-type porous silicon develops rougher interfaces than highly doped p-type porous silicon, its better luminescence efficiency has enabled us to elaborate microcavities with a strong emission in a narrow band.
Microcrystalline Silicon Solar Cells at Higher Deposition Rates by the VHF-GD
Authors: Torres P. , Meier J. , Goetz M. , Beck N. , Kroll U. , Keppner H. , Shah A. 
Published: April 2011

AbstractA 7.7 % single junction cell efficiency for an entirely microcrystalline silicon (μc-SiH) device has recently been reported by our group [1]. This was achieved by applying the purifier technique, a technique which is indeed easier to handle than the earlier used “microdoping” approach. The purpose of the present paper is twofold: First to show in detail the impact on device performance when a gas purifier is used; and second to illustrate that the deposition rate of the active, absorbing i-layer can be increased from the former 1.55 Å/s up to 4.3 Å/s while still maintaining reasonable device performances. In the latter case a first n-i-p solar cell structure on an aluminium sheet could be fabricated with an efficiency of 4.9 %.
Low-Temperature Formation of Device-Quality Polysilicon Films by cat-CVD Method
Authors: Matsumura Hideki , Heya Akira , Iizuka Ritsuko , Izumi Akira , He An-Qiang , Otsuka Nobuo 
Published: April 2011

AbstractPolycrystalline silicon (poly-Si) films are deposited at temperatures lower than 300–400°C by the cat-CVD method. In the method, a SiH4 and H2 gas-mixture is decomposed by catalytic cracking reactions with a heated tungsten catalyzer placed near substrates. Carrier transport, optical and structural properties are investigated for this cat-CVD poly-Si. The films show both large carrier mobility and large optical absorption for particular deposition conditions. The cat-CVD poly-Si films are found to be one of the useful materials for thin film transistors and thin film solar cells.
Molecular Dynamic Computer Simulation of Elastic and Plastic Behavior of Nanophase Ni
Authors: Van Swygenhoven H. , Caro A. 
Published: April 2011

ABSTRACTMolecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples with several mean grain size in the range 3–5 nm are reported. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young modulus are calculated from stress-strain curves and the onsett of plastic deformation is discussed. At higher loads substantial difference in the plastic behaviour with respect to the coarse grain counterpart is observed: among the mechanism responsible for the deformation, grain boundary sliding and motion, as well as grain rotation are identified. An interpretation in terms of grain boundary viscosity is proposed and a linear dependence of strain rate with the inverse of the grain size is obtained.
Optical Properties of Metal Wire Array Composites
Authors: Luo Laura , Huber T. E. 
Published: April 2011

ABSTRACTAccording to effective medium theories, electrically conducting composites consisting of parallel metal wires embedded in a transparent dielectric can propagate light in the direction of the wire length. We have prepared densely packed arrays (76% volume fraction) of 10-μm diameter indium wires by high pressure injection of glass microchannel plates. For wavelengths longer than 100 μm (k<100 cm−1) the absorption of the wire array is almost three orders of magnitude smaller than that of an indium foil of equal thickness. The measured absorption increases as k0.45±0.07 and can be accounted for by including magnetic dipole effects.