bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced CVD Diamond Microtip Devices for Extreme Applications
Authors: Patterson D.E. , Jamison K.D. , Kempel M.L. , Freeman S.
Published: April 2011

Extreme Devices has fabricated and tested gated CVD diamond microtip arrays for use as cold cathodes in a variety of high power, high temperature, and high radiation applications. The uses for these devices include direct replacement of hot filament cathodes, microwave amplifiers, spaceborne sensors, and other areas requiring devices that provide high current output and that will function in harsh environments. The basic architecture of the device including an overview of the method for obtaining the self-aligned gated diamond microtip array is presented. Key developments for these robust devices include low electron extraction fields (3 V/μm), high current density output (>75A/cm2), stable operation for long periods of time, and operation in severe (high pressure) conditions. The gated cathodes offer low turn-on voltages (22 V) and appear to be well suited to a number of applications.
Relationship of Field Emission Characteristics on Process Gas Nitrogen Content in Nitrogen Doped Diamond Films
Authors: Sowers A.T. , Ward B.L. , Nemanich R.J.
Published: April 2011

This study explores the field emission properties of nitrogen doped diamond grown by microwave plasma CVD. Several diamond samples were grown on silicon under varying conditions. With certain process parameters, films can be grown which exhibit photoluminescence bands at 1.945eV and 2.154eV that are attributed to single substitutional nitrogen. Field emission characteristics were measured in ultrahigh vacuum with a position variable anode. For samples grown with gas phase [N]/[C] ratios less than 16, damage from micro-arcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured without damage. These measurements indicate relatively high threshold fields (>100V/νm) for electron emission. From the data, two possible field emission mechanisms are presented. Conducting defect states in the bandgap of diamond may provide a source of electrons to the emitting diamond surface.
Ion Beam Techniques for Low K Materials Characterization
Authors: Bakhru H. , Kumar A. , Kaplan T. , Delarosa M. , Fortin J. , Yang G.-R. , Lu T.-M. , Kim S. , Steinbruchel C. , Tang X. , Moore J. A. , Wang B. , McDonald J. , Nitta S. , Pisupatti V. , Jain A. , Wayner P. , Plawsky J. , Gill W. , Jin C.
Published: April 2011

Ion beam analysis techniques have become very useful for characterization of low k materials. Studies on several ion beam analysis techniques will be discussed. Rutherford Backscattering Spectrometry (RBS) provides a very powerful analytical technique for the thickness and porosity measurements on porous Si0 2 films. Nuclear Reaction Analysis (NRA) techniques for hydrogen and fluorine profiling are very useful to characterize fluorinated polymer and fluorinated oxide films. Examples of low k materials including Si02:F, Parylene-AF and Teflon-AF will be discussed. Fluorine diffusion in to metals and various interface effects between metal and low k materials will be presented.
Adhesion Energy Measurements of Multilayer Low-K Dielectric Materials for ULSI Applications
Authors: Shaffer E. O. , Mills M. E. , Hawn D. , Van Gestel M. , Knorr A. , Gundlach H. , Kumar K. , Kaloyeros A. E. , Geer R. E.
Published: April 2011

Currently, the IC industry is researching the integration of a variety of materials to meet the low dielectric constant requirement for improved back-end of line (BEOL) interconnect performance. One critical dimension for successful ntegration of these new materials is maintaining mechanical integrity through multilayer processes. This includes both cohesive and adhesive fracture resistance. The latter adds additional complexity in that adhesive toughness is a function of the adherend materials and the processes used to join them. Hence, many good dielectric materials may be rematurely eliminated from further research not because of inherently poor adhesion but because of the necessity to optimize processing strategies.

In this paper, we use the modified Edge Liftoff Test (m-ELT) to quantify the mechanical adhesion of multilayer blanket coatings. A specific example is used to demonstrate the utility of combining the m-ELT with surface analysis to optimize the reliability of low-K dielectric resins for use in ULSI applications. The system studied consists of a Cyclotene™5021(BCB) low-K material integrated with CVD aluminum for single level, damascene structures. The effects of liner layer metallurgy and surface plasma treatments are measured. Surface analysis is done on the failed parts to understand the location of the failure. In this way recommendations for process optimization can be made.
Study of the thermal properties of polymeric dielectric materials by photothermal technique
Authors: Hu Chuan , Ogawa Ennis T. , Hay Michael F. , Ho Paul S.
Published: April 2011

In this paper, we present some results of the newly developed on-wafer photothermal measurement. To study thermal anisotropy, the out-of-plane thermal diffusivity measured from this technique is compared with the in-plane thermal diffusivity by measured by ISTS [1]. In addition to the thermal properties, the agreement with mechanical [2] and optical properties are also shown. The significance of different thermal performance between low K dielectric medium materials and SiO2 suggests that greater attention should be paid to thermal properties for integrated devices with low K materials.
Dielectric Behavior and Phonon Damping in Low-Dielectric Constant Perovskite Materials
Authors: Katiyar Ram S. , Siny Igor , Guo R. , Bhalla A. S.
Published: April 2011

We have carried out a comparative study of the dielectric losses in some complex perovskites with both 1:1 and 1:2 compositions of the B ions, namely, SrAl1/2Nb1/2O3 (SAN), SrAl1/2Ta1/2O3 (SAT) and BaMg1/3Ta2/3O3 (BMT). The samples were prepared in two forms, viz. ceramics and single-crystal fibers, the latter were grown by laser heated pedestal growth technique (LHPG). All of these materials possess low dielectric constants, low losses and high Q values. In contrast to relaxor ferroelectrics, that as a rule exhibit broad features in their Raman spectra, SAN, SAT and especially BMT have very narrow phonon lines in the Raman spectra. A linear correlation is found between the microwave dielectric losses and the width of first order phonon lines in a sequence of BMT → SAT → SAN ceramics with increasing phonon damping. Moreover, the phonon damping decreases in materials with non-close-packed structure where there is enough space for undisturbed phonon vibrations. The problem of charge compensation in compounds with the Bsite disorder is also discussed.
Novel Technique for Measuring Through-Plane Thermo-Mechanical Properties of Thin Polymer Films
Authors: Patel K. S. , bidstrup-Allen Sue Ann , Kohl P. A. , HODGE T. C.
Published: April 2011

Polymer thin films (less than 20 ltm) are widely used as coatings and inter-level dielectrics in microelectronic applications. In multi-layer structures, stresses generated in the films due to interaction with adjacent layers and solvent evaporation induced shrinkage, cause the polymer chains to orient in the plane of the film resulting in anisotropic film properties. Characterization of properties in all directions is essential for accurate electrical and mechanical design and modeling.

A new technique has been developed to measure, in-situ, the through-plane (z) properties of thin polymer films. A parallel plate capacitor device and an interdigitated electrode structure were used as sensors to detect changes in dielectric constant and thickness of thin polymer films under thermal or mechanical loading. The through-plane compression modulus and coefficient of thermal expansion were calculated and results are reported for benzocyclobutene (BCB) films.
Plasma etching of organic low-dielectric-constant polymers: comparative analysis
Authors: Baklanov M. R. , Vanhaelemeersch S. , Alaerts C. , Maex K.
Published: April 2011

The etch characteristics of the low-k dielectrics DVS BCB (BCB hereafter) and SILK in oxygen/fluorine plasmas are studied. In an O2/NF3 plasma afterglow, the etch rate of both polymers first increase linearly with increasing NF3 concentration, then decreases monotonously. A fluorine plasma afterglow does not etch either BCB nor SILK but strongly changes their chemical and optical properties. Reactive ion etching (RIE) of the polymers shows a different behaviour. The etch rate of SILK in a pure oxygen plasma is maximal, but BCB is etched slowly. The fluorine additives increase the etch rate of BCB. The etch rate of SILK decreases with increasing fluorine concentration. RIE in a pure SF6 plasma shows good etch characteristics and can be used for some practical applications. Mechanisms of the reactions are discussed.
Plasma Etching of Hydrogen-Silsesquioxane
Authors: Liu Youfan , McMillan Chris , Dall Fred
Published: April 2011

CF4 plasma etching of hydrogen-silsesquioxane films on bare silicon substrates was conducted. An increase in average etching rate and a decrease in dielectric constant from 2.9 to 2.7 were observed after a top layer was removed from the surface of the film, indicating that a negative density depth gradient in the film was developed during the cure processing, A small part of the reduction in dielectric constant may be attributed to structural change resulting from the plasma interaction with the films since a small amount of Si-F bonds were identified in the surface layer of the film after plasma etching. There are indications in the x-ray photoelectron spectroscopy (XPS) spectra that traces of fluorocarbon polymer residue have been generated during the plasma etching. The results of this study also indicate a possibility of obtaining a lower dielectric constant HSQ film by plasma etching.
Integration Studies of Plasma Deposited Fluorinated Amorphous Carbon
Authors: Mountsier Thomas W. , Samuels John A. , Swope Richard S.
Published: April 2011

Recently, we reported the deposition of fluorinated amorphous carbon (FlAC) from hexafluorobenzene (C6F6) under parallel plate (PP) and inductively coupled plasma (ICP-HDP) conditions. Based on initial materials testing, these two platforms generated comparable materials with low dielectric constants (2.4 – 2.8), low weight loss/shrinkage (< 1.5 %/hr. at 425° C), hardness (2–3 Gpa) and adhesion (4–9 kpsi). Here we attempt to answer a basic integration question: FIAC compatibility with other materials used in the interconnect scheme. Investigations of adhesion of F1AC to, and capped by, silicon oxide, silicon nitride and various metals shows generally greater stability of the ICP generated material vs. PP-FIAC. Failures appeared to occur primarily at the FIAC/film interface at 400 and 300 °C for ICP and PP respectively. Although thickness-loss and weight-loss measurements indicate good thermal stability, TDS spectra show low-level outgassing of fluorine-based molecules and fragments even in samples annealed for 4 hours at 400 °C, resulting in interface failures. Plasma treatments and anneals of the F1AC were found to have a minimal effect but liner/cap composition and processing has a strong influence on the adhesion of other films to the fluorocarbon.
Liquid-Phase Deposition of Low-K Organic Silicon-Oxide Films
Authors: Usami K. , Sugahara S. , Sumimura K. , Matsumura M.
Published: April 2011

Low-K silica films were grown from the liquid phase using methyl-triethoxy-silane. Physical and chemical properties were investigated together with electronic properties. The film had dense methyl groups and showed insulating characteristics even under as-grown conditions. The dielectric constant, low-field resistivity and breakdown field-strength were 3.6, 1013 Ωcm and IMV/cm, respectively, for the as-grown film. They were improved to 2.6, more than 1015 Ωcm and more than 3MV/cm, respectively, after 300°C vacuum annealing
Electrical Reliability of Cu and Low-K Dielectric Integration
Authors: Wong S. Simon , Loke Alvin L. S. , Wetzel Jeffrey T. , Townsend Paul H. , Vrtis Raymond N. , Zussman Melvin P.
Published: April 2011

The recent demonstrations of manufacturable multilevel Cu metallization have heightened interest to integrate Cu and low-K dielectrics for future integrated circuits. For reliable integration of both materials, Cu may need to be encapsulated by barrier materials since Cu ions (Cu+) might drift through low-K dielectrics to degrade interconnect and device integrity. This paper addresses the use of electrical testing techniques to evaluate the Cu+ drift behavior of low-K polymer dielectrics. Specifically, bias-temperature stress and capacitance-voltage measurements are employed as their high sensitivities are well-suited for examining charge instabilities in dielectrics. Charge instabilities other than Cu+ drift also exist. For example, when low-K polymers come into direct contact with either a metal or Si, interface-related instabilities attributed to electron/hole injection are observed. To overcome these issues, a planar Cu/oxide/polymer/oxide/Si capacitor test structure is developed for Cu+ drift evaluation. Our study shows that Cu+ ions drift readily into poly(arylene ether) and fluorinated polyimide, but much more slowly into benzocyclobutene. A thin nitride cap layer can prevent the penetration.
Polymer/metal Interfaces in Interconnect Structures: Moisture Diffusion and Stress Corrosion Effects
Authors: Ma Qing , Tran Quan , Pan Chuanbin , Fujimoto Harry , Chiang Chien
Published: April 2011

Moisture can cause a host of reliability problems at interfaces including interface debonding. Two mechanisms can be identified. First, moisture at an interface can reduce the interface bonding strength dramatically by altering the chemical bonds. Second, when an interface with a crack or a crack-like defect is under tensile stresses, stress corrosion may allow crack growth at stresses much lower than critical fracture would require. To avoid wet interfaces, wafers should be briefly baked or exposed to a plasmain situbefore the next film deposition step. However, moisture can also reach interfaces by diffusion along interfaces from unprotected edges during a wet process, such as CMP, or during storage in the ambient. In this work, the effect of moisture induced interface strength reduction was utilized to determine the diffusion distance. By using a mechanical peel technique, the diffusivity of moisture along the interface between Al and a poly(arylene ether) based low-K material (PAE2) was measured to be 4–6 μm2/s. Stress corrosion was studied using a special 4-point bend technique so that both strain energy release rate and crack velocity can be obtained. It was found that the mechanism of stress corrosion at this interface is more complicated compared to that in a bulk material: while the chemical reaction took place at the crack tip, moisture diffusion was also occurring along the interface ahead of the crack tip, preconditioning the interface. There appeared to be a region that kinetics was limited by interfacial moisture diffusion and reaction, from which the reaction time for interface weakening was estimated to be ∼ 10 seconds. It was also found that even for samples saturated with moisture, the relative humidity of the test environment was still very important.
Properties Development During Curing of Low Dielectric-Constant Spin-On Glasses
Authors: Cook Robert F. , Liniger Eric G. , Klaus David P. , Simonyi Eva E. , Cohen Stephan A.
Published: April 2011

Variations in the electrical and mechanical properties of silsesquioxane spin-on glass thin films are examined as a function of curing time and temperature. Particular attention is paid to the trade-off between producing low dielectric constant films, suitable for advanced microelectronic interconnection structures, and mechanically stable films, able to withstand semiconductor wafer fabrication processes. Two critical aspects of the mechanical stability of spin-on glasses are shown to be: the positive thermal expansion mismatch with silicon–leading to tensile film stresses; and reactivity with water–leading to susceptibility to stress-corrosion cracking.
Electromigration Study of Ai/Low K Dielectric Line Structures
Authors: Wang P.-H. , Pellerin J. G. , Fox R. J. , Ho P. S.
Published: April 2011

Electromigration reliability is a key concern for implementation of low dielectric constant (k) materials for on-chip interconnects. To address this problem, we have carried out a comparative study of electromigration performance for Al(0.5 wt% Cu) line structures formed with TEOS-based SiO2 and a low k polymeric material, poly(arylene ether) (PAE). The test structures consist of 800 μm long single-level ines. Resistometric measurements were performed to determine electromigration lifetime. To supplement lifetime measurements, TEM was used to measure overall grain size and electron back-scatter diffraction (EBSD) was employed to determine the local grain orientation and grain boundary characteristics in the line structure. In addition, SEM was used to examine void morphology. Microstructural analysis revealed a larger grain size and an enhanced (111) texture in PAE-passivated lines compared to TEOS-passivated lines. The differences can be attributed to a high-emperature process used to cure the PAE dielectric. The overall results obtained in this study show reasonably good electromigration performance for low k dielectric interconnects.
The Response of High Voltage 4H-SiC P-N Junction Diodes to Different Edge Termination Techniques
Authors: Oder T. N. , Tin C. C. , Williams J. R. , Isaacs-Smith T. , Madangarli V. , Sudarshan T. S.
Published: April 2011

Edge termination is an important aspect in the design of high power p-n junction devices. In this paper, we compare the breakdown characteristics of 4H-SiC p+-n diodes with oxide passivation and with edge termination using either low or high energy ion implantations. N- and p-type epilayers of 4H-SiC were grown by chemical vapor deposition on n+ 4H-SiC wafers. Circular mesa structures of different diameters were patterned and isolated by reactive ion etching. Four types of samples were fabricated. The first group was not implanted or passivated and was left for control. The second type consisted of oxide-passivated diode structures while the third and fourth types were ion implanted with 30 keV Ar+ and 2.2 MeV He+ ions, respectively. The time dependent breakdown characteristics were determined using a fast voltage ramp technique. The reverse bias breakdown voltages and leakage currents of these diodes were different for the different types of the edge termination. Diodes terminated using 2.2 MeV ion implantation yielded the best breakdown characteristics. A majority of the diodes exhibited abrupt breakdown.
Carrier relaxation and recombination in InGaN/GaN quantum heterostructures probed with time-resolved cathodoluminescence
Authors: Zhang Xingang , Rich D. H. , Kobayashi J. T. , Kobayashi N. P. , Dapkus P. D.
Published: April 2011

Spatially, spectrally, and temporally resolved cathodoluminescence (CL) techniques have been employed to examine the optical properties and kinetics of carrier relaxation in InGaN/GaN heterostructure and single quantum well (QW) samples. CL images of the QW sample revealed a spotty cellular pattern indicative of local In compositional fluctuations on a scale of < 100 nm. The compositional variations induce local potential fluctuations, resulting in a strong lateral excitonic localization at InN-rich regions in the InGaN QW layer. Time-resolved CL measurements revealed a lateral spatial variation in the luminescence decay time which correlates with the spatial variation in the luminescence efficiency. A reduced lifetime is observed at boundary regions between centers of excitonic localization. A detailed time-resolved CL study shows that carriers generated in the boundary regions will diffuse toward and recombine at the InN-rich centers. An electron beam induced modification of the emission spectra was observed for InGaN/GaN heterostructure samples. Exposure to the e-beam resulted in a shift in the near-band gap emission to higher energies with a simultaneous increase in the emission intensity. These result are interpreted as a modification of the surface passivation through e-beam exposure and carbidization of the surface.
Electrical Stabilization of Diamond Mis Interface and Misfets by Ultrahigh-Vacuum Process
Authors: Yun Young , Maki Tetsuro , Tanaka Hiroyuki , Kobayashi Takeshi
Published: April 2011

In order to obtain electrically stabilized MIS interface, a diamond metal-insulator- semiconductor field-effect transistor (MISFET) was prepared by means of reduced-oxygen process including ultrahigh-vacuum (UHV) process, and its electrical properties were closely investigated. According to the results, observed effective mobility (μeff) was 400 cm2/Vs at room temperature, which is the highest value obtained until now in the diamond FET at room temperature. The transconductance (gm) and surface state density (Nss) of the device operation region was 5mS/mm and ∼ 1010/cm2 eV, respectively, which is also comparable with conventional Si MOSFETs with the same gate length (Lg = 30μm).
Nitridation of Substrates With Hydrazine Cyanurate for The Growth of Gallium Nitride
Authors: Kropewnicki T. J. , Kohl P. A.
Published: April 2011

The use of purified hydrazine cyanurate as a solid source of hydrazine in the low temperature nitridation of GaAs (100) and (111) and sapphire (0001) is demonstrated. Thenitridated surfaces were analyzed by X-ray Photoelectron Spectroscopy (XPS) for chemical composition and Atomic Force Microscopy for surface morphology. The GaAs surfaces were composed primarily of GaN, GaAs, and Ga2O3, and were as smooth as unprocessed standards. The nitridated sapphire surfaces were composed of A1NxO1-x and exhibited three-dimensional growth for long nitridation times.
Studies On The Intermetallic Semiconductor RuAl2
Authors: Ponnambalam V. , Varadaraju U. V.
Published: April 2011

The intermetallic compound RuAl2 with Nowotny chimney-ladder structure is synthesized using arc melting technique. The electrical resistity and thermo electric power measurements were carried out in the temperature range 300–1000K. The resistivity increases with increasing temperature and reaches a maximum value at about 700K. Thermo electric power (TEP) of the sample is negative and the value is about -80 µV/K at RT. The value increases with increasing temperature reaching a maximum value of -140 µV/K at about 600K. The compound exhibits temperature independent power factor in the temperature range 300–550K The calculated figure of merit 1.3 × K-1 is comparable to 7 × 10-4 K-1 of Si-Ge alloys which are used as high temperature thermoelectric materials.
Transient Photoconductivity of GaN Thin Film On Sapphire Substrate
Authors: Chen Z. Z. , Shen B. , Zhang R. , Zhang X. Y. , Yang K. , Chen H. , Chen P. , Zang L. , Zhou Y. G. , Zheng Y. D. , Wu Z. S. , Sun X. T. , Chen F.
Published: April 2011

We studied the transient photoconductivity(PC) properties of GaN thin film on (0001) sapphire substrate. The decay curves of PC obtained by YAG:Nd pulsed laser are divided into two special regions, which are the beginning and tail decay regions, corresponding to two time constants, 0.1 ms and 1.0 ms, respectively. Keeping the same light intensity and bias voltage, when the sample was heated to 300°C, the time constants are both reduced. It shows that there are a large number of traps at the position of tens of meV above the valence band edge. The PC ascends S-shaped when the data were collected during the first 200 ns. As the sample is not shined, the PC sharply reduces and oscillates, indicating that the carriers redistributed between the deep traps and the valence band. The experiment results are explained by the model that involves two hole trapping levels, the shallow trapping level and the deep trapping level. Moreover, the mechanism of the curves varied as the light intensities are also explained by the model.
Incorporation Of Er Into GaN By in-situ Doping During Halide Vapor Phase Epitaxy
Authors: Zhang Rong , Kuech T. F.
Published: April 2011

The incorporation of Er into GaN by in-situ doping during halide vapor phase epitaxy has been investigated. The NH3, HCl, metallic Ga and Er were used as source materials, while N2 was employed as a carrier gas. The GaN:Er films were obtained at different Ga/Er source temperatures. The SIMS analysis shows that the steady state Er doping concentration can be as high as 2×1018 cm−3. All in-situ Er-doped samples luminescence at 1.54 μm due to the 4I13/2 → 4I15/2 transition of Er3+ at both low (11K) and room temperature. The higher the Ga/Er boat temperature, the stronger the 1.54 μm luminescence, implying a higher incorporation rate of Er into the GaN. The 4I11/2 → 4I15/2 transition luminescence, centered around 980 nm, can also be detected at both low and room temperature. The broad-spectrum PL measurements exhibited sharp bandedge luminescence without the presence of the yellow luminescence band.
The Effect of Thermal Annealing of Au Contacts on 6h-Sic and 4h-Sic
Authors: Shi D. T. , Lu W. , Chen H. , Collins W. E.
Published: April 2011

The annealing effects of gold contacts on SiC single crystal substrates have been investigated using SPM and XPS/AES. Ultra-thin Au films with thicknesses of 30 Å and 150 Å, respectively, were fabricated onto both 4H- and 6H-SiC substrates via rf sputtering. The Au/SiC systems were then undergone a series of annealing with temperatures ranging from 200 °C to 400 °C. This study reveals that the sputtering system can generally produce a thin film of uniformly distributed nano-meter sized granular particles. The size of the particles increases with both the thickness of the ultra-thin film and annealing temperature. The thicker Au film revealed pin-hole damages after 300 °C annealing and severe cracking and spalling after 400 °C. However, the thinner Au film only demonstrated the increase of particle sizes. The atomic ratio of gold to silicon in the surface region decreases with the increase of annealing temperature, which indicates the diffusion of gold into silicon carbide. No significant changes of the Schottky barrier heights have been found for Au contacts onto both 6H- and 4H-SiC in the annealing temperature range. After the 400 °C annealing, a noticeable SiO2/SiOx, peak was unveiled in the XPS spectra.
X-Ray Photoemission Spectromicroscopy Of Gan And AIGan
Authors: Lorusso G. F. , Solak H. , Cerrina F. , Underwood J. H. , Batson P. J. , Kim Y. , Cho Y. , Kisielowski C. , Krueger J. , Weber E. R.
Published: April 2011

We investigate here for the first time GaN and AIGaN films by using x-ray photoemission spectromicroscopy. As compared to conventional x-ray photoemission spectroscopy (XPS), spectromicroscopy can provide spatially resolved information on the chemical composition of the sample surface. The experimental results where obtained by using MAXIMUM, a scanning photoemission microscope installed on 12.0 undulator beamline at the Advanced Light Source (ALS), Berkelely, allowing for a spatial resolution of 100 nm. We investigate here GaN and AlGaN thin films grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The results clearly indicate the great potential of spectromicroscopy in investigating chemical inhomogeneity, inpurities and localization in GaN and AlGaN thin films.
High-pressure investigation of InGan quantum wells.
Authors: Perlin Piotr , Iota Valentin , Weinstein Bernie A. , Teisseyre Henryk , Suski Tadeusz , Hersee Steeve , Kisielowskil Christian , Weber Eicke R. , Yang Jinwei
Published: April 2011

We have studied the pressure dependence of photoluminescence for various InGaN quantum wells of different Indium compositions. In contrast to classical quantum well systems such as GaAs/AlGaAs, the pressure coefficients of the photoluminescence peak position of wells of similar parameters can vary greatly, depending on conditions of growth. Generally, the pressure coefficient of the emission peak is much lower than the one predicted for a GaN-InN system. We show that this behavior can be related in most cases to the influence of the thick GaN layer compressibility on the strain in the InGaN quantum wells. However, in some cases (Nichia devices), the pressure coefficient of the emission peak seems to be unrelated to the shift of the energy gap of the material, suggesting the involvement of strongly localized electronic states
A New Approach to Growth of Bulk Zno Crystals for Wide Bandgap Applications
Authors: Agarwal G. , Nause J. E. , Hill D. N.
Published: April 2011

A novel technique was used to melt zinc oxide powder. This techniques involves the pressurized RF induction heating of ZnO, contained in a water-cooled crucible. The ability to obtain a pool of molten ZnO enables the pulling of large diameter ZnO crystals using conventional melt growth processes. Centimeter-sized crystals were obtained in the preliminary experiments by cooling the ZnO melt. These crystals were analyzed for crystalline perfection and stoichiometry using x-ray diffiraction and photoluminescence. The semiconductor properties of these crystals were also measured. This technology can potentially provide large, low cost ZnO single crystal wafers for use in the fabrication of GaN blue diodes and blue lasers, high temperature / high power FETs, as well as homoepitaxy of ZnO wide band-gap devices. Single crystal zinc oxide also has potential application in the piezoelectric device market.
Optical Anisotropy Studies of Sapphire by Raman Scattering and Spectroscopic Transmission Ellipsometry
Authors: Yao H. , Yan C. H. , Denbaars S. P. , Zavada J. M.
Published: April 2011

Optical anisotropy of sapphire have been studied by both polarized Raman scattering and transmission variable angle spectroscopic ellipsometry (TVASE). The polarized Raman effect was measured on both c-plane (0001) and a-plane (2110) sapphire substrates. Two TO phonons (379 and 431 cm−l) and four LO phonons (418, 450, 577, and 750 cm−1) were observed when the optical axis  is perpendicular to the polarization of the incident laser beam (for both c-plane and a-plane). While only two TO phonons (379 and 431cm−1) and two LO phonons (418 and 645 cm−1) can be seen when the optical axis is parallel to the polarization for an a-plane sapphire. The optical axis of the a-plane sapphire can then be quickly determined by either maximizing or minimizing the 645 LO peak intensity with about ±10° error. TVASE measurements were carried out in the energy range of 0.75eV to 5.8eV at room temperature. Sizable off-diagonal Jones matrix elements Apst, and Aspt can be detected even with the optical axis 1° off the X-axis. This indicates that TVASE has a high sensitivity to optical anisotropy. By minimizing these off-diagonal elements and combining the Raman analysis, the optical axis orientation of an a-plane or m-plane (0110) sapphire can therefore be fully determined with an error of less than 1°.
Interaction of Nitrogen With 6H-SiC Surfaces
Authors: Elsbergen V. Van , Rohleder M. , Mönch W.
Published: April 2011

The interaction of nitrogen with 6H-SiC surfaces with different orientation and composition ranging from Si-rich to graphitized was investigated by use of X-ray and ultraviolet photoemission spectroscopy (XPS, UPS). The samples were cleaned and their surface composition was tuned by heating them in a Si flux at different temperatures or by annealing. Nitrogen exposures were performed using a RF plasma source operated at 13.56 MHz. Two different nitridation mechanisms can be distinguished by XPS. While anion exchange occurs at bulk-truncated SiC surfaces diffusion will control the nitrogen uptake of Si-rich samples. After nitridation, UPS spectra of bulk–truncated surfaces display characteristic valence-band structures of Si3N4. The thickness of the nitride layer amounts to approximately 9–12 Å. Thicker silicon nitride films on SiC are obtained by rising the sample temperature during nitrogen exposures or by deposition and subsequent nitridation of thin Si overlayers on SiC surfaces. The nitrogen uptake of graphitized samples is comparable to that of bulk-truncated surfaces. Our photoemission spectroscopy results prove that surface graphite is partly removed by N and the UPS spectra point to the formation of silicon nitride. In addition, C-N bonds exist but the exact bonding configuration cannot be resolved.
Ultra-High Implant Activation Efficiency In GaN Using Novel High Temperature RTP System
Authors: Cao X. A. , Abernathy C. R. , Singh R. K. , Pearton S. J. , Fu M. , Sarvepalli V. , Sekhar J. A. , Zolper J. C. , Rieger D. J. , Han J. , Drummond T. J. , Shul R. J. , Wilson R. G.
Published: April 2011

Si+ implant activation efficiencies above 90%, even at doses of 5×1015 cm−2, have been achieved in GaN by RTP at 1400–1500°C for 10 secs. The annealing system utilizes with MoSi2 heating elements capable of operation up to 1900 °C, producing high heating and cooling rates (up to 100 °C · s−1). Unencapsulated GaN show severe surface pitting at 1300 °C, and complete loss of the film by evaporation at 1400 °C. Dissociation of nitrogen from the surface is found to occur with an approximate activation energy of 3.8 eV for GaN (compared to 4.4 eV for AIN and 3.4 eV for InN). Encapsulation with either rf-magnetron reactively sputtered or MOMBE-grown AIN thin films provide protection against GaN surface degradation up to 1400 °C, where peak electron concentrations of ∼5×1020 cm-3 can be achieved in Si-implanted GaN. SIMS profiling showed little measurable redistribution of Si, suggesting Dsi ≤ 10-13 cm2 · s−1 at 1400 °C. The implant activation efficiency decreases at higher temperatures, which may result from SiGa to SiN site switching and resultant self-compensation.
High Voltage Silicon Carbide Devices
Authors: Baliga B. Jayant
Published: April 2011

Progress made in the development of high performance power rectifiers and switches from silicon carbide are reviewed with emphasis on approaching the 100-fold reduction in the specific on-resistance of the drift region when compared with silicon devices with the same breakdown voltage. The highlights are: (a) Recently completed measurements of impact ionization coefficients in SiC indicate an even higher Baliga's figure of merit than projected earlier. (b) The commonly reported negative temperature co-efficient for breakdown voltage in SiC devices has been shown to arise at defects, allaying concerns that this may be intrinsic to the material. (c) Based upon fundamental considerations, it has been found that Schottky rectifiers offer superior on-state voltage drop than P-i-N rectifiers for reverse blocking voltages below 3000 volts. (d) Nearly ideal breakdown voltage has been experimentally obtained for Schottky diodes using an argon implanted edge termination. (e) Planar ion-implanted junctions have been successfully fabricated using oxide as a mask with high breakdown voltage and low leakage currents by using a filed plate edge termination. (f) High inversion layer mobility has been experimentally demonstrated on both 6H and 4H-SiC by using a deposited oxide layer as gate dielectric. (g) A novel, high-voltage, normally-off, accumulation-channel, MOSFET has been proposed and demonstrated with 50x lower specific on-resistance than silicon devices in spite of using logic-level gate drive voltages. These results indicate that SiC based power devices could become commercially viable in the 21st century if cost barriers can be overcome.
A New Development Of Scanning Hydrogen Imaging System And Its Application
Authors: Ueda Kazuyuki , Ishikawa Ken'ichi , Yoshimura Masamichi
Published: April 2011

Scanning type electron-stimulated desorption (ESD) spectroscopy to detect hydrogen on solid surfaces has been described. To analyze a two-dimensional distribution of hydrogen on solid surface, a pencil-type fine-focused electron gun, of which spot size is less than 300 nm at 800 eV, has been developed using a thermal field emitter. The lateral resolution of analysis is achieved less than 1 μm.

Letters were drawn on a hydrogen-terminated Si(100) surface by irradiation of continuous electron beam to remove hydrogen from the surface, and by the following scanning ESD measurement, a clear letters were confirmed on this surface. Direct lithography by an electron beam on silicon surfaces has been realized.
Neutron scattering studies of the structures and Vibrational Dynamics of the HCP Rare-Earth Trihydrides
Authors: Udovic T. J. , Huang Q. , Rush J. J.
Published: April 2011

Both neutron-powder-diffraction and neutron-vibrational-spectroscopy studies have been undertaken to characterize the structures and vibrational dynamics of a variety of bulk hcp rareearth trihydrides RH3 (where R = Y, Th, Dy, Ho, Er, and Lu). The results are consistent with P3c1 as the prevalent structural symmetry for all trihydrides investigated except LuH3. Corresponding results for LuH3 are suggestive of an atypical arrangement of H atoms. Preliminary analyses of LuD3 diffraction patterns indicate that the main peaks can be satisfactorily modeled using P63/mmc symmetry with a reduced unit cell, although numerous minor diffraction features and a relatively unusual vibrational spectrum hint at either a more complex structure or an unknown secondary phase. The deviations from P3c1 symmetry are likely a consequence of the relatively smaller metal-hydrogen bond distances for LuH3.
The Influence of Nitrogen Implantation on the Hydrogen Distribution in Titanium Observed by Nra and Xps
Authors: Soltani-Farshi M. , Baumanna H. , Baretzky B. , Rück D. , Bethgea K.
Published: April 2011

Titanium has a strong chemical affinity and can absorb and store large amounts of hydrogen, which causes embrittlement of the material. Ion implantation is applied to improve wear behavior e.g. of titanium alloys, which are used for load bearing components of hip and knee joint prostheses. Nitrogen implantation influences the hydrogen content in the near surface region of a commercially available pure titanium. 150 keV 15N-ions were implanted at RT into titanium samples with a fluence of 6 × 1017 ions/cm2 and subsequently annealed at 500°C under high vacuum conditions. For comparison N was also implanted at a sample temperature of 500°C. Concentration depth profiles of implanted nitrogen and accumulated hydrogen were measured with Nuclear Reaction Analysis (NRA) and compared to nitrogen and titanium depth profiles obtained with X-ray Photoelectron Spectroscopy (XPS). The results indicate a relation between hydrogen concentration and the formation of Ti-N bonds.
Is an Arsenic-Antisite-Defect a Constituent of Hydrogen-Related:Metastable Defects (M3/M4) In GaAs?
Authors: Okumura T. , Shinagawa T.
Published: April 2011

The hydrogen-related metastable defects (M31M4) in n-GaAs, first found by Buchwald et al., were introduced only in the crystals containing the EL2 center. Off-center oxygen (=EL3), could not be responsible for their formation. A quantitative analysis with the samples exposed to atomic hydrogen showed that the M4 defect consisted of two different configurations. One of them did couple with M3, but is latent in the as-exposed state. It was formed after bias annealing at higher temperatures, such as 420 K. The other part of the M4 defect (M4•) existed at room temperature and after annealing at 513K, but disappeared and reappeared upon forward- and reverse-bias annealings, respectively.
Hydrogen Incorporation into CU-III-VI2 Chalcopyrite Semiconductors
Authors: Otte K. , Lippold G. , Grambole D. , Herrmann F. , Schlemm H. , Schindler A. , Bigl F.
Published: April 2011

We implanted at 300 eV into Cu-chalcopyrite semiconductors at temperatures between 50°C and 300°C. The surface chemistry is similar to the previously reported behavior of CuInS2 implanted with a H2+, H+ low energy ion beam [1] with respect to secondary phase etching. We also found an increase of radiative recombination (photoluminescence), which had been attributed to defect passivation and, hence, as an indicator of hydrogen incorporation [2]. Under the 300 eV implantation conditions, however, we observed neither a hydrogen concentration in a few hundred nm surface range exceeding the NRA detection limit of about 1×1019 cm-3 nor a pronounced stoichiometry variation in the ternary material, as proved by Raman measurements.

We conclude, therefore, that a 300 eV implantation introduces significantly less atomic hydrogen into the volume of the sample than previously reported for other beam compositions under similar temperature and current density conditions. This could be a result of the very low energy of less than 100 eV which can be expected for atomic H produced by dissociation of 300 eV at the surface, making the instant out-diffusion into the high vacuum of the implantation chamber a favored process.
Nmr Study in Sodium-Hydrogen-C60 Superconductor
Authors: Ogata H. , Miyajima S. , Imaeda K. , Inokuchi H.
Published: April 2011

23Na and 1H NMR studies have been carried out for a NaxHyC60 superconductor The peak position of the 23Na NMR spectrum exhibits discontinuous upfield shift of 30 ppm at about 250 K, indicates a first order phase transition From the line shape of the 23Na spectrum obtained at 7 K, the quadrupole coupling constant tensor is evaluated to be |e2Qq/h|=3.7 MHz with the asymmetry parameter η = 0.95. The 1H NMR spectrum suggests an anionic hydrogen state with weakly delocalized nature.
EPR Study of the Role of Hydrogen in the Defect Formation Upon Heat Treatment of Oxidized SiC
Authors: Macfarlane P. J. , Zvanut M. E.
Published: April 2011

For the past several years hydrogen incorporation in metal oxide semiconductor (MOS) devices has been of interest because studies have shown that vacuum annealing of oxidized Si substrates desorbs hydrogen, revealing interfacial defects. Today, in applications that require higher power and/or temperature, Si will likely be replaced with a wide-band-gap semiconductor. For MOS devices, SiC is a leading contender because it can be thermally oxidized to form a SiO2 insulating layer similar to Si. However, the SiC/SiO2 structure potentially contains hydrogen sensitive centers similar to those found in Si/SiO2 structures. Using electron paramagnetic resonance (EPR), we have observed a center 1.8 G wide peak-to-peak at g=2.0026. The center is generated in oxidized SiC that has received a 900° C dry, N2 or O2, post oxidation heat-treatment in which moisture is measured to be less than 1 ppm. Annealing at 900° C in standard Ar containing at least 50 ppm H2O decreases the center's concentration by two orders of magnitude. By comparing results from our study to studies of Si-H and C-H bonds in a-SiC:H [1] and SiC converted graphite [2], we suggest that this center is related to carbon dangling bonds created by the effusion of hydrogen during the dry heat-treatment. We will compare the activation energy for the hydrogen depassivation of our center with that found for other C-H and Si-H systems.
Effect of Substitutions at the Nickel Site on the Electronic Structure of LaNi5 and its Hydrides
Authors: Gupta M.
Published: April 2011

The effect of Ni substitution in LaNi5 by 3d and s-p elements on the electronic structure of the intermetallic and its hydrides has been investigated using the self consistent linear muffin tin orbital (LMTO) method in the atomic sphere approximation (ASA). The Fermi level, EF, of LaNi4M (M = Fe,Co,Mn) is found to lie in the narrow additional M 3d subband above the Ni d states, leading to an increase in the density of states (DOS) at EF. In contrast, the substitution of Ni by an s element of the 3d series, Cu, or by an s-p element: Al or Sn results in a progressive filling of the Ni-d bands and in a decrease of the DOS at EF. In all the substituted intermetallic compounds, we find that the lattice expansion accounts for less than 50% of the observed decreased stability, this shows the importance of the effect of chemical substitution. We also discuss the factors which affect the electronic structure and the stability of the hydrides and compare our results with available experimental data.
Properties of Mg2NiH4 at 450-570 K
Authors: Guthrie S. E. , Thomas G. J. , Noreus D. , Ronnebro E.
Published: April 2011

It has been established that Mg2NiH4 undergoes a phase change around 500°K in which the orientation of the NiH4 complex is quenched in a monoclinic distortion of the cubic high temperature phase. This results in the formation of domains in which the lattice distortion is accommodated by microtwinning. These effects can be absent when the hydride phase is formed below the transition temperature. Microscopic analysis verifies a similar basal cubic structure in the low temperature phase; however, the domains and microtwins are absent in this material and it can readily be destabilized by thermal stresses induced by the electron beam. It is of interest to measure and compare the effect of the lattice differences on the thermodynamic properties of the low temperature versus the high temperature hydride phases. We report the equilibrium PCT data and hydrogen desorption kinetics of the two hydrides in the temperature range of 450–570 K.
Comparison of the Electromigration Behavior of Al(MgCu) with Al(Cu) and Al(SiCu)
Authors: Li Hua , Witvrouw Ann , Jin Sing , Bender Hugo , Maex Karen , Froyen Ludo
Published: April 2011

Mg is one of the elements that are regarded as having a beneficial effect on the Al electromigration (EM) lifetime. In this paper, we compare the EM behavior of 0.4 μm wide passivated Al-1%Mg-0.5%Cu, Al-0.5%Cu and Al-l%Si-0.5%Cu lines. Plan-view transmission electron microscopy and focused ion beam imaging reveal that Al(MgCu) film undergoes bimodal grain growth. Auger electron spectroscopy and secondary ion mass spectrometry show a strong surface segregation and a severe bulk depletion of Mg. Additionally the line-width dependence of the rate of the resistivity decay during aging shows also a different behavior for Al(MgCu) compared to Al(Cu) and Al(SiCu). All these findings are consistent with the EM results that Al(MgCu), processed with our experimental conditions, has both the lowest median time to failure and deviation in time to failure. The results are discussed in the light of the effect of Mg addition on the microstructure and of the great surface activity of Mg.
Growth, Patterning and Microelectronic Applications of Epitaxial Cobaltdisilicide
Authors: Mantl S. , Kappius L. , Antons A. , Löken M. , Klinkhammer F. , Dolle M. , Zhao Q. T. , Mesters S. , Buchal C H. , Bay H. L. , Kabius B. , Trinkaus H. , Heinig K. H.
Published: April 2011

We report on the epitaxial growth of CoSi2 on silicon using ion beam synthesis and molecular beam allotaxy. The latter process uses molecular beam epitaxy to grow a silicide precipitate distribution embedded in single crystalline silicon and thermal annealing to form the epitaxial layer. Both, ion beam synthesis and molecular beam allotaxy, are capable to grow epitaxial buried and surface CoSi2 layers on Si(100) and Si(111) of high quality.