bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical and Thermal Stability of Fluorinated Amorphous Carbon Films for Interlayer Dielectric Applications
Authors: Chang J. P. , Krautter H. W. , Zhu W. , Opila R. L. , Pai C. S.
Published: April 2011

The thermal and chemical stability of low k fluorinated amorphous carbon (a-C:F) material, deposited by a novel co-sputtering process using both polytetrafluoroethylene (PTFE) and graphite targets was investigated. Thin films of a-C:F with fluorine concentration of 2–55% were deposited, and carbon is observed by XPS in four distinct chemical states, C-C, C-F, C-F2, C-F 3. The relative intensity of C-Fx to C-C increased in intensity with increasing fluorine content and decreasing deposition temperature. Formation of tantalum fluoride was observed upon deposition of tantalum nitride, and the defluorination of the film could lead to reliability and delamination problems.
Wave Polymerization During Vapor Deposition of Porous Parylene-N Dielectric Films
Authors: Erjavec James , Sikita John , Beaudoin Stephen P. , Raupp Gregory B.
Published: April 2011

Parylene-N films vapor deposited near liquid nitrogen temperature (77 K) undergo a unique ‘wave’ polymerization process in which a rapidly moving reaction front is apparent as the film changes from translucent to optically opaque. This moving reaction front produces a highly porous polymer film. The porosity of these films is approximately 80%. By capturing the wave process on video we have quantified the moving ‘wave’ velocity, which averages 11 cm/s. Timeaveraged deposition rates of the resulting opaque, porous films are more than 8 μm/min. This rate is more than two orders of magnitude greater than the measured deposition rates of nonporous films that are deposited at higher temperatures, at otherwise fixed conditions of monomer delivery rate and deposition chamber pressure.
Effect of Film Thickness and Cure Temperature on the Mechanical Properties of FOx® Flowable Oxide Thin Films
Authors: Liou Huey-Chiang , Pretzer John
Published: April 2011

The mechanical properties and thermal stresses of FOx thin films at different thickness and cured at different temperatures have been investigated by a nanoindentor and a profilometer. In this study, the correlation between structure change, thickness, Si-H/Si-O ratio, modulus, hardness, and calculated coefficient of thermal expansion (CTE) of FOx films have been established. The results show that the modulus of 400°C cured FOx film decreases with increasing film thickness while the hardness slightly varies with increasing film thickness. The calculated CTE of FOx film increases with increasing film thickness. In addition, both the modulus and hardness of FOx films increase with increasing curing temperature. However, the calculated CTE of FOx film decreases with increasing curing temperature. The Si-H/Si-O ratio increases with increasing film thickness but decreases with increasing curing temperature. These results indicate that the increase in modulus and hardness and the decreases in CTE for FOx films are either due to the remaining of Si-H bonds in FOx film at different film thickness or the conversion of Si-H into Si-O when forming the network structure in the FOx film at higher curing temperatures.
Processing and Characterization of Silica Xerogel Films for Low-K Dielectric Applications
Authors: Jain Anurag , Rogojevic Svetlana , Nitta Satya V. , Pisupatti Venumadhav , Gill William N. , Wayner Peter C. , Plawsky Joel L. , Standaert T. E. F. M. , Oehrlein G. S.
Published: April 2011

Surface modified silica xerogel films of high porosity (60 - 90 %) and uniform thickness (0.4–2 μm) were fabricated at ambient pressure on silicon and silicon dioxide. The rheological properties that govern film uniformity were determined. A relation between the final dried film thickness and spin speed was developed. The porosity and thickness of the films could be controlled independently. The same porosity could be obtained over a wide range of aging time and temperature combinations. Fracture toughness was measured using the edge-lift-off technique. The best values were comparable to concrete. Surface modification was affected by treating the film with trimethylcholorosilane (TMCS) and other modifiers. Moisture adsorption was studied at 100% RH using a quartz crystal microbalance technique. Depending upon the degree and kind of surface treatment, films absorbed as much as 32% or as little as 2% of their weight in water. Dielectric constants (K), losses and breakdown strengths were comparable to values for calcined, bulk aerogels. Thin (≤ 500 Å) films of Copper (Cu) and Tantalum (Ta) were deposited on xerogel films and subjected to thermal annealing. No diffusion was observed within the limits of RBS. High-density plasma etching showed that the films etch an order of magnitude faster than conventional SiO2 films.
Morphological Transitions in Fluorinated and Non-Fluorinated Parylenes
Authors: Morgen Michael , Zhao Jie-Hua , Rhee Seung-Hyun , Ryant E. Todd , Ho Huei-Min , Plano Mary Anne , Ho Paul S.
Published: April 2011

A study of temperature-induced crystallinity changes in fluorinated and nonfluorinated parylene thin films using differential scanning calorimetry, thermal stress and wide angle x-ray diffraction measurements is presented. The nonfluorinated parylene (ppx-N) is shown to undergo two phase transitions between 200°C and 300°C. Both transitions show at least some degree of reversibility. The high temperature (β1-β2) transition is accompanied by a sudden shift in stress, which is attributed to a contraction of the polymers chains. A single, reversible phase transition, occurring between 360°C and 400°C, is observed for fluorinated parylene (ppx-F). This transition is likewise marked by a significant shift in stress, and is apparently due to a similar chain contraction.
Morphological transition of Ge islands on Si(001) grown by LPCVD
Authors: Goryll M. , Vescan L. , Lüth H.
Published: April 2011

Hut- and dome-shaped islands have been observed during low-pressure vapour phase epitaxy (LPVPE) of Ge on Si(001) at 700°C. The experiments show that a coarsening process occurs in connection with the deposition process, leading to an island height increase with increasing deposition time (total Ge-coverage was kept constant). The shape transition from huts to domes, which takes place after hut clusters have reached a baselength of 80nm, indicates that huts are not a stable configuration. Photoluminescence measurements show a linear correlation between hut cluster density and integrated photoluminescence intensity.
Self-Assembling of Epitaxial Nisi2 In Si(001)
Authors: Teichert S. , Falke M. , Beddies G. , Hinneberg H.-J.
Published: April 2011

The preparation of buried epitaxial layers of a compound ABx in a matrix of the material A can be performed by allotaxy [1]. In the first process step a distribution of ABx precipitates is prepared in the matrix A by codeposition of A and B. This contribution reports on the spatial distribution and the crystallographic orientation of NiSi2precipitates in the Si- matrix. Cross-section transmission electron microscopy was utilized to characterize the samples. The observed depth distribution of Ni in the Si matrix differs remarkably from the calculated distribution given by the deposition rates of Si and Ni. This redistribution of Ni results in two well distinguishable bands of NiSi2precipitates - a narrow one and a broad one - in the Si matrix. The narrow band consists of epitaxial NiSi2 precipitates; and a mixture of epitaxially and twinned grown NiSi2precipitates is formed in the broad band. Under certain deposition conditions self-ordering of the NiSi2precipitates in the narrow band has been observed parallel and perpendicular to the growth direction. In these cases the diameter of the epitaxial NiSi2precipitates varies between 12 and 50 A and the distance between them is in the order of some 10 Å.
Effects of hydrogen in AlAs growth by atomic hydrogenassisted molecular beam epitaxy
Authors: Jang Kee-Youn , Okada Yoshitaka , Kawabe Mitsuo
Published: April 2011

The transition temperature Tc for the AlAs growth to change from/to a nucleation mode and step-flow mode have been studied on vicinal GaAs substrates (A-surface and B-surface) in molecular beam epitaxy (MBE) and atomic hydrogen-assisted MBE (H-MBE) using reflection high-energy electron diffraction (RHEED). The lowering of Tc was clearly observed in H-MBE compared to conventional MBE. For growth of AlAs on vicinal GaAs substrate in H-MBE, atomic H is thought to promote not only the re-evaporation of Al adatoms on the terrace, but also the incorporation of Al at the step edges, thereby facilitating a step-flow growth mode at a lower temperature than in MBE. The differences in the fundamental growth mode between on A-surface and B-surface have also been studies based on the differences in the atomic structure between the two substrates.
Low-Temperature Si (111) Homoepitaxy and Doping Mediated by a Monolayer of Pb
Authors: Dubon O.D. , Evans P.G. , Chervinsky J.F. , Spaepen F. , Aziz M.J. , Golovchenko J.A.
Published: April 2011

The codeposition of Pb during Si (111) molecular beam homoepitaxy leads to high-quality crystalline films at temperatures for which films deposited on bare Si (111) are amorphous. Like other growth mediating elements-- commonly called surfactants-- Pb segregates to the film surface. Ion channeling and transmission electron microscopy reveal nearly defect-free epitaxy for a Pb coverage of one monolayer and temperatures as low as 310 °C. We have deposited films up to 1000 Å in thickness with no indication that this is an upper limit for high-quality epitaxy. However, a decrease in the Pb coverage during growth by only one tenth of a monolayer leads to highly defective films at these temperatures. The codeposition of both As and Pb results in a striking enhancement of the film quality as well. In this case, while the Pb again segregates to the film surface, the As is incorporated into the film with no apparent segregation. Lead-mediated Si epitaxy on As-terminated Si (111) produces high-quality films in which the As remains buried at the substrate-film interface. These results show Pb-mediated Si (111) homoepitaxy to be a promising strategy for the synthesis of layered structures having abrupt nanoscale dopant profiles
Self-Limited GaAs Wire Growth by Movpe and Application to InAs Quantum Dot Array
Authors: Aritsuka Yuuki , Umeda Tetsuhito , Motohisa Junichi , Fukui Takashi
Published: April 2011

We investigate the growth mode and the growth mechanisms of selectively grown GaAs nanometer wire structures by metalorganic vapor phase epitaxy (MOVPE). The nanometer wire structures with (111)A or (111)B facet sidewalls are grown on SiNx masked (001) GaAs with line and space pattern openings. As the growth proceeds, the growth rates increase because Ga atoms migrate from SiNx mask surface and (111) facet sidewalls. After the wire formation with triangular cross section is complete, no further growth occurs on the top of the wires, which is called self-limited growth mode. The shape and width of the top area are observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM), and the mechanism of self-limited growth is discussed

We also simulate the growth rate during selective area growth. From the comparison with the experimental results and the simulation, we estimate the amounts of Ga atom migration from SiNx mask area and (111) facet sidewalls to the wire areas.

Finally, we form InAs quantum dots on these GaAs wires, and observe photoluminescence spectra from QDs.
Recent Progress in SiC Microwave MESFETs
Authors: Allen S. T. , Sheppard S. T. , Pribble W. L. , Sadler R. A. , Alcorn T. S. , Ring Z. , Palmour J. W.
Published: April 2011

SiC MESFET's have shown an RF power density of 4.6 W/mm at 3.5 GHz and a power added efficiency of 60% with 3 W/mm at 800 MHz, demonstrating that SiC devices are capable of very high power densities and high efficiencies. Single devices with 48 mm of gate periphery were mounted in a hybrid circuit and achieved a maximum RF power of 80 watts CW at 3.1 GHz with 38% PAE.
Properties of 4H-SiC by Sublimation Close Space Technique
Authors: Nishino S. , Matsumoto K. , Chen Y. , Nishio Y.
Published: April 2011

SiC is suitable for power devices but high quality SiC epitaxial layers having a high breakdown voltage are needed and thick epilayer is indispensable. In this study, CST method (Close Space Technique) was used to rapidly grow thick epitaxial layers. Source material used was 3C-SiC polycrystalline plate of high purity while 4H-SiC(0001) crystals inclined 8° off toward <1120> was used for the substrate. Quality of the epilayer was influenced significantly by pressure during growth and polarity of the substrate. A p-type conduction was obtained by changing the size of p-type source material. The carrier concentration of epilayer decreased when a lower pressure was employed. Schottky diode was also fabricated.
The comparative studies of chemical vapor deposition grown epitaxial layers and of sublimation sandwich method grown 4H-SiC samples
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: April 2011

Thermal admittance spectroscopy was used to characterize the shallow dopants in chemical vapor deposition ( CVD) grown thin films and in sublimation sandwich method ( SSM) grown 4H-SiC layers. The values of the activation energy levels of EC − 0.054 eV for Nitrogen at the hexagonal site and of EC − 0.10 eV for Nitrogen at the cubic site were indices of comparison. The net carrier concentrations ( ND − NV ) of the films were determined by capacitance-voltage measurements. The net carrier concentrations for the SSM films ranged from 2 × 1017 to 7 × 1017 cm−3. The two Nitrogen levels were observed in the CVD films. Hopping conduction with an activation energy of EC −0.0058 eV was observed in one SSM sample having ND − NV = 7 × 1017 cm−3.
Impurity Effects in the Growth of 4H-SiC Crystals by Physical Vapor Transport
Authors: Balakrishna V. , Augustine G. , Hopkins R. H.
Published: April 2011

SiC is an important wide bandgap semiconductor material for high temperature and high power electronic device applications. Purity improvements in the growth environment has resulted in a two-fold benefit during growth: (a) minimized inconsistencies in the background doping resulting in high resistivity (>5000 ohm-cm) wafer yield increase from 10–15% to 70-85%, and (b) decrease in micropipe formation. Growth parameters play an important role in determining the perfection and properties of the SiC crystals, and are extremely critical in the growth of large diameter crystals. Several aspects of growth are vital in obtaining highly perfect, large diameter crystals, such as: (i) optimized furnace design, (ii) high purity growth environment, and (iii) carefully controlled growth conditions. Although significant reduction in micropipe density has been achieved by improvements in the growth process, more stringent device requirements mandate further reduction in the defect density. In-depth understanding of the mechanisms of micropipe formation is essential in order to devise approaches to eliminate them. Experiments have been performed to understand the role of growth conditions and ambient purity on crystal perfection by intentionally introducing arrays of impurity sites on one half of the growth surface. Results clearly suggest that presence of impurities or second phase inclusions during start or during growth can result in the nucleation of micropipes. Insights obtained from these studies were instrumental in the growth of ultra-low micropipe density (less than 2 micropipes cm−2 ) in 1.5 inch diameter boules.
Synchrotron X-ray Topography Studies of Epitaxial Lateral Overgrowth of GaN on Sapphire
Authors: Mcnally Patrick J. , Tuomi T. , Rantamaki R. , Jacobs K. , Considine L. , O'hare M. , Lowney D. , Danilewsky A. N.
Published: April 2011

Synchrotron white beam x-ray topography techniques, in section and large-area transmission modes, have been applied to the evaluation of ELOG GaN on A12O3. Using the openings in 100 nm thick SiO2 windows, a new GaN growth took place, which resulted in typical overgrowth thicknesses of 6.8 μm. Measurements on the recorded Laue patterns indicate that the misorientation of GaN with respect to the sapphire substrate (excluding a 30° rotation between them) varies considerably along various crystalline directions, reaching a maximum of a ∼0.66° rotation of the (0001) plane about the [01•1] axis. This is ∼3% smaller than the misorientation measured in the non-ELOG reference, which reached a maximum of 0.68°. This misorientation varies measurably as the stripe or window dimensions are changed. The quality of the ELOG epilayers is improved when compared to the non- ELOG samples, though some local deviations from lattice coherence were observed. Long range and large-scale (order of 100 μm long) strain structures were observed in all multi quantum well epilayers.
Investigation of the Morphology of AlN Films Grown on Sapphire by MOCVD Using Transmission Electron Microscopy
Authors: Samey W. L. , Salamanca-Ribal L. , Zhou P. , Wilson S. , Spencer M. G. , Jones K. A.
Published: April 2011

To determine the effect of growth conditions on AlN film morphology, we investigated several AlN films grown on sapphire by MOCVD with various V/III ratios. Transmission electron microscopy was used to characterize the film's crystalline quality and defect morphology. TEM results show that the resulting film morphology depends on the V/III ratio. Films grown with NH3 flow rates below 170 sccm have high crystalline quality. In contrast, we observe columnar growth and secondary interfaces in films grown with NH3 flow rates at or above 170 sccm. The secondary interfaces are likely to be inversion domain boundaries (IDBs) and may be associated with strain relaxation. We discuss the V/III ratio's effect on crystalline quality, surface roughness, and IDB and columnar structure formation.
Temperature Dependent Morphology Transition of GaN Films
Authors: Zauner A. R. A. , Theue F. K. De , Hageman P. R. , Van W. J. P. , Schermer J. J. , Larsen P. K.
Published: April 2011

The temperature dependence of the surface morphology of GaN epilayers was studied with AFM. The layers were grown by low pressure MOCVD on (0001) sapphire substrates in the temperature range of 980°C-1085°C. In this range the (0001) and {1101} faces completely determine the morphology of 1.5 μm thick Ga-faced GaN films. For specimens grown at 20 mbar and temperatures below 1035°C the {1101} faces dominate the surface, which results in matt-white layers. At higher growth temperatures the morphology is completely determined by (0001) faces, which lead to smooth and transparent samples. For growth at 50 mbar, this transition takes place between 1000°C and 1015°C. It is shown that the morphology of the films can be described using a parameter αGaN, which is proportional to the relative growth rates of the (0001) and the {1101} faces.
Atomic Scale Analysis of InGaN Multi-Quantum Wells
Authors: Benamara M. , Liliental-Weber Z. , Swider W. , Washburn J. , Dupuis R. D. , Grudowski P. A. , Eiting C. J. , Yang J. W. , Khan M. A.
Published: April 2011

InGaN multiquantum wells grown by MOCVD on GaN have been investigated by transmission electron microscopy techniques and numerical analysis of high resolution (HREM) images. One objective of this research was to correlate the atomic structure and emission mechanisms of InGaN quantum well. The studied layers contained 13% or 20% In. It was shown that GaN/InGaN interfaces are rather rough and exhibit an oscillating contrast. Structural defects were found on these interfaces. The relative c-lattice parameter variation in the well was determined using numerical processing of HREM images. The lattice spacings appear to be larger than that expected from Vegard's law suggesting the presence of a biaxial strain. Further observations also revealed a redistribution of In within the well. Instead of a continous In-rich layer, quantum dots were often observed along the well with a regular spacing. The formation of these In-rich dots was not intented and their presence suggests either a periodic modulation of strain along the well or In-rich cluster formation.
Deformation-Induced Dislocations in 4H-SiC and GaN
Authors: Hong M. H. , Samant A. V. , Orlov V. , Farber B. , Kisielowski C. , Pirouz P.
Published: April 2011

Bulk single crystals of 4H-SiC have been deformed in compression in the temperature range 550–1300°C, whereas a GaN thin film grown on a (0001) sapphire substrate was deformed by Vickers indentation in the temperature range 25–800°C. The TEM observations of the deformed crystals indicate that deformation-induced dislocations in 4H-SiC all lie on the (0001) basal plane but depending on the deformation temperature, are one of two types. The dislocations induced by deformation at temperatures above ∼1 100°C are complete, with a Burgers vector, b, of but are all dissociated into two partials bounding a ribbon of stacking fault. On the other 3 hand, the dislocations induced by deformation in the temperature range 550<T<∼ 1100°C were predominantly single leading partials each dragging a stacking fault behind them. From the width of dissociated dislocations in the high-temperature deformed crystals, the stacking fault energy of 4H-SiC has been estimated to be 14.7±2.5 mJ/m2. Vickers indentations of the [0001]-oriented GaN film produced a dense array of dislocations along the three 〈1120〉 directions at all temperatures. The dislocations were slightly curved with their curvature increasing as the deformation temperature increased. Most of these dislocations were found to have a screw nature with their b parallel to 〈1120〉. Also, within the resolution of the weak-beam method, they were not found to be dissociated. Tilting experiment show that these dislocations lie on the {1100} prism plane rather than the easier (0001) glide plane.
Nondegenerate Optical Pump-Probe Spectroscopy of Highly Excited Group III Nitrides
Authors: Schmidt T. J. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P. , Yang Wei
Published: April 2011

We report the results of nondegenerate optical pump-probe absorption experiments performed on GaN and InGaN thin films and quantum wells under the conditions of strong optical band to band excitation. The evolution of the band edge in these materials was monitored as the number of photoexcited free carriers was increased beyond that required to achieve population inversion and observe stimulated emission. The band edge of InGaN is shown to exhibit markedly different high excitation behavior than that of GaN, explaining in part the reduction in stimulated emission threshold that typically accompanies the incorporation of indium into GaN to form InGaN. A comparison of the band edge absorption changes observed in pump-probe experiments to the gain spectra measured in variable-stripe gain experiments is also given.
Comparative Study of GaN Growth Process by MOVPE
Authors: Sun Jingxi , Redwing J. M. , Kuech T. F.
Published: April 2011

A comparative study of two different MOVPE reactors used for GaN growth is presented. Computational fluid dynamics (CFD) was used to determine common gas phase and fluid flow behaviors within these reactors. This paper focuses on the common thermal fluid features of these two MOVPE reactors with different geometries and operating pressures that can grow device-quality GaN-based materials. Our study clearly shows that several growth conditions must be achieved in order to grow high quality GaN materials. The high-temperature gas flow zone must be limited to a very thin flow sheet above the susceptor, while the bulk gas phase temperature must be very low to prevent extensive pre-deposition reactions. These conditions lead to higher growth rates and improved material quality. A certain range of gas flow velocity inside the high-temperature gas flow zone is also required in order to minimize the residence time and improve the growth uniformity. These conditions can be achieved by the use of either a novel reactor structure such as a two-flow approach or by specific flow conditions. The quantitative ranges of flow velocities, gas phase temperature, and residence time required in these reactors to achieve high quality material and uniform growth are given.
IIIB- Nitride Semiconductors for High Temperature Electronic Applications
Authors: Bai X. , Hill D. M. , Kordesch M. E.
Published: April 2011

Thin films of ScN and YN were grown on silicon, quartz and sapphire using metal evaporation and an RF atomic nitrogen source. YN decomposes on contact with water vapor, and only AlN capped films could be stabilized. ScN is stable in air and water, and thin films of this material deposited at temperatures between 300 and 900 °C show a substrate-dependent film texture. Typical growth rates were ∼ 0.1 nm/second with a 300W N discharge at about 0.1 mTorr Nitrogen pressure. Structural characterization by x-ray diffraction, infrared transmission spectroscopy and Hall effect measurements on n-type ScN and the fabrication of p-n junctions of n- type ScN with silicon are presented.
Characterization of GaS-Passivated Quantum-Well Laser Diodes
Authors: Vaughn L. G. , Newell T. C. , Lester L. F. , Macinnes A. N.
Published: April 2011

The degradation of AlGaAs/GaAs diode laser performance during operation is typically due to catastrophic optical damage of the facets caused when thermal runaway occurs. These heating effects are due to the presence of non-radiative recombination sites at and near the facets. MOCVD GaS is deposited on the facets of 825-nm ridge waveguide AlGaAs/GaAs quantumwell laser diodes as an electronic passivation to reduce the number of surface states available for non-radiative recombination. For passivated devices, a peak pulsed power nearly double that of unpassivated devices was achieved. The passivated devices also exhibit a longer lifetime before degradation. The impact of the passivation process on other optical characteristics of the laser diodes will also be discussed.
One-Step Silicon Nitride Passivation by ECR-CVD for Heterostructure Transistors and MIS Devices
Authors: Diniz J. A. , Barros L. E. M. de , Yoshioka R. T. , Lujan G. S. , Danilov I. , Swart J. W.
Published: April 2011

Silicon nitride (SiNx) films with extremely low interface charge densities have been developed by electron cyclotron resonance-chemical vapor deposition (ECR-CVD) deposition on GaAs substrates. The procedure is a one-step process and does not involve H2and/or N2pre-treatment of the sample surface. Characterization by Fourier transform infrared (FTIR) and ellipsometry analysis indicate good properties of the film revealing N-H and Si-N bonds. Results of capacitance-voltage (C–V) measurements show surface charge densities on the order of 5 × 1010cm−2, which we believe is the lowest surface charge density achieved so far over GaAs.
Chemical Vapor Deposited Tungsten Film on Molecular Layer Epitaxially-Grown GaAs and its Application to Low Resistivity Contact
Authors: Oyama Y. , Oshida Y. , Nishizawa J. , Matsumoto F. , Plotka P.
Published: April 2011

W CVD process was caried out on molecular layer epitaxially-grown GaAs just after in-situ surface treatment under optimized AsH3 pressure followed by ex-situ photolithography process. The precursor for W CVD used is W(CO)6. The W/GaAs interface is analyzed using SIMS and RBS/channeling technique. Interface structure was directly observed by cross sectional HRTEM. Plan view HRTEM observation was also carried out. From these physical analyses, it is shown that the mixed layer at W/GaAs interface is estimated to be about 2–3 ML and that the deposited W layer is epitaxially aligned with underlying GaAs lattice. The contact resistance in W/GaAs is obtained by the transmission line measurements (TLM) of patterned W on heavily doped GaAs grown by (molecular layer epitaxy) MLE. The dependence of the contact resistance on the surface treatment prior to the W CVD is also studied. Barrier height of W/GaAs structure is measured by the temperature dependence of I-V characteristics. Contact resistance of non-alloyed structure achieved are 3 × 10−7 Ωcm2 for n-type GaAs:Te and below 5 ×10−8 Ωcm2 for p-type GaAs:C respectively.
Advances in GaAs Mosfet's Using Ga2O3(Gd2O3) as Gate Oxide
Authors: Wang Y. C. , Hong M. , Kuo J. M. , Mannaerts J. P. , Kwo J. , Tsai H. S. , Krajewski J. J. , Weiner J. S. , Chen Y. K. , Cho A. Y.
Published: April 2011

In this article, we review the recent progress on GaAs MOSFET's using in-situ MBE-grown Ga2O3(Gd2O3) as the gate dielectric. Both depletion-mode (D-mode) and inversion-mode (I-mode) GaAs MOSFET's with negligible drain current drift and hysteresis are demostrated. The absence of drain current drift and hysteresis indicates that the excellent stability of the oxide and low oxide/GaAs interface state density have been achieved. The drain current density and transconductance are about one order of magnitude higher than the best previous reported data in the literature for an inversion-mode GaAs MOSFET. Excellent high frequency and power performances were also measured from the depletion-mode devices. These improvements are attributed to the excellent Ga2O3(Ga2O3) oxide properties and novel processing techniques.
Anodic sulfidation and model characterisation of GaAs (100) in (NH4)2 Sx solution
Authors: Elbahnasawy R. F. , Mclnerney J. G. , Ryan P. , Hughes G. , Murtagh M.
Published: April 2011

Electrochemical sulfidation of n-type GaAs (100) has been investigated under anodic conditions with a view to surface passivation for improved electronic and optical properties. This treatment has successfully removed the native oxide and formed a thick layer of gallium and arsenic sulfides displaying high durability against oxidation and optical degradation compared to conventional dipping treatment using (NH4)2S solution. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM) have been used to characterize the treated surfaces. These studies have been used to devise a structural model of the near-surface region. The results of Raman backscattering spectroscopy measurements indicate that there is a 35% reduction of the surface barrier height compared to the untreated surface. This passivation technique has been shown to be effective in reducing surface band bending on GaAs (100) and enhancing the chemical stability of the surface, making it more suitable for electronic and optoelectronic device applications.
High-Density Plasma-Induced Etch Damage of GaN
Authors: Shul R. J. , Zhang L. , Baca A. G. , Willison C. G. , Han J. , Pearton S. J. , Ren F. , Zolper J. C. , Lester L. F.
Published: April 2011

Anisotropic, smooth etching of the group-Ill nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high dc-bias and/or high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional III–V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in sheet resistance and contact resistance for n- and p-type GaN samples exposed to an Ar inductively coupled plasma (ICP). In general, plasma-induced damage was more sensitive to ion bombardment energies as compared to plasma flux. In addition, p-GaN was typically more sensitive to plasma-induced damage as compared to n-GaN.
Kinetics of the Interaction of Atomic Species With (100) Gallium Arsenide Surfaces
Authors: Gheorghita Ligia , Ogryzlo Elmer
Published: April 2011

The interactions of atomic hydrogen, deuterium and sulfur with (100) GaAs surfaces have been studied. The atoms were produced in a remote microwave plasma and their effect on carrier recombination velocities was continuously monitored in situ by the change in photoluminescence intensity (PLI). It was observed that the PLI increased by about 1–2 orders of magnitude following a few seconds exposure to hydrogen and deuterium atoms. A subsequent treatment with sulfur atoms further increased the PLI. A kinetic analysis of the room temperature hydrogen atom interactions with the (100) GaAs surface was attempted. A similar behavior was observed at higher temperatures when hydrogen and deuterium atoms were allowed to interact with a SiSiO2 interface. A comparison of the two systems leads us to conclude that the hydrogen and deuterium atoms can be trapped at interstitial sites near these interfaces. The kinetics of the hydrogen atom loss from these semiconductors is presented and analyzed in terms of a distribution of trapping sites.
Theory of the Sulphur-Passivated InP(001) Surface
Authors: Lewis Laurent J. , Dharma-Wardana Chandré
Published: April 2011

We present a detailed and comprenhensive theoretical investigation of the sulphur-passivated (001) surface of InP. First, the ground-state structure is determined using density-functional methods, including full relaxation of the surface. The lowest-energy structure at 0 K is a striking (2 × 2) reconstruction with the S atoms displaced from the bridge sites to form short and long dimers, belonging to two distinct sublayers. This surface structure is used to calculate the backscattering Raman spectrum; the two peaks arising from surface-layer vibrations predicted by our calculations are observed. Next, our first-principles calculations are extended to the study of a number of other stable states of the surface that can arise upon annealing. For this purpose, we construct and relax several higher-energy states of the surface, and calculate the corresponding core-level photoemission spectra. A remarkable sequence of structures is found to unfold from the fully S-covered ground state as they become energetically accessible. The surface S atoms exchange with bulk P atoms, forming new (and strong) S-P bonds while dissociating pre-existing S–S dimers. The predicted core-level spectra are found to be entirely consistent with the experimental measurements; our calculations indicate that the annealed (at about 700 K) surface is a (2 × 2) structure containing two S and two P atoms per unit cell. Finally, we have used the predicted stable surface structures to calculate the photoemission and inverse photoemission spectra. They are found to agree well with experiment if the surface is assumed to consist of a mixture of the above ground-state and annealed structures.
The (Ga2O3)1−x(Gd2O3)x, Oxides with x = 0–1.0 for GaAs Passivation
Authors: Kwo J. , Hong M. , Kortan A. R. , Murphy D. W. , Mannaerts J. P. , Sergent A. M. , Wang Y. C. , Hsieh K. C.
Published: April 2011

Ga2O3(Gd2O3) film was previously discovered to effectively passivate GaAs surface, and the employment of this oxide as gate dielectric has led to the first demonstration of the enhancement-mode GaAs metal oxide semiconductor field effect transistors (MOSFETs) with inversion. In order to gain insight into the passivation mechanism and elucidate the role of Gd2O3, we have carried out a systematic study of the dependence of the structural and dielectric properties of (Ga2O3)1−x(Gd2O3) on the Gd (x) content. Our studies indicate that it is necessary to have the Gd addition exceeding 14% in order to form an electrically insulating dielectric with low interfacial state density. Furthermore, we found that pure Gd2O3 film grows epitaxially on GaAs in the single domain, (110) oriented Mn2O3 structure. This new crystalline dielectric has a dielectric constant ∼10, and shows excellent dielectric properties with low leakage and high breakdown strength even for films as thin as 2.5 nm. We expect that epitaxial growth of the Mn2O3 structure can be extended to other rare earth oxides, and to other semiconductor substrates like Si.
Selective Oxidation to Form Dielectric Apertures for Low Threshold VCSELs and Microcavity Spontaneous Light Emitters
Authors: Deppe D. G. , Huffaker D. L. , Graham L. A. , Zou Z. , Csutak S.
Published: April 2011

Selective oxidation of AlAs (or AlGaAs) can be used to form buried, low refractive index apertures within high Q Fabry-Perot microcavities. These apertures provide electrical and optical confinement, and for vertical-cavity surface-emitting lasers (VCSELs) have resulted in ultra-low threshold room temperature lasing with threshold currents under 25 μA. When used with quantum dot light emitters, the oxide-apertured microcavity can also be used to control the spontaneous lifetime. We describe the microcavity fabrication based on high Q Fabry-Perot microcavities and selective oxidation, and design and cavity Q constraints for apertured microcavities for quantum well and quantum dot VCSELs and microcavity LEDs. Threshold current densities of quantum well VCSELs are as low as 98 A/cm2, while ground state lasing is also obtained for quantum dot VCSELs. Our initial experiments on microcavities with very small apertures and quantum dot emitters demonstrate up to a factor of 2.3 increase in the spontaneous emission rate.
Chemical Interactions in Ionomers and Ionomer Membranes Containing Metal particles and Ions
Authors: Risen William M.
Published: April 2011

Ionomer membranes are employed in PEM fuel cells as the proton conducting element, but they also hold potential for catalytic applications in both hydrogen based and other low temperature fuel cells. In these applications the reactions of H2, CO, 02, H20 and other small molecules with metal-based catalysts are important to consider. Reactions of these species with perfluorocarbonsulfonic acid based ionomers (PFSA), of which Nafionsa are prototypical, containing Rh, Ru, Pt and other metal ions and particles are shown. Metal carbonyls form with metal ions that have been reduced in situ to reduced valence ions or to metal particles, by the combination of CO and H2O or with H2 directly. Metal nitrogen complexes also can be formed. In addition, the interactions of dissimilar metal ions leads to distinct species with NO or CO, for example, that are different from the products with either ion separately.
Low-Cost Pemfc Development at Siemens - Material Aspects
Authors: Waidhas M. , Datz A. , Gebhardt U. , vhelmolt R. , Hornung R. , Luft G.
Published: April 2011

A state of the art review is given on conceivable concepts of cost reduction for PEM fuel cell systems with specific respect to mobile applications. Achieved results at Siemens are described and will be taken as a basis to assess how close this technology is to the market.
Characterization and Fuel Cell Testing of Radiation-Grafted Psi Membranes
Authors: Brack H.-P. , Koebel M. M. , Tsukada A. , Huslage J. , Buechi F. , Geiger F. , Rota M , Scherer G. G.
Published: April 2011

We have demonstrated earlier the useful performance of our PSI radiation-grafted membranes in terms of the current-voltage characteristics of 30 cm2 active area fuel cells containing these membranes and their long-term testing over 6,000 h at 60 °C. We report here on testing of PSI radiation-grafted membranes in these fuel cells at 80 °C and in short stacks comprised of two or four 100 cm2 active area cells. The in-situ degradation of membranes has been investigated by characterizing membranes both before testing in fuel cells and post-mortem after testing in fuel cells. Characterization was accomplished by means of ion-exchange capacity and infrared and Raman spectroscopic measurements. In addition, a rapid screening method for our ex-situ testing of the oxidative stability of proton-conducting membranes was developed in this work. Comparison of the initial screening test results concerning the oxidative stability of some perfluorinated, partially-fluorinated, and non-fluorinated membranes compare well qualitatively with the relative stability of these same membranes during their long-term testing in fuel cells.
Electrolytic V2O5: Synthesis, Characterization and Lithium Insertion Behavior
Authors: Potiron E. , Salle A. Le Galla , Verbaere A. , Piffard Y , Guyomard D.
Published: April 2011

Electrolytic V2O5 materials were prepared by electrochemical oxidation of vanadyl ions in aqueous solution. The electrodeposition reaction includes two steps: an oxidation into soluble species followed by a precipitation. With the use of various electrodeposition conditions and subsequent heat treatment it is possible to obtain e-V2O5 compounds with different VIV and water contents.

e-V2O5 compounds are mixed valence, hydrated vanadic acids and their formula can be written as H0.4V2O5.2−δ.nH2 with 0.04<8<0.22 and 0<n<1.8. These poorly crystallized layered compounds undergo a phase transformation into α-V2O5 starting at 240°C.

The electrochemical intercalation of lithium into these compounds shows two main single phase phenomena at ≈3.2V/Li and ≈2.6V/Li. Their capacity retention is better than that of other V2O5 reference compounds, but the reversible capacity down to 2V is only ≈100Ah/kg at a rate faster than C/5, due to kinetic limitations.
Investigations of Fe-Cr Ferritic Steels as Sofc Interconnect Material
Authors: Linderoth S. , Larsen P. H.
Published: April 2011

Pure Fe-Cr alloys with a Cr-content between zero and 60 wt% have been investigated with respect to their thermal expansion from room temperature to 1100°C and their corrosion resistance in air and humidified hydrogen up to 1300'C. The thermal expansion coefficient of the ferritic Fe-Cr steels is close to that of the supports used in the manufacture of thin-electrolyte cells. The corrosion resistance in air and humidified hydrogen appears to be best for a Cr content around 20 wt%. In addition, a ceria coating is found to reduce significantly the scale growth. Preliminary results for a Fe78Cr22foil indicates that an electrical contact resistance less than 3 mQcm2can be obtained between the alloy and a Ni/YSZ anode.
Electrochemical Lithium Intercalation into Nb2O5Cathode for 2 V Class-Secondary Lithium Batteries
Authors: Kumagai Naoaki , Komaba Shinichi , Kumagai Nobuko
Published: April 2011

Nb2O5powder was prepared by heating niobium hydroxide in the temperature range from 600 to 1000°C. The crystal system of Nb2O5compounds depended on the heating temperatures,i.e., hexagonal, orthorhombic and monoclinic Nb2O5compounds were obtained at 600, 800 and 1000°C, respectively. Electrochemical lithium intercalation into the three Nb2O compounds was investigated in a cell with an LiClO4-propylene carbonate electrolytic solution for the application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of 2 V class-lithium battery, which will play important role in power supply for IC memory backup developed recently. The thermodynamics and kinetics of the lithium intercalation into the Nb2O5cathode have been investigated. The thermodynamic parameters, such as standard free energies, lithium partial molar entropy, interaction energies between ions, the crystal lattice parameters, and the kinetic parameters, such as chemical and self diffusion constants, have been obtained as a function ofx-value in LiNb2O5.
Preparation and Electrochemical Characterization of LiCoO2 Single Crystal Particles prepared by Super Critical Water Synthesis (SCWS)
Authors: Kanamura Kiyoshi , Umegaki Takao , Toyoshima Katsunori , Okada Ken-ichi , Hakuta Yukiya , Adschiri Masafumi , Arai Kunio
Published: April 2011

LiCoO2 single crystal particles were obtained by super critical water synthesis (SCWS) under optimized preparation conditions. The particle size of the LiCoO2 was less than 1 μm, which was much smaller than that of LiCoO2 prepared by a standard method. However, some unknown crystalline and amorphous phases coexisted with the well defined LiCoO2 single crystal particles. The discharge and charge characteristics of the LiCoO2 prepared by the SCWS were examined by some electrochemical methods. In the first cycle, an irreversible behavior was observed, and then the gradual decrease of the discharge capacity with discharge and charge cycle was also detected. The stable discharge capacity was estimated to be 80 mA h g−1 after the 100th cycle. This result may be due to the existence of amorphous phases and some structural defects.
In-Situ X-Ray Diffraction Studies On Lithium- Ion Battery Cathodes
Authors: Rodriguez Mark A. , Ingersoll David , Doughty Daniel H.
Published: April 2011

LiNi0.8Co0.2O2 and LiNiO2 have been characterized in-situ XRD. LiNi0.8Co0.2O2 does not undergo a monoclinic phase transformation but remains a hexagonal lattice throughout the entire charging cycle. It is hypothesized that Co-doping may help stabilize the hexagonal structure.
Solution-Based Synthesis of Manganese Oxide Cathodes for Lithium Batteries
Authors: Manthiram A. , Kim J. , Choi S.
Published: April 2011

With an objective to overcome the cyclability problems of manganese oxides, solution-based procedures are pursued to synthesize metastable manganese oxides. Reduction of permanganate with lithium iodide in an acetonitrile medium followed by heating at 250 °C in vacuum gives an amorphous lithium sodium manganese oxyiodide that is intimately mixed with crystalline NaIO3. On the other hand, oxidation of manganese acetate with lithium or hydrogen peroxide in presence of lithium hydroxide followed by firing at T < 500 °C gives the metastable spinel oxides, Li4Mn5O12 and Li2Mn4O9-δ. The amorphous manganese oxide exhibits excellent cyclability with a capacity > 275 mAh/g at 4.3-1.5 V. The presence of NaIO3 and a unique microstructure are found to play a critical role in the electrochemical properties. Although Li4Mn5O12 could be achieved without much oxygen vacancies, Li2Mn4O9-δ has significant amount of oxygen vacancies with δ > 0.35. Both Li4Mn5O12 and Li2Mn4O9-δ exhibit capacities around 150 mAh/g with good cyclability in the 3 V region.
Composition-Structure Relations in Organically Modified Silica Gels
Authors: Hüsing Nicola , Schubert Ulrich
Published: April 2011

Monolithic silica aerogels modified by functional organic groups were prepared by basecatalyzed sol-gel processing of Si(OR)4 / R'Si(OMe)3 mixtures (R' = organofunctional group), followed by drying of the wet gels with supercritical CO2. When the functional organic group has only weakly or no basic properties, the microstructure of the obtained aerogels is similar to that of an unmodified silica aerogel prepared under the same conditions and quite independent of the kind of functional group. The experimental findings are explained by a two-stage process in which the R'Si≡ units condense to a pre-formed gel network obtained by hydrolysis and condensation of Si(OR)4. An increasing portion of R'Si(OMe)3 has the same effects on the hydrolysis and condensation reactions as decreasing the bulk density of an unmodified silica aerogel and the same structural consequences as increasing the water / silane ratio and the catalyst concentration acting on Si(OR)4. This leads to larger primary particles and, associated with that, smaller specific surface areas. The two-stage process is not observed when R' contains a strongly basic substituent such as NH2 or NHCH2CH2NH2. The structural parameters indicate that in these cases both R'Si(OMe)3 and Si(OR)4 are involved in the built-up of the gel network. This can be explained by extensive hydrogen bonding between the amino groups and silanol groups.