bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic properties of CeOs4Sb12
Authors: Galvan Donald
Published: April 2011

CeOs4Sb12 is a very interesting material due to the diversity of physical properties which could be dedicated to industrial applications. With this goal in mind, electronic structural calculations were performed in order to provide information regarding its properties. The energy bands yielded information regarding its semiconductor behavior as well as a mini gap of the order of 0.45 eV between the valence and conduction bands. Moreover, total and projected density of states yielded information of a possible hybridization between Ce f-, Os d- and p-, with Sb p-orbitals. Hence, this compound could be considered a likely candidate as a thermoelectic material
Thermoelectric Properties of Tl-X-Te (X=Pb, Sn, Ge) Systems
Authors: Kosuga Atsuko , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: April 2011

Polycrystalline-sintered samples of Tl2GeTe3, Tl4SnTe3, and Tl4PbTe3 were prepared by a solid-state reaction. Their thermoelectric properties were evaluated at temperatures ranging from room temperature to ca. 700 K by using the measured electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ). Despite their poor electrical properties, the dimensionless figure of merit ZT of all the compounds was relatively high, i.e., 0.74 at 673 K for Tl4SnTe3, 0.71 at 673 K for Tl4PbTe3, 0.29 at 473 K for Tl2GeTe3, due to the very low lattice thermal conductivity of the compounds.
Synthesis and Thermoelectric Properties of CeyRuxIr4−xSb12) Filled Skutterudite Compounds
Authors: Jewell April D. , Paik Jong-Ah , Caillat Thierry
Published: April 2011

Radioisotope Thermoelectric Generators (RTGs) have proved to be reliable, long-lived sources of electrical power that have enabled the conduct of a number of important NASA deep space missions since 1961. Past RTGs have used two types of thermoelectric materials: PbTe/TAGS and SiGe. In an effort to further improve both the thermoelectric efficiency and specific power of the next generation of RTGs, JPL is investigating a number of potential high-efficiency, high-temperature thermoelectric materials that could operate at a hot-side temperature of up to 1275 K. Among the materials being studied are the refractory CeyRu4−xIrxSb12 filled skutterudite compounds. We have synthesized polycrystalline samples for x ≤ 1.5 by a powder metallurgy technique. Dense samples have been hot-pressed from the pre-reacted powders and characterized by a variety of techniques including electron probe microanalysis, differential thermal analysis and thermogravimetic analysis. Seebeck coefficient, electrical resistivity, Hall coefficient, and thermal conductivity measurements have been conducted on the samples from room temperature to 1275 K. Results show that the samples are phase stable up to 1275 K. The results of the transport property measurements are presented and discussed.
Multi-scale Rule-of-Mixtures Model of Carbon Nanotube/Carbon Fiber/Epoxy Lamina
Authors: Frankland Sarah-Jane , Riddick J. C. , Gates T. S.
Published: April 2011

A unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes is modeled with a multi-scale method, the atomistically informed rule-of-mixtures. This multi-scale model is designed to include the effect of the carbon nanotubes on the constitutive properties of the lamina. It included concepts from the molecular dynamics/equivalent continuum methods, micromechanics, and the strength of materials. Within the model both the nanotube volume fraction and nanotube distribution were varied. It was found that for a lamina with 60% carbon fiber volume fraction, the Young’s modulus in the fiber direction varied with changes in the nanotube distribution, from 138.8 to 140 GPa with nanotube volume fractions ranging from 0.0001 to 0.0125. The presence of nanotube near the surface of the carbon fiber is therefore expected to have a small, but positive, effect on the constitutive properties of the lamina.
ESR Spin Resonance on Carbon Nanofibers
Authors: Chipara Mircea , Hauge Robert H. , Fan Hua , Booker Richard , Peng Haiqing , Hwang Wen Fang , Zaleski Jeffrey M. , Smalley Richard E.
Published: April 2011

Electron spin resonance investigations on the angular dependence of carbon nanotubes are reported. It is proved that the resonance line is a convolution of three lines one due to electron delocalized over carbon nanotubes, the second assigned either to amorphous carbon or to conducting electrons in interaction with metallic impurities, and the last one originating from catalyst residues.
Ion Desorption by Inner-shell Excitation and Photodegradation of Poly(vinylidene fluoride)
Authors: Okudaira Koji , Kobayashi Eiichi , Kera Satoshi , Mase Kazuhiko , Ueno Nobuo
Published: April 2011

Auger electron spectra (AES) and Auger electron photo-ion coincidence (AEPICO) spectra of poly(vinlylidene fluoride) (PVDF) were observed to study the mechanism of effective fluorine ion (F+) desorption by irradiation of photons corresponding to the transition from F 1s to s(C-F). In the AES at photon energy (hυ) = 690.3 eV (from F1s to |σ|(C-F)), the spectator-Auger shift is about 3 eV. At hn = 690.3 eV the contribution of spectator Auger electron to the observed Auger spectrum is large. In the F+ AEPICO spectra at hυ = 690.3 eV an intense peak appears. The peak positions of the F+ AEPICO spectra are in agreement with those of the Auger spectra. These results indicate that the mechanism for effective F+ ion desorption induced by the transition from F1s to σ(C-F) occurs through the spectator-Auger processes. The efficiency of ion desorption depends on the electronic structure of the spectator-Auger final state.
Fe-Core/Au-Shell Nanoparticles: Growth Mechanisms, Oxidation and Aging Effects
Authors: Liu Kai , Cho Sung-Jin , Kauzlarich Susan M. , Idrobo J. C. , Davies Joseph E. , Olamit Justin , Browning N. D. , Shahin Ahmed M. , Long Gary J. , Grandjean Fernande
Published: April 2011

We report the chemical synthesis of Fe-core/Au-shell nanoparticles (Fe/Au) by a reverse micelle method, and the investigation of their growth mechanisms and oxidation-resistant characteristics. The core-shell structure and the presence of the Fe and Au phases have been confirmed by transmission electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Mössbauer spectroscopy, and inductively coupled plasma techniques. Additionally, atomic-resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope have been used to study details of the growth processes. The Au-shells grow by nucleating on the Fe-core surfaces before coalescing. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The magnetic moments of such nanoparticles, in the loose powder form, decrease over time due to oxidation. The less than ideal oxidation-resistance of the Au shell may have been caused by the rough Au surfaces. In a small fraction of the particles, off-centered Fe cores have been observed, which are more susceptible to oxidation. However, in the pressed pellet form, electrical transport measurements show that the particles are fairly stable, as the resistance and magnetoresistance of the pellet do not change appreciably over time. Our results demonstrate the complexity involved in the synthesis and properties of these heterostructured nanoparticles.
Modeling of Coarsening Processes In Patterned Systems
Authors: Jhon Mark , Glaeser Andreas M , Chrzan Daryl C
Published: April 2011

Although particle coarsening has been studied for over a century, it remains an active area of materials science research. The current work presents a theoretical analysis of the degradation of regular arrays of spherical particles through diffusional interaction. In order to understand the onset of coarsening, a linear stability analysis is performed on a simple square lattice of particles. It is predicted that particles will dissolve in a spatially ordered manner. The active transport mechanism plays a strong role in the selection of the coherent growth modes.
Formation, evolution and degradation of nanostructured covalent thin films deposited by Low Energy Cluster Beam Deposition
Authors: Compagnini Giuseppe , D'Urso Luisa , Scalisi A. Alessandro , Altamore Corinna , Puglisi Orazio
Published: April 2011

Low Energy Cluster Beam Deposition (LECBD) is considered an intriguing technique to obtain thin layers with well defined structures at the nano- and meso-scale levels, allowing novel optical, electronic and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with “in situ” techniques in order to study their original composition and their evolution once exposed to reactive gases. In this work we present a general overview and some results on the formation evolution and deposition of silicon and carbon cluster beams produced using a laser vaporization source.
Large Area Coatings for Architectural Glass – Design, Manufacturing, Process Faults
Authors: Ridealgh John A
Published: April 2011

The physical properties of architectural sputtered coatings are considered in the context of their design, manufacture, transport and processing. The design constraints of high optical and thermal performance lead to the use of thin metal layers in interference coating stacks. This, in turn, determines the chemical and mechanical property challenges. In-service examples of film failure are presented along with practical countermeasures. Laboratory methods for ranking development coating systems are also discussed.
Formation of coherent structures and mechanical properties of AlN/TiN multilayers
Authors: Allidi G. , Medjani Farida , Sanjines Rosendo , Karimi Ayat
Published: April 2011

AlN/TiN multilayered thin films with layer thickness ranging from 1 nm to 50 nm were synthesized using rf magnetron sputtering at 400°C. Two series of samples were prepared at the substrate bias of Vb = −25 V and −100 V to modify growth texture of individual layers and verify its influence on the formation of coherent structures. XRD and TEM observations showed that in large period films (tc ≥ 30 nm) each constituent grows under its own kinetic, leading to the formation of nano-crysatlline film randomly oriented with no pronounced texture. Decreasing progressively the layer thickness favours the alignment of (0002) basal plane of w-AlN on (111) plane of TiN, and results in development of strong (111) texture, prerequisite for stabilisation of c-AlN and the formation of epitaxial coherent structures. The degree of crystallographic coherence was found to be higher in TiN(111) oriented films than for TiN(002) textured films. The increase of hardness coincides with the structure transition from a randomly oriented nanocrystalline films to a highly (111) textured multilayers, and the maximum hardness was obtained for epitaxially coherent nanolayers.
Plasma Surface Modification of Polymeric Materials
Authors: Razavi Ali
Published: April 2011

This study was undertaken to improve the bonding of fluorinated and non-fluorinated polymers to acrylic and silicone based adhesives. The polymeric materials were exposed to plasma which is comprised of methane and a second gas selected from air, Oxygen and Nitrogen or a mixture thereof. By application of surface analysis (XPS), the optimized functionality can be incorporated in the surface of desired polymers to enhance the bond ability of prepared films for pressure sensitive tape applications. Perfluoroalkoxy-tetrafluoroethylene copolymer PFA, fluorinated ethylene-propylene FEP, Polytetrafluoroethylene PTFE, and Polyester materials were exposed to this plasma. The treated samples were coated with adhesives and the adhesion to steel, holding power and other properties associated with tapes performance were studied.
Waterproof coating on nonlinear optical crystal surfaces by photo–oxidation of silicone oil
Authors: Sato Nobuhiro , Sato Yuji , Okamoto Yoshiaki , Murahara Masataka
Published: April 2011

Organic silicone oil was photo–chemically oxidized to change into SiO2 by using a ultraviolet (UV) excimer lamp, which developed an over–coating for a nonlinear optical crystal.

In general, nonlinear optical crystals are used as a wavelength conversion element for laser. The crystals are, however, deliquescent and absorb moisture in the air, which causes clouding. They need heating in the oven to prevent it. It is desired to develop a protective film on the nonlinear optical crystals so as to be waterproof and transmit UV rays. We have, then, developed the waterproof and protective film on a KH2PO4 (KDP) surface, which was photo–chemically oxidized by using a silicone oil and Xe2 excimer lamp. The silicone oil was spin–coated on the KDP crystal surface, and then the Xe2 excimer lamp was vertically irradiated to the crystal surface. The O atoms in the air were photo–excited with the UV photon to generate high active O atoms. At the same time, the C—H and the Si—C bonds of the silicone oil were photo–dissociated because the photon energy of the UV photon is higher than the bonding energies of the C—H and Si—C. The siloxane of the silicone oil was consequently linked with the O2 that had been absorbed on the crystal surface to form SiOn. As a result, the SiO2 film was formed on the KDP crystal surface by the photo–oxidation of silicone oil.

The infrared spectroscopy analysis (ATR-FTIR) was carried out to investigate the modified film. The results showed that as the time of lamp irradiation extended, the absorption peak of the —CH3 groups at 2900 cm−1 decreased, but the absorption peak of the —SiO groups at 1050cm−1 increased. At the lamp irradiation time of 90 minutes, the UV transmittance of the treated silicone oil improved to 88.9 % at the 260 nm, which is the wavelength of the fourth harmonic generation, while that of the untreated silicone oil was 56 %.

The treated and untreated KDP crystals were tested for their waterproofing. The untreated crystal was completely dissolved thirty minutes after soaking in the water, and on the contrary, the KDP crystal with the film coating has neither been dissolved nor gotten cloudy for three months when soaking in water.
Micro-Raman Evaluation of Polycrystalline Silicon MEMS Devices
Authors: Serrano Justin R. , Phinney Leslie M. , Kearney Sean P.
Published: April 2011

Micro-Raman spectroscopy is a valuable tool for thermometry of operational polysilicon MEMS devices. By using the temperature-calibrated response of the optical phonon peak of the polysilicon Raman signature and the micron-scale spatial resolution achieved with a 488 nm Ar+ laser Raman probe, we have obtained spatially resolved steady-state thermal profiles of Joule-heated thermal flexure actuators. The measured thermal profiles are further compared to one-dimensional numerical models of the thermal response of the electrically heated devices.
Role of Fe and Ni Nanoparticles on Mechanical Properties of Alumina Thin Films deposited by Laser Ablation
Authors: Yarmolenko Sergey , Neralla Sudheer , Kumar Dhananjay , Sankar Jag , Liu Fude , Duscher Gerd
Published: April 2011

This paper reports our recent work on the improved mechanical properties of alumina thin films with embedded Fe and Ni nanoparticle layers. The Fe/Ni nanoparticles-alumina composite thin films have been deposited using a multi-target pulsed laser ablation technique. Every film consists of 10 layers of alumina and 9 intermediate layers of Fe or Ni nanoparticles. Alumina layer thickness kept constant (∼22 nm) and total thickness of multilayered films was in range 220-280 nm depending on metal deposition time. Composite thin films were deposited at six different substrate temperatures in the range 200-800°C. The mechanical properties measurements, performed by nanoindentation in continuous stiffness mode and applying Nix-Bhattacharya (hardness H) and King's model (Young's modulus E) for film-only properties, have shown that pure alumina films deposited at temperatures 200-500°C are relatively soft (H = 15 GPa, E = 190 GPa), while films deposited at ≥600°C are significantly harder (H = 32 GPa, E = 320 GPa). Grazing incidence XRD (GIXRD) data indicated that γ-alumina peaks exist in high temperature samples while alumina films deposited at ≥500°C were amorphous. Embedding Ni and Fe nanoparticle layers at 500°C led to significant increase of H and E (31 GPa and 365 GPa with Fe and 33 GPa and 380 GPa with Ni) and appearance of γ-alumina peaks in GIXRD. Embedding on metal nanoparticle layers does not change mechanical properties of alumina films deposited at 200°C, and significant hardening of metal containing films starts at 400°C. These results suggest that metal nanoparticles have a catalytic effect on the growth of alumina thin films with enhanced crystallinty. The effect of Ni and Fe nanoparticle size on mechanical properties of thin films has been studied times at substrate temperature 500°C using eight different metal deposition. HRTEM data have shown that metal nanopartiles have uniform particle size distribution and inter-particle separation in the layer. Size of Ni and Fe nanoparticles with highest effect on mechanical properties was 4 -6 nm.
3.3 μm high brightness LEDs
Authors: Matveev Boris A. , Zotova Nonna V. , Il'inskaya Natalya , Karandashev Sergey A. , Remennyi Maxim A. , Stus' Nicolay M. , Kovchavtsev Anatoly P. , Kuryshev Georgii L. , Polovinkin Vladimir G. , Tarakanova Natalya
Published: April 2011

Deep mesa etching and surface roughening have been implemented to InAs flip-chip LEDs emitting at 3300 nm (300 K). Near field and power measurements confirmed the output power enhancement of about 2 and brightness increase with and equivalent to a black body temperature of about 1250 K.
Investigation of Surface Passivation in InAs/GaSb Strained-Layer-Superlattices Using Picosecond Excitation Correlation Measurement and Variable-Area Diode Array Surface Recombination Velocity Measurement
Authors: Zhu Zhimei , Plis Elena , Amtout Abdenour , Bhattacharya Pallab , Krishna Sanjay
Published: April 2011

The effect of ammonium sulfide passivation on InAs/GaSb superlattice infrared detectors was investigated using two complementary techniques, namely, picosecond excitation correlation (PEC) measurement and variable-area diode array (VADA) surface recombination velocity (SRV) measurement. PEC measurements were conducted on etched InAs/GaSb superlattice mesas, which were passivated in aqueous ammonium sulfide solutions of various strengths for several durations. The PEC signal's decay time constant (DTC) is proportional to carrier lifetimes. At 77 K the PEC signal's DTC of the as-grown InAs/GaSb superlattice sample was 2.0 ns, while that of the unpassivated etched sample was reduced to 1.2 ns by the surface states at the mesa sidewalls. The most effective ammonium sulfide passivation process increased the PEC signal's DTC to 10.4 ns. However it is difficult to isolate surface recombination from other processes that contribute to the lifetime using the PEC data, therefore a VADA SRV measurement was undertaken to determine the effect of passivation on surface recombination. The obtained SRV in the depletion region of the InAs/GaSb superlattice and GaSb junction was 1.1×106 cm/s for the unpassivated sample and 4.6×105 cm/s for the passivated sample. At 77 K the highest R0A value measured in our passivated devices was 2540 W cm2 versus 0.22 W cm2 for the unpassivated diodes. The results of the lifetime, the SRV and the R0A measurements indicate that ammonium sulfide passivation will improve the performance of InAs/GaSb superlattice infrared detectors.
On the nucleation of GaP/GaAs and the effect of buried stress fields
Authors: Zelcovit João Guilherme , Bortoleto José Roberto R. , Bettini Jefferson , Cotta Mônica
Published: April 2011

We have recently shown that spatial ordering for epitaxially grown InP dots can be obtained using the periodic stress field of compositional modulation on the InGaP buffer layer. The aim of this present work is to study the growth of films of GaP by Chemical Beam Epitaxy (CBE), with in-situ monitoring by Reflection High Energy Electron Diffraction (RHEED), on layers of unstressed and stressed GaAs. Complementary, we have studied the role of a buried InP dot array on GaP nucleation in order to obtain three-dimensional structures. In both cases, the topographical characteristics of the samples were investigated by Atomic Force Microscopy (AFM) in non-contact mode. Thus vertically-coupled quantum dots of different materials have been obtained keeping the in-place spatial ordering originated from the composition modulation.
Growth of GaAs on (100) Ge and Vicinal Ge Surface by Migration Enhanced Epitaxy
Authors: Tanoto Hendrix , Yoon Soon Fatt , Loke Wan Khai , Fitzgerald Eugene A. , Dohrman Carl , Narayanan Balasubramanian , Tung Chih Hang
Published: April 2011

In this paper, we present GaAs/Ge heteroepitaxy grown by RIBER32 solid-source Molecular Beam Epitaxy (SSMBE) with initial GaAs nucleation by migration-enhanced epitaxy (MEE) technique. We look at the influence of substrate temperature during the MEE and the influence of Ge surface orientation to the quality of the GaAs layer. Three samples were grown for this study; the first two samples, sample A and B, have surface orientation of (100) 6° offcut towards (111) plane. This surface orientation was chosen as to achieve double-atomic steps surface that is crucial to suppress anti-phase domain (APD) formation. These samples were then subjected to different temperature during the MEE process, 450°C for sample A and 250°C for sample B. The third sample, sample C, has the same MEE substrate temperature as sample A, which is 450°C but with nominal (100) surface orientation. The growth conditions and structure of the layers after the MEE process were kept constant across the three samples.

We examine the structures and the optical quality of the samples by cross-sectional Transmission Electron Microscope (XTEM) and 5K photoluminescence (PL). Analyzing the XTEM images of sample A and B, it is found that the APD still appear in sample A while it is suppressed totally in sample B. It is also observed from sample A XTEM image that two APDs propagating with 45° and 135° angle, as measured from the GaAs/Ge interface, could meet with each other at certain layer thickness leading to self-annihilation. However, some of the self-annihilations took place only after the APDs propagated hundreds of nanometers in the GaAs layer, producing large undulation in the layer. As for sample B, we believe that the APD suppression is mainly due to the much lower nucleation temperature. At such low temperature, As dimers are adsorbed onto the substrate surface more readily with negligible re-evaporation. This ensures complete As coverage on the double-atomic steps Ge surface and minimize As vacancies that may act as defect initiation centers. Furthermore, the low substrate temperature shortens the migration distance of Ga adatoms, minimizing their adsorption into the kinks and step edges, resulting in two-dimensional growth mode instead of step-flow growth mode.

Meanwhile, XTEM image of sample C shows APDs that propagated almost perpendicularly to the GaAs/Ge interface, making it unlikely for the self-annihilation mechanism to take event. It is understood that the direction of propagation of the APD relies on the atomic steps reconstruction of the Ge starting surface. In the case of single atomic-step surface, the APDs propagate almost perpendicularly to the interface. Finally, the 5K PL spectra of the embedded InGaAs single quantum-well in all the samples clearly demonstrate that the best optical quality comes from sample B; which we believe mainly because of the total suppression of APD, leading to much improved layer quality.
Evaluation on Defects of Er and Yb Implanted Al070Ga030As by Using Positron Annihilation Spectroscopy
Authors: Arai Tomoyuki , Uekusa Shin-ichiro , Uedono Akira
Published: April 2011

The influence on defects of Er implanted Al0.70Ga0.30As was studied, using standard Positron Annihilation Spectroscopy (PAS) and Photoluminescence (PL) technique. The incident energy of mono-energetic positrons was implanted from 0.1 eV to 30 keV. The characterization of un-doped Al0.70Ga0.30As and Al0.70Ga0.30As:Er,Yb as implanted, and Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C were successfully studied by using PAS technique. Into the incident energy around 5keV, the shape parameter of Al0.70Ga0.30As:Er,Yb annealed ranging from 500 to 900 °C was decreased and the PL intensity also increased in response to the annealing temperature ranging from 500 to 900 °C.
Prediction of Young's Moduli of Low Dielectric Constant Materials by Atomistic Molecular Dynamics Simulation
Authors: Choi Hyuk Soon , Lee Taebum , Lee Hyosug , Kim Jongseob , Hong Ki-Ha , Kim Kwang Hee , Shin Jaikwang , Shin Hyun Jin , Jung Hyeon Dam , Choi Seung Hoon
Published: April 2011

The interests of low-k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits are well known in the semiconductor industry. Mechanical properties of low-k film are currently the main issues. Improved hardness and modulus are desirable because, when building a multilayered stack and doing sequential processing, films go through chemical mechanical planarization. In this proceeding, we reports the Young's moduli of the typical low k materials, and the effects of various factors for Young's moduli of materials, such as, structures of precursors, density, and porosity. Using atomistic molecular dynamics simulation with experimental measurements, the Young's moduli of films of amorphous silicon oxide in which 25% of Si-O-Si chains were replaced by Si-(CH3 H3C)-Si, Si-CH2-Si, Si-(CH2)2-Si, Si-(CH2)3-Si, Si-(CH2)4-Si, Si-(CH2)6-Si, were measured and analyzed. The predicted trends of Young's moduli of films formed by above precursors are in good consistent with those observed from experiments. The Young's moduli of materials are largely dependent on the densities of materials. Young's modulus of material increases as the density of the material increases. The chemical properties, chain length, and connectivity of material take effects on the Young's modulus of material. Given the same densities of material the smaller number of cavities per unit volume the material has, the lower Young's modulus it shows. Based on the results, the method of predict mechanical properties of materials by the conjunction of basic experimental measurements and atomistic simulation will be discussed.
Thermal stability of nickel-cobalt multilayer silicide
Authors: Han Kil Jin , Cho Yu Jung , Oh Soon Young , Kim Yong Jin , Lee Won Jae , Lee Hi Deok , Kim Yeong-Cheol
Published: April 2011

In this study, we have investigated the structure of nickel-cobalt silicide to understand its behavior at high temperature. Nickel-cobalt silicide was formed after two-step RTP at 500°C and 700°C respectively. We could observe by TEM that nickel-cobalt silicide consists of a structure which seems to be a Ni-Co-Si ternary phase. No nickel silicide phases and cobalt silicide phases were detected in nickel-cobalt silicide by XRD. From XPS depth profile, we could confirm that there is a cobalt composition gradient along the silicide.
Role Of Active Oxygen Species On Growth Of ZnO Using RF-PAMBE
Authors: Durbin Steven M. , Lee William C. T. , Allen Martin , Miller Paul , Reeves Roger J.
Published: April 2011

The effect of different oxygen species on the RF plasma-assisted molecular beam epitaxy growth of ZnO films has been investigated. By varying the geometry of the aperture plate and also the RF power, the relative atomic content in the discharge was altered, and this is found to be corre-lated to the film quality. Further, growth rate studies performed in tandem with in-situ laser interferometry suggest that stoichiometric conditions may not result in saturation of growth rates.
ZnO Light-Emission Array Fabricated into Nanometer-scale Pits on Silicon Substrate
Authors: Ohashi Naoki , Sakaguchi Isao , Sekiguchi Takashi , Haneda Hajime , Kobayashi Kazuyoshi , Masauda Hidetoshi , Chazono Hirokazu , Fujimoto Masayuki
Published: April 2011

A nanometer-scale ZnO light emission array device was fabricated using the multi-level metallization technique of the CMOS process. Square arrays of pits with an inverted pyramid shape made from {111}Si planes were formed on a (100)Si substrate using selective etching. ZnO was deposited on the substrate by chemical vapor deposition (CVD), and the surface of the deposited ZnO film was carefully polished by chemical mechanical planarization (CMP). As a result, ZnO-filled nanometer-scale arrays were obtained after removing the ZnO layer except for the ZnO in the pits by CMP. Cathodoluminescence (CL) from the ZnO arrays was observed.
Optical Properties of Zinc Oxide Quantum Dots Embedded Films by Metal Organic Chemical Vapor Deposition
Authors: Tan S. T. , Sun X. W. , Zhang X. H. , Chen B. J. , Chua S. J.
Published: April 2011

Zinc oxide (ZnO) quantum dots (QDs) embedded films were fabricated on silicon substrates by metal organic chemical vapor deposition at 350°C. The QDs can be obtained in a matrix of amorphous ZnO films by introducing a large amount of precursors. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission is due to the quantum confinement effect of the QDs. The quantum confinement effect of the QDs disappears after the post-growth annealing due to the ripening of QDs.
Structural Studies of ZnO Calcined with Transition Metal Oxides
Authors: Noice Lori , Seipel Bjoern , Grathoff Georg , Gupta Amita , Moeck Peter , Rao V. K.
Published: April 2011

Powder X-ray diffraction analyses of Mn-and Cu-doped ZnO powders calcined at 500˚C, show shifts in the wurtzite type semiconductor's lattice constants and unit cell volume which correspond to the nominal concentrations of transition metal dopants. Marked reductions in the a-lattice constant and unit cell volume for a small concentration of Cu dopants, which is not maintained upon increased Cu concentration, suggest a change in the copper ion hybridization state due to the dopant concentration. In all the samples, only ZnO and CuO phases were detected, aiding the ascertainment of any ferromagnetic response from the samples as arising from the formation of a true dilute magnetic semiconductor.
Roles of Laser-Ablation of Mn in Initial Stage of Growth of ZnO Nanorods by Chemical Vapor Deposition
Authors: Hirate Takashi , Miyashita Hiroshi , Kimpara Takashi , Takizawa Kazumoto , Satoh Tomomasa
Published: April 2011

We studied on effects of laser ablation on morphology of ZnO nanorods fabricated by low-pressure thermal chemical vapor deposition combined with laser ablation of Mn. In this paper, we studied on the effects of laser-ablation time period and energy density of laser beam at an initial stage of growth of ZnO nanorods. Both of laser ablation and chemical vapor deposition are started simultaneously and the laser ablation is stopped on the way of growth of ZnO nanorods. After the laser ablation is stopped, only chemical vapor deposition is continued. It is concluded from the experimental results that even if laser-ablation time period is only 30 sec and energy density of laser is only 0.023 Joule/cm2/pulse, the laser ablation shows remarkable effects on growth of ZnO nanorods.
Composition modulation and local structure in strained diluted GaInNAs nitride alloy thin layers on GaAs substrates
Authors: Metsue Arnaud , Priester Catherine
Published: April 2011

The theoretical study reported here is devoted to diluted GaInNAs nitride alloys, and focuses on correlation between local chemical atomic neighborhood and atomic distances. The model used is Valence Force Field approximation, and we model a periodic Ga1−xInxNyAs1−y alloy film deposited on a GaAs substrate. The surface is dimerised (for simplicity we consider 2×1 anion rich surfaces). First starting from a random film, first and second nearest neighbor distances are calculated, and the corresponding histogram drawn. Then a pseudo-annealing process is simulated by allowing the N atoms to choose their optimal location. This pseudo-annealing strongly enhances the number of In-N bonds, in agreement to experimental studies. From this statistical study, fine structure of each peak of the histograms is shown to be not directly related to a given surrounding chemical distribution up to 3rd nearest neighbors. The positions (in distance) of the peaks appear not to be modified by alloy composition nor alloy segregation, which only alter relative intensities and peak shapes. Last, we consider stripes of In-rich and In-poor zones: calculated energy variations show a strong tendency for N atoms to completely desert In-poor zones.
GaNAsBi Semiconductor Alloy with Temperature-Insensitive Bandgap
Authors: Yoshimoto Masahiro , Haung Wei , Feng Gan , Oe Kunishige
Published: April 2011

GaNyAs1−x−yBix alloys were grown by molecular beam epitaxy (MBE) using solid Ga, Bi, and As sources and nitrogen radicals generated from N2 in rf plasma. To achieve Bi incorporation into the epilayer, As flux was adjusted in a limited range on the brink of As shortage on the growing surface. GaNyAs1−x−yBix alloys lattice-matched to GaAs substrates with different photoluminescence (PL) peak energies were obtained. The GaNyAs1−x−yBix alloy lattice-matched to GaAs turned out to have the structure of Ga(N0.34Bi0.66)zAs1−z. The PL spectra showed that the PL peak energy of GaNyAs1−x−yBix alloy decreased with increasing Bi and N contents with redshift coefficients of ∼62 meV/%Bi and ∼130 meV/%N, respectively, at room temperature. The temperature dependence of the PL peak energy for GaNyAs1−x−yBix in the temperature range of 150∼300 K is much smaller than that of InGaAsP. The temperature coefficients of GaNyAs1−x−yBix bandgaps were governed by the GaBi molar fraction and decrease with increasing GaBi molar fraction.
Growth and Characterization of InGaNAs Quaternary Alloys for the Fabrication of Long Wavelength MSM Photodetectors on GaAs Substrates
Authors: Higgins Erle , Noad Julian , Gouin Francois , Coulas David
Published: April 2011

In this paper, the optical and electrical properties of both as-grown and annealed thick InxGa1−xNyAs1−y layers grown by metal organic chemical vapour deposition (MOCVD) are presented. Through careful control of the trimetylyindium (TMIn), dimetylyhydrazine (DMHy), trimethylgallium (TMGa) and arsine (AsH3) precursors, lattice matching conditions were achieved for epitaxial layers containing up to 3% nitrogen (0≤y≤0.03) and 11% indium (0≤x≤0.11) with bandgap wavelengths to 1.3 μm. Nomarski optical microscopy and double crystal x-ray diffraction (XRD) measurements are used to investigate surface morphology, material quality and lattice-matched conditions. There is little or no 10K photoluminescence from the as-grown layers; alloy activation through rapid thermal annealing must be performed to obtain observable photoluminescence peaks. Annealing is also performed to reduce the resistivity of the as-grown layers. Once annealed, the undoped layers exhibited p-type carrier concentrations of 5.5×1017 cm−3 and mobilities of 50 cm2/Vs. The DC and frequency response performance characteristics of metal-semiconductor-metal (MSM) photodetectors fabricated on both as-grown and annealed InGaNAs layers are examined and compared to similar structures fabricated using GaAs and InGaAs/InP epitaxial materials.
Optimization of SiGe Graded Buffer Defectivity and Throughput by Means of High Growth Temperature and Pre-Threaded Substrates
Authors: Erdtmann Matthew , Currie Matthew T. , Woicik Joseph C. , Black David
Published: April 2011

Dislocation glide kinetics dictate in relaxed graded buffers a fundamental opposition between the defectivity and throughput. For state-of-the-art Si-based applications, the trade-off between defect level and wafer cost (inversely related to throughput) has made the insertion of SiGe graded buffers into production difficult. We aim to mitigate the trade-off by reporting two advances that enable simultaneous improvements in both defectivity and throughput. The first is use of a high growth temperature to allow very fast dislocation glide velocities and growth rates as high as 1.0 μm/min. The second is the use of “pre-threaded” Si substrates, substrates with an elevated density of threading dislocations. By having dislocation nucleation controlled by uniformly distributed substrate threading dislocations, instead of unpredictable heterogeneous sources, impediments to dislocation glide, such as dislocation bundles and pile-ups, are reduced. By incorporating both advances into SiGe graded buffer epitaxy, dislocation pile-up densities are reduced by nearly three orders of magnitude, threading dislocation densities are reduced by a factor of 7.4×, and wafer throughput is increased at least 33%.
Short-period AlGaN based superlattices for deep UV light emitting diodes grown by gas source molecular beam epitaxy
Authors: Nikishin Sergey , Borisov Boris , Kuryatkov Vladimir , Holtz Mark , Temkin Henryk
Published: April 2011

We report the results of two studies of the growth and physical properties of AlGaN-based short-period superlattices (SPSLs), each aimed at improving light emission. In the first experiment, we grow structures on bulk AlN substrates. We observe ∼ 3 times higher luminescence efficiency than identically grown structures on sapphire. In the second experiment, we grow structures on sapphire while controlling the growth mode. We observe a significant improvement in the room temperature cathodoluminescence efficiency (at least by factor of 10) of AlGaN quantum wells when the 3D growth mode is induced by reduced flux of ammonia over identically prepared structures grown in the 2D mode.
Stress and Microstructure Evolution in Compositionally Graded Al1-xGaxN Buffer Layers for GaN Growth on Si
Authors: Weng Xiaojun , Raghavan Srinivasan , Dickey Elizabeth C , Redwing Joan M
Published: April 2011

We have studied the evolution of stress and microstructure of compositionally graded Al1-xGaxN (0 ≤ x ≤1) buffer layers on (111) Si substrates with varying thicknesses. In-situ stress measurements reveal a tensile-to-compressive stress transition that occurs near the half-thickness in each buffer layer. Cross-sectional transmission electron microscopy (TEM) shows a significant reduction in threading dislocation (TD) density in the top half of the buffer layer, suggesting that the compressive stress enhances the threading dislocation annihilation. The composition of the buffer layers varies linearly with thickness, as determined by X-ray energy dispersive spectrometry (XEDS). The composition grading-induced compressive stress offsets the tensile stress introduced by microstructure evolution, thus yielding a tensile-to-compressive stress transition at x ≈ 0.5.
Scanning Tunneling Microscopy Study of Cr-doped GaN Surface Grown by RF Plasma Molecular Beam Epitaxy
Authors: Haider Muhammad B. , Yang Rong , Al-Brithen Hamad , Constantin Costel , Smith Arthur R. , Caruntu Gabriel , O'Connor Charles J
Published: April 2011

Cr doped GaN was grown by rf N-plasma molecular beam epitaxy on sapphire(0001) at a sample temperature of 700 °C. Cr/Ga flux ratio was set to a value from 5% to 20%. Subsequently, scanning tunneling microscopy was performed on these surfaces. Cr incorporates on the GaN surface at 700 °C at a Cr concentration of 5% and less. By increasing the Cr/Ga flux ratio to 20% in CrGaN, linear nano structures were formed on the surface, which were not observed on the bare GaN surface. The RHEED and STM studies reveal that Cr atoms form 3×3 reconstruction when 0.1 ML of Cr was deposited at room temperature on 1×1 adlayer of Ga on GaN(000-1). Cr substitutes Ga on the surface when deposited at 700 °C on the MBE grown GaN(000-1) surface for all the experiments which we have performed provided the Cr concentration is low (∼5%).
High Power AlGaN/GaN Schottky Barrier Diode with 1000 V Operation
Authors: Yoshida Seikoh , Ikeda Nariaki , Li Jiang , Wada Takahiro , Kambayashi Hiroshi , Takehara Hironari
Published: April 2011

We investigated an AlGaN/GaN Schottky barrier diode (SBD) with a field plate structure for a high breakdown voltage. The AlGaN/GaN heterostructure was grown by MOCVD. The AlGaN buffer was grown on the Si (111) substrate and Al0.25Ga0.75N (25 nm)/ GaN (1000 nm) was grown on the buffer layer. The AlGaN/GaN heterostructure without any crack was obtained. After that, a Schottky barrier diode was fabricated using an AlGaN/GaN heterostructure. In order to obtain a high breakdown voltage, a gate field plate structure was used. SiO2 was formed on the AlGaN layer using a plasma chemical vapor deposition. The Schottky electrode of Ni/Au was partially deposited on the SiO2 film towards the ohmic region. The length of field plate structure was also changed to investigate the effect. Ti/Al-silicide was used for an ohmic electrode of SBD. The contact resistance of ohmic electrodes was 8E-6 ohmcm2.

The current-voltage characteristics of an AlGaN/GaN SBD were measured. The reverse breakdown voltage of the diode was also over 1000 V and the reverse leakage current was below 1.5E-6 A/mm.
Influence of Nitrogen Species on InN Grown by PAMBE
Authors: Anderson P. A. , Kinsey R. J. , Kendrick C. E. , Farrel I. , Carder D. , Reeves R. J. , Durbin S. M.
Published: April 2011

Active nitrogen species produced by an Oxford Applied Research HD-25 plasma source have been monitored by optical emission spectroscopy and quadrapole mass spectroscopy. Both techniques confirmed that at higher RF powers and lower flow rates the efficiency of atomic nitrogen production increased; emission spectroscopy confirmed that this was at the expense of active molecular nitrogen (N2*). InN films grown on (0001) sapphire/GaN with higher relative molecular content were found to have lower carrier concentrations than the corresponding films grown with higher atomic content. However, electrical properties of films grown on (111) YSZ showed insensitivity to the active nitrogen content. Etching experiments revealed that films grown on sapphire/GaN were nitrogen-polar, while films grown on YSZ were In-polar, suggesting that film polarity can greatly influence the effect active species have on growth. Lattice relaxation, as measured by reflection high-energy electron diffraction, revealed that the N-polar films grown under high relative molecular flux relaxed fully after ∼60 nm of growth, while the corresponding In-polar film relaxed fully within the first several nm of growth.
Carrier Recombination, Relaxation, and Transport Dynamics in InN
Authors: Chen Fei , Cartwright Alexander N , Lu Hai , Schaff William J
Published: April 2011

Knowledge of the carrier recombination, relaxation, and transport processes in InN materials is essential for determining the applicability of this material system in photonic and electronic applications. In this article, we provide a review of time-resolved spectroscopy experimental techniques and our recent results using these techniques to measure transient processes in InN. Specifically, subpicosecond differential transmission experiments were used to determine the carrier recombination lifetime and the carrier thermalization time of InN. In those experiments, we observed a fast initial hot carrier cooling followed by a slower recombination process. At short times after pulsed excitation, modeling of the observed relaxation suggests that the dominant energy relaxation process is longitudinal optical phonon scattering modified by a strong hot phonon effect at room temperature. An inverse proportionality between the carrier lifetime and the free electron concentration was found. This suggests that donor-like defects or impurities may stimulate the formation of non-radiative recombination centers. Furthermore, we report the measurements of in-plane carrier transport and hole mobility of an InN epilayer by time-resolved transient grating spectroscopy using subpicosecond pulses at 800 nm and ∼1900 nm for grating writing and probing, respectively. The ambipolar diffusion coefficient Da = 2.0 cm2/s and hole mobility µh = 39 cm2/Vs at 300 K near the InN surface were determined by monitoring the transient grating kinetics at various grating periods.
Electron Transport Properties of InN
Authors: Jones Rebecca E. , van Genuchten Henricus C. M. , Li Sonny X. , Hsu Leon , Yu Kin Man , Walukiewicz Wladek , Ager III Joel W. , Haller Eugene E. , Lu Hai , Schaff William J.
Published: April 2011

High-energy particle irradiation has been used to control the free electron concentration and electron mobility in InN by introducing native point defects that act as donors. A direct comparison between theoretical calculations and the experimental electron mobility suggests that scattering by triply-charged donor defects limits the mobility in irradiated samples across the entire range of electron concentrations studied. Thermal annealing of irradiated films in the temperature range 425°C to 475°C results in large increases in the electron mobility that approach the values predicted for singly-ionized donor defect scattering. It is suggested that the radiation-induced donor defects are stable, singly-charged nitrogen vacancies, and triply-charged, relaxed indium vacancy complexes that are removed by the annealing.
Fe-Centers in GaN as Candidates for Spintronics Applications
Authors: Malguth Enno , Hoffmann Axel , Phillips Matthew , Gehlhoff Wolfgang
Published: April 2011

The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 500 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1017 to 2×1020 was studied by means of photoluminescence, photoluminescence excitation (PLE) and Fourier transform infrared (FTIR) transmission experiments. The Fe3+/2+ charge transfer (CT) level was determined to be at 2.86 ± 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 ± 0.10 eV. A bound state of the form (Fe2+, hVB) with a binding energy of 50 ± 10 meV has been established as an excited state of Fe3+. FTIR transmission measurements revealed an internal (5E-5T2) transition of Fe2+ around 400 eV which, until now, was believed to be degenerate with the conduction band. Consequently, a second CT band was detected in PLE spectra.
Characterization of a-plane AlGaN/GaN heterostructure grown on r-plane sapphire substrate
Authors: Iwaya Motoaki , Okadome Yoshizane , Tsuchiya Yosuke , Iida Daisuke , Miura Aya , Furukawa Hiroko , Honshio Akira , Miyake Yasuto , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu
Published: April 2011

The anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction analysis of the heterostructure of AlGaN and GaN grown on r-plane sapphire. The AlGaN layer with a low AlN molar fraction or small thickness is coherently grown on the GaN layer both along the m-axis and c-axis. An increase in AlN molar fraction or thickness in AlGaN, results in a slight relaxation of AlGaN only in one direction due to tensile stress along the c-axis, which is caused by the underlying GaN layer during the growth. The cause of the relaxation of AlGaN in one direction is thought to be a large anisotropically biaxial stress.