bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyroelectric Properties of the Plt(10) Thin Film on the P-Doped Poly Silicon
Authors: Kang Seong Jun , Yoon Yung Sup , Kim Dong Il
Published: April 2011

We have studied the pyroelectric properties of the PLT(10) thin film deposited on a p-doped poly-Si electrode by using the sol-gel method. Measurement of the dielectric constant as a function of temperature shows the typical characteristics of a ferroelectric. The dielectric constant reaches a maximum at 295°C, which can be thought of as the Curie temperature. The PLT(10) thin film on p-doped poly-Si fabricated in this research shows excellent pyroelectric properties. The pyroelectric coefficient and the fiqures of merit, Fv and FD at room temperature are measured as 5.76 × 10−8 C/cm2 °C, 1.17 × 10−10C-cm/J and 0.93 × 10−8C-cm/J, respectively.
Characterization of SrxBa1−xTiO3 Pulsed Laser Deposition Thin Films
Authors: Pérez W , Sen Sampriti , Cordero J. , Ching-Prado E. , Katiyar R.S. , Horwitz J.S. , Knauss L.A.
Published: April 2011

Thin films of SrTiO3 (STO) and SrxBa1−xTiO3 (SBT) with x = 0.35, 0.5, 0.9, and prepared by excimer laser deposition on LaAlO3 and MgO were studied. SEM analysis indicates that the surfaces of these films are smooth with isolated pores, except the SBT(x=0.5)/LaAlO3 sample, where a high concentration of large pores was found. X-ray diffraction (XRD) results show well oriented films. External FT-IR reflection studies reveals a band around 500 cm−x, which shows a significant frequency shift with increasing component concentration. Also, this IR-reflectivity band presents no changes between the SBT(x=0.9)/LaALO3 sample annealed at 750°C and the same film annealed at 850°C. On other hand, the STO/LaAlO3 and STO/MgO films show differences in frequency position of this reflectivity band. Raman spectra of the SBT sample with x ≥ 0.35 show broad bands associated with the BaTiO3 (BTO) material. However, all the phonons bands are broader than those in BTO, in particular the band around 309 cm−. Raman results suggest that the spectrum is a consequence of a breakdown in the translational symmetry due to defects. Raman scattering also indicates a similarity between SBT(x=0.9) at 750°C and that at 850°C. Micro-Raman and EDX analysis show that STO/MgO and SBT(x=0.35)/LaAlO3 films are close to the expected stoichiometry, while STO/LaAlO3 and SBT(x=0.9) films present deficiencies of titanium and oxygen.
Mechanical Properties of Metal-Intermetallic Microlaminate Composites
Authors: Heathcote J. , Odette G. R. , Lucas G. E. , Rowe R. G.
Published: April 2011

Tensile strengths, static and dynamic fracture toughness, and fatigue crack propagation were measured for different combinations of Nb metal-intermetallic microlaminate composites. Metal layer bridging produced toughening by factors of 2 to 5 under static conditions. Dynamic testing reduced the toughness significantly. Fatigue crack propagation rates were comparable to data for pure Nb. A key composite property, the stress -displacement function σ(u) of the constrained metal layers, was evaluated by several techniques and used in a bridging-crack stability analysis to predict tensile strengths in agreement with experimental values. The results provide guidelines for improving microlaminate performance.
The Fracture Behavior of SiCp/Aluminum Alloy Composites With And Without Large Al-Particles
Authors: Pandey A. B. , Majumdar B. S. , Miracle D. B.
Published: April 2011

JIc measurements were performed on a SiCp/Al-7093 MMC with controlled heat treatments, and the damage mechanisms were evaluated to understand the influence of microstructural parameters on the fracture toughness and crack resistance behavior. The deformed materials showed widely different damage and flow localization for different matrix microstructures. In an effort to improve fracture toughness, large Al particles were incorporated into the powder-metallurgy based MMC, and extruded to obtain pancake shaped Al phases. In the extruded condition, the effect of Al particles on the crack initiation toughness was negligible. However, significant improvement in the toughness was observed when the extruded material was further rolled. These issues are discussed in the context of observed deformation and damage mechanisms.
The Structural Investigation of Alumina and Aluminum Nitride Mixed Thin Films Prepared by D.C. Plasma Processes Under Different Conditions
Authors: Wang Paul W. , Sui Shixian
Published: April 2011

Composite films of aluminum nitride and alumina were fabricated on 6061 aluminum alloys in a d.c. plasma chamber. Samples were treated by three main processes. They were 1) Ar plasma etching, 2) NH3/Ar plasma with low pressure and low current density, and 3) NH3 plasma with high pressure and high current density. The oxygen-free Al surface was obtained after 10 min. 2.8 keV Ar+ sputtering in a UHV analysis chamber after the sample was treated by processes 1 and 2. Composite films of aluminum nitride and alumina were obtained on samples treated by processes 1, 2, and 3. The surface compositions and bonding environments of the composite films were characterized by AES and XPS. Composite films containing Al-N, Al-O and Al-Al bonds were formed but no nitrogen-oxygen bonds were observed. The thicknesses of the films were estimated by argon sputtering in the UHV chamber. The surface morphologies of samples after fabrication processes in d.c. plasma were investigated by SEM. A possible formation mechanism of the composite film in the ammonia plasma is proposed.
Nanoindentation Studies of Yield Point Phenomena on Gold Single Crystals
Authors: Corcoran S. G. , Colton R. J. , Lilleodden E. T. , Gerberich W. W.
Published: April 2011

Nanoindentation studies often show an instantaneous displacement-excursion in the loaddisplacement curve. This anomaly is generally associated with a surface contamination effect, dislocation emission, a phase transition, or an oxide break-through event. The determination of which effect is operative is often difficult when investigating oxide covered surfaces. We have performed a detailed nanoindentation study on clean, flame annealed single-crystal Au thus eliminating the effects of a surface oxide or contamination layer. Multiple displacement excursions were observed exhibiting a new phenomenon of “staircase” yielding. Owing to the fact that our radius of contact is more than an order of magnitude smaller than the average dislocation spacing expected for well annealed Au, the excursions are explained in terms of multiple dislocation nucleation events on parallel slip bands. Indentation data were taken on Au (111), (110), and (100) single crystal surfaces.
Mechanical Properties of Pure Carbon and Carbonnitrogen Coatings on Thin Film Head Sliders
Authors: Wang G. , Strojny A. , Sivertsen J. M. , Judy J. H. , Gerberich W. W.
Published: April 2011

The mechanical properties of pure carbon (C) and carbon-nitrogen (C:N) coatings on thin film head sliders were investigated by continuous drag testing (CDT) and nano-indentation. Comparisons were made in terms of wear protection, elastic modulus and hardness of these two types of carbon films. The C and C:N thin films with various thickness were deposited on thin film head sliders using a facing target sputtering (FTS) system. After 23,000 revolutions of CDT tests, all the testing head sliders which were uncoated and coated with 90 Å C or C:N exhibited some degree of wear damage as indicated in AFM micrographs where that of the uncoated head was the most severe and that of the C:N coated head was the least. Head sliders coated with 1000Å C and C:N were studied under the TriboscopeTM nano-indenter, where load-displacement curves at different maximum loads were recorded. Elastic modulus and hardness were determined from those curves. The results show that elastic modulus and hardness of C:N are greater than that of C. Therefore, one may conclude that both C and C:N behave like a protective coating for the head slider where C:N is better than C, which could be well related to the larger elastic modulus and hardness of C:N.
Film Thickness Effect on Tensile Properties and Microstructures of Submicron Aluminum Thin Films on Polyimide
Authors: Kang Y. S. , Ho P. S. , Knipe R. , Tregilgas J.
Published: April 2011

The mechanical behavior of the metal film on a polymer substrate becomes an important issue in microelectronics metallization. The metal/polymer structure is also useful to investigate the deformation behavior of very thin free-standing metal film since the flexible polymer serves as a deformable substrate. The tensile force-elongation curves have been measured using a microtensile tester for aluminum thin films, deposited on a PMDA-ODA polyimide film, in the thickness range from 60 rum to 480 nm. The stress-strain curves for aluminum films were constructed by subtracting these curves with polyimide curves measured separately. Tensile strength increases linearly with decreasing film thickness from 196 MPa to 408 MPa within the film thickness range studied. This is in good agreement with the published data for free-standing aluminum films in the same thickness range. The measured Young's modulus is lower than the bulk modulus and exhibits no systematic dependence on the film thickness. The microstructures of aluminum films have been examined using a transmission electron microscope (TEM). These films posses the (111)-textured columnar grain structures. Grain sizes exhibit log-normal distributions and the mean grain size increases monotonically with the film thickness. An attempt is made to evaluate the effect of film thickness and grain size on the strength of aluminum thin film and the result is discussed.
Measurements of Stress Evolution During Thin Film Deposition
Authors: Chason E. , Floro J. A.
Published: April 2011

We have developed a technique for measuring thin film stress during growth by monitoring the wafer curvature. By measuring the deflection of multiple parallel laser beams with a CCD detector, the sensitivity to vibration is reduced and a radius of curvature limit of 4 km has been obtained in situ. This technique also enables us to obtain a 2-dimensional profile of the surface curvature from the simultaneous reflection of a rectangular array of beams. Results from the growth of SiGe alloy films are presented to demonstrate the unique information that can be obtained during growth.
Dependence of Hardness and Stiffness on Density of Ta2O5 and TiO2 Layers
Authors: Baker S. P. , Ottermann C. R. , Laube M. , Rauch F. , Bange K.
Published: April 2011

Highly refractive amorphous TiO2 and Ta2O5 films with thicknesses between 270 and 514 nm were deposited on fused silica glass substrates by reactive evaporation and reactive ion plating. Density, hardness, and stiffness were investigated as a function of deposition process. The films were examined using Rutherford backscattering spectroscopy and were found to have densities between 72 and 100% of those of the corresponding bulk oxides. Nanoindentation studies indicated a strong correlation between density and both hardness and elastic stiffness of the oxide film materials. Hardness and modulus both varied by more than 40% over this density range.
Studies of Interface Demarcation and Structural Defects in Ga Doped Ge Single Crystals Using Synchrotron White Beam X-Ray Topography
Authors: Chung H. , Raghothamachar B. , Zhou W. , Dudley M. , Gillies D. C.
Published: April 2011

Synchrotron White Beam X-ray Topography (SWBXT) has been applied to the characterization of marked growth interfaces in Ga doped Ge single crystals. The techniques employed in interface demarcation include modifications of the cold zone temperature, mechanical pulsing and Peltier pulsing. As revealed by our observations, the visibility of growth interfaces is a sensitive function of diffraction conditions. A combination of the correct orientation of the active reciprocal lattice vector with respect to the interface plane and the necessary strain sensitivity controlled by the rocking curve width of the reflection are proved to be important for interface visibility. This can easily be achieved by using synchrotron radiation since the tunability of the synchrotron source provides great flexibility in the choice of proper diffraction conditions. Structural defects such as small-angle tilt boundaries and dislocation cell structures were also observed. The formation mechanism of these defects will be discussed. Direct evidence of dislocations present in the seed crystal propagating into the as-grown crystal through the melt-back interface during crystal growth was also obtained.
X-Ray Spectroscopic Study of the PdxC60Chemical Bonding
Authors: Okotrub A.V. , Fomin E.S. , Ivanova V.N. , Mazalov L.N.
Published: April 2011

The CKα -emission spectra of the PdxC60 compounds were obtained. To interpret the spectrum and study the Pd - C60 chemical bond structure, the SCF Xα-SW calculations of the clusters simulating the bonding between two fullerene molecules and a Pd bridge atom were carried out. On the base of the obtained data, a diagram of the electron interaction between the Pd atoms and fullerenes was constructed.
Magnetic Circular Dichroism And X-Ray Absorption Near Edge Structure Studies Of Magnetoresistive Oxides
Authors: Mini S. M. , Mitchell John , Hinks D. G. , Kimball C. W. , Montano P. A. , Lee P. , Rosenmann D. , Tkachuk A. V. , Udani A.
Published: April 2011

We report the results of temperature dependent, Mn K-edge X-ray Absorption measurements: Magnetic X-ray Circular Dichroism (MXCD) for local magnetic properties and X-ray Absorption Near Edge (XANES) for electronic and structural properties of Mn-based oxide magnetoresistive compounds La1−xSrxMnO3. This is the first report of an MXCD signal of the Mn K-edge in Mn oxide systems. By studying the integrated peak intensity of the first peak in the MXCD signal, it can be determined that the magnetic properties of the system are independent of temperature in the range 94 to 223K.
Effects of Addition of Heavy Rare-Earth Elements on the Structures and Resistivities of Al Thin Films for TFT - LCD Interconnects
Authors: Takayama Shinji , Tsutsui Naganori , Zhudan Zheng
Published: April 2011

The addition of Ho or Er to Al thin films markedly suppresses the grain growth at high temperature (350 °C – 450 °C). However, different from the effect of adding elements of Y, La, Pr, Nd, Sm, Gd, and Dy, thermal defects of hillocks or whiskers start to appear on the film surface after annealing at 300 °C ( though depending on the content of added elements). It has been revealed that small amounts of metallic compounds of Al3RE (RE = Ho and Er) have been segregated in a supersaturated solid solution of the Al phase after annealing at 300 °C, and that a large amount of added impurities still remained in the Al matrix. The resistivity of Al1−xREx alloy thin films (RE = Ho or Er, x = 2 – 7 atomic %) was 5 – 7 μΩcm after annealing at 450 °C.
A Molecular Dynamics Simulation on Thin Film Formation Process of Surfactant-Mediated Growth
Authors: Sasajima Y. , Iijima A. , Ozawa S. , Hiki Y.
Published: April 2011

The phenomenon of surfactant-mediated growth has been successfully simulated by means of a molecular dynamics method using two-dimensional model atoms interacting via a Lennard-Jones potential. Surfactant atoms were placed on a substrate, and then film atoms were deposited. Under adequate experimental conditions, the surfactant atoms could stay at the growing surface by exchanging their positions with the deposited atoms. Effects of various conditions on the morphology of the film surface were precisely investigated by the simulations.
Influence of Substrate Misorientation on Facet Formation in Selective Area Metalorganic Chemical Vapor Deposition
Authors: Shin Hyunchol , Kwon Young-Se
Published: April 2011

We have investigated the influence of substrate misorientation on facet formation in selective area metalorganic chemical vapor deposition (MOCVD) on GaAs (001) vicinal substrates. Macroscopic steps several hundred angstroms high were generated on the epitaxial layer over triangular voids where the voids were formed using the conditions of the reverse–mesa–shaped facets. AFM observations revealed that the macroscopic steps were formed by the combined effects of the growth rate enhancement and the development of the exact (001) crystallographic surface. Through removing the growth rate enhancement effect from the experiment results, it could be expected that the exact (001) surface developed only on the side for which the (001) surface was exposed because the surface energy of a low index plane was lower than that of a misoriented high index plane.
Microstructure of Compositionally Modulated InAlAs
Authors: Twesten R. D. , Millunchick J. Mirecki , Ahrenkielt S. P. , Zhangt Yong , Lee S. R. , Follstaedt D. M. , Mascarenhast A. , Jones E. D.
Published: April 2011

We have observed spontaneous, lateral composition modulation in tensile InAlAs alloy films grown as short-period superlattices on InP (001). We have analyzed these films using transmission electron microscopy, x-ray reciprocal space mapping, and polarized photoluminescence spectroscopy. We find the growth front is nonplanar, exhibiting ∼2nm deep cusps aligned with the In-rich regions of the compositionally modulated films. In addition to the measured 15nm wavelength modulation in the [110] direction, a modulation of 30nm wavelength is seen in the orthogonal [110] direction. The photoluminescence from the modulated layer is strongly polarized and red shifted by 0.22eV.
Thin Film Growth as a Result of Cluster-Surface Collisions: Computational Simulations
Authors: Qi L. , Sinnott S. B.
Published: April 2011

Molecular dynamics simulations have been performed to investigate the chemical and structural processes which occur when molecular clusters of acetylene impact a non-rigid, hydrogenterminated diamond (111) surface at incident hyperthermal kinetic energies. The atoms are characterized by a realistic many-body empirical potential for hydrocarbon systems. The goal is to study the initial stages of thin film growth following impact. Important processes observed during the simulations include polymerization of the cluster molecules, and adsorption (tethering) of some polymer chains to the surface in the initial stages of thin film growth. Further simulations will be necessary to fully determine the characteristics of the film.
STM and X-Ray Diffraction Temperature-Dependent Growth Study of SrRuO3 PLD Thin Films
Authors: Hawley M. E. , Jia Q. X. , Brown G. W.
Published: April 2011

SrRuO3 (SRO) has recently found a number of applications in different fields, e. g. as a buffer layer for the growth of high temperature superconductor (HTS) YBa2Cu3O7-x films and as a bottom electrode for ferroelectric or high dielectric constant thin film capacitors and nonvolatile data storage. The growth of high crystallinity SRO films with good structural and electrical properties is the prerequisite for each of these applications. In this paper we describe the affect of one growth parameter, temperature (T), on the crystalline quality, epitaxial substrate relationship and resulting electrical properties. SRO films were deposited on LaAlO3 single crystal substrates by pulsed laser deposition at substrate temperatures (Ts) ranging from room temperature (RT) up to 800° C with a nominal film thickness of 150 nm range. The resulting films were characterized by x-ray diffraction, 4-point transport, and STM.

The films' microstructures, as revealed by STM, evolved from polygranular at RT to a layered plate-like structure at higher deposition temperatures, Ts. Increasing Ts was marked first by increasing grain size, then a stronger orientational relationship between film and substrate, finally followed by the development of increased connectivity between grains to an extended island or condensed layered state. The transition from polygranular to layered structure occurred at Ts > 650° C. Increased conductivity paralleled the changes in microstructure. The surfaces of all of the films were relatively smooth; the oriented films are suitable for use as conductive templates in multilayer structures.
Laser Assisted Molecular Beam Deposition of Si, C and Sic Films
Authors: DeLeon R. L. , Sun L. , Rexer E. , Charlebois J. , Garvey J. F. , Forsythe E. W. , Tompa G. S.
Published: April 2011

Laser Assisted Molecular Beam Deposition (LAMBD) utilizes a train of gas pulses to precisely control the flux of species generated by laser ablation. We have used the LAMBD technique to ablate Si, C or SiC and grow films on a variety of substrates. These films were deposited as a function of a variety of source growth parameters. Source emission spectra of the Si ablation showed atomic Si and Si+; C ablation showed C atoms. Flux control was implemented by a variation of the laser pulse energy. Flux rates were determined by ablation target mass differences. The films have been analyzed by Raman scattering, SEM, EDX, FTIR, ESCA and surface profile measurements to determine the film structure and composition. These results demonstrate the potential of using LAMBD sources as a means of depositing a variety of high quality single and multiple component films.
Influence of Hcl and H2 on the Heteroepitaxial Growth of 3C-SiC Films on Si(100) Via Low-Temperature Chemical Vapor Deposition
Authors: Edgar J. H. , Gao Y.
Published: April 2011

The roles of HCl and H2 on the low temperature epitaxial growth of 3C-SiC on Si (100) in the SiH4-C2H-HCl-H2 system were examined. At a deposition temperature of 1000 °C with pure H2 as the carrier gas, the deposition rate decreased by approximately 70%, and the structure of the films changed from randomly oriented polycrystals, to textured polycrystals, to single crystals as the Cl/Si gas input ratio was increased from 0 to 40. Without any HCl present, the deposition rate did not change when the H2 carrier gas was replaced with up to 75% He. With a Cl/Si input ratio of 40, the growth rate decreased by approximately 70% as the He fraction was increased to 75%. Films deposited without HCl became more textured as H2 was replaced with He, and single crystal films were produce with a 75% He - 25% H2 mixture as the carrier gas. In contrast, with an input Cl/Si ratio of 40, all films were single crystal, but the rocking curve FWHM increased as H2 was replaced with He.
Nanostructure Study of Ti/TiN Multilayers: Effect of the Deposition Temperature
Authors: Labdi S. , Sant C. , Hennet L. , Houdy Ph.
Published: April 2011

In this paper, we report on the growth and the study of Ti/TiN nanometric multilayers. The preparation of these films has been carried out by high vacuum diode r.f. sputtering. Growth was in-situ monitored by kinetic ellipsometry. Deposition temperature was kept to room and low temperature (-120°C) respectively in order to modify the interface properties and consequently to understand the effect of the interfaces on the film's mechanical properties.

The thickness of each layer was varied from 1 nm to 10 nm and alternately repeated in order to obtain a total thickness of 200 nm. After deposition, films were characterized by means of X-ray diffraction and grazing X-ray reflectometry for structural determination. This study shows that the TiN-Ti boundary is composed of TiNx, with x going from the nominal nitrogen concentration of the TiN layer to 0. This can be due either to a surface reaction of the incident titanium during the Ti sequence with the nitrogen present at the film surface or to a reaction of nitrogen with the target surface during the TiN sequence.
Competitive Motions of Grain-Boundary and Free Surface in Selecting Thin Film Morphology
Authors: Sun B. , Suo Z. , Yang W.
Published: April 2011

During annealing of a polycrystalline thin film, grain-boundaries and film surfaces move. If the grain-boundaries move faster, the grains having the lowest free energy grow at the expense of others, resulting in a continuous film with large grains. If the film surfaces move faster, they groove along their junctions with the grain-boundaries, breaking the film to islands. This paper describes analytic solutions for steady surface motions, and discusses the morphology selection.
Experimental Variables Effecting Chain Growth in Conductive Adhesives
Authors: Hefner Rebecca E. , Palmer Mark A.
Published: April 2011

Chains of conductive particles within a polymer matrix can be used in place of solder joints in electronics manufacturing. Such materials can be made such that electrical conduction occurs in only one direction. Fabricating such an electrical contact requires that the conducting particles be aligned and touching, thus providing a continuous path. This can be done by applying an electric field to a mixture containing conducting particles in a polymer. Preliminary work will be presented assessing the effect of electric field strength (applied voltage), viscosity (temperature), frequency (DC and AC) on the kinetics of chain formation. A designed experiment showed only viscosity or temperature to be statistically significant. However, it is believed that voltage and frequency are factors which will effect the chain kinetics. Specifically it is proposed that there is an optimal combination of frequency and voltage for chain formation. Based on these results a more systematic study has been proposed.
Vibrational Analysis of a Stearic Acid Adlayer Adsorbed on a Silver Flake Substrate
Authors: Miragliotta Joseph , Benson Richard C. , Phillips Terry E.
Published: April 2011

A surface vibrational study of a stearic acid/silver (Ag) flake system is reported. The chemical nature of this interfacial system was examined with surface enhanced Raman scattering (SERS) as a function of sample temperature. The SERS spectrum from the room temperature flake exhibited vibrational peaks that were attributed to a carboxylate species bound to the Ag substrate through the oxygen atoms in the terminal end group. The surface species remained stable to temperatures up to 150 °C, above which a partial decomposition to an amorphous carbon layer was observed. In addition to the Raman studies, an IR‐visible sum‐frequency (SFG) measurement from a stearic acid/smooth Ag substrate proved a useful probe of the C‐H stretches in the terminal methyl group of the molecule. The SFG signal from the asymmetric C‐H stretch in the methyl group exhibited a temperature dependence that was similar to the SERS response from the surface carboxylate group, namely, a marked and irreversible decrease in signal levels for temperatures above 150 °C.
Mechanical Deformation Modeling of Diamond/Gaas Structures
Authors: Strifas Nickolaos , Christou Aris
Published: April 2011

In this study a finite strain elastic-plastic finite element analysis is performed on diamond/GaAs structures. A series of models based upon the principal of superposition are proposed to investigate the mechanical deformation and thermal stress behavior of the diamond/gas structure due to coefficients of thermal expansions (CTE) mismatches. The interfacial shear and peeling stresses in multilayered stacks subjected to uniform temperature variation are studied. Finite strain elastic – plastic analysis is performed on a crack which lies on the interface between the diamond and gas materials. The ductile fracture from the tip of the interface crack, the stress and strain fields and distribution of microvoid volume fraction are analyzed.
A Novel, Low-Cost C-C Composite Heat Sink Material
Authors: Kowbel W. , Chellappa V. , Withers J.C.
Published: April 2011

Rapid advances in high power electronics packaging require the development of new heat sink materials. Advanced composites designed to provide thermal expansion control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C) composits are under consideration for several military and space electronic applications including SEM-E electronic boxes. The high cost of C-C composits has greatly hindered their wide spread commercialization. A new manufacturing process has been developed to produce high thermal conductivity (over 400 W/mK) C-C composites at greatly reduced cost (less than $50/lb). This new material has potential applications as both a heat sink and a substrate. Dielectric coatings such as A1N and diamond were applied to this new type of heat sink material. Processing, as well as mechanical and thermal properties of this new class of heat sink material will be presented.
Characterization of Metal/A1xIn1-xN Interface Thermal Stability and Electrical Properties
Authors: Qiu Guohua , Chen Fen , Olowolafe J. O. , Swann C. P. , Unruh K. M. , Holmes D. S.
Published: April 2011

The interfaces between metals and semiconductors are very crucial to the performance and reliability of solid-state devices. At the moment information on the interfaces between metals and group III-nitride semiconductors are very rare. In this study, linear I-V characteristics of titanium and aluminum to A1xIn1-xN of three different composition (x=0.18, 0.50,0.85) were obtained exhibiting ohmic characteristics. Specific contact resistance of these metals to A1.18In.82N and Al.5In.5N was measured by transmission line measurement. Interdiffusion between the metals and the semiconductors, induced by annealing in N2 ambient, was determined using RBS and thermal stability was evaluated.
On the Epitaxy of Metal Films on GaN
Authors: Liu Q.Z. , Smith K.V. , Yu E.T. , Lau S.S. , Perkins N.R. , Kuech T.F.
Published: April 2011

A variety of metal films deposited at room temperature have been found to grow epitaxially under conventional vacuum conditions on GaN grown by metalorganic vapor phase epitaxy on sapphire substrates. The metal films have been characterized by X-ray diffraction using a thin-film Read camera and by MeV ion channeling measurements. Lattice mismatch between the epitaxial metals and the GaN basal planes ranges from ∼ 0.2% to ∼ 22%, and does not appear to be the determining factor in the epitaxy reported here. Surface structure of the epitaxial metal films has been studied by atomic force microscopy and found to differ considerably from that of nonepitaxial metal films grown on similar GaN substrates.
Influence of Surface Defects on the Characteristics of GaN Schottky Diodes
Authors: Duboz J-Y. , Binet F. , Laurent N. , Rosencher E. , Scholz F. , Harle V. , Briot O. , Gil B. , Aulombard R. L.
Published: April 2011

We have studied the fabrication of Pt/Au Schottky diodes on n-type GaN. We show that the electrical characteristics of the diodes are strongly dependent on the surface chemical treatment before the metal deposition. Lowest leakage currents were obtained by the use of a HC1 solution. We also show that annealing the diode at a moderate temperature (400°C) leads to reduced reverse currents. In order to explain these results, we measured the density of deep levels in the Schottky diode depletion region before and after the annealing process. We did not observe any significant difference in the bulk density of defects due to the anneal. We also studied the temperature dependence of the reverse currents and found a low activation energy. Our results are interpreted in terms of electrical defects at the metal-GaN surface.
MOCVD Growth of GaN Films on Lattice-Matched Oxide Substrates
Authors: Kryliouk O. M. , Dann T. W. , Anderson T. J. , Maruska H. P. , Zhu L. D. , Daly J. T. , Lin M. , Norris P. , Chai H. T. , Kisker D. W. , Li J. H. , Jones K. S.
Published: April 2011

The use of the nearly lattice-matched oxide substrates LiGaO2 and LiAlO2 has been explored for growth of GaN by MOCVD. As compared to the quality of films grown on sapphire, only growth on LiGaO2 yielded good quality films, and required use of nitrogen as the carrier gas. Furthermore, high structural quality films were grown on LiGaO2 at temperatures as low as 850°C. Dislocation densities estimated from cross-sectional TEM micrographs were found to be as low as 107 cm-2 . HRTEM studies revealed deformations at the surface of the LiGaO2 adjacent to deposited GaN films, indicating possible interracial reactions which may affect the film properties. The GaN film orientations corresponded directly to the substrate orientation, viz., ({0001}/{001} and {1102}/{101}).
Growth of GaN by Sublimation Technique and Homoepitaxial Growth by MOCVD
Authors: Sakai Shiro , Kurai Satoshi , Nishino Katsushi , Wada Koichi , Sato Hisao , Naoi Yoshiki
Published: April 2011

The growth of bulk GaN by sublimation method and a homoepitaxial growth by MOCVD are reported. A photo-pumped stimulated emission is obtained from a homoepitaxial layer. The source powder used as a source in the sublimation method is investigated in detail, and it is shown that the powder contains many kinds of compounds consisting mainly of gallium, nitrogen and hydrogen. Growth nucleation control is performed by partly covering an MOCVD-GaN or a scratched-sapphire (0001) by Si02. Hexagonal columns of the size of about 200 μm in diameter and about 200 μm in height are selectively and uniformly grown at the window sites. This technique enables the device processing of crystallites and also helps to increase crystal size by increasing growth time, since it prevents the nucleation of new crystallites which work as sink of the growing species.
Reactive MBE Growth of GaN and GaN:H on GaN/SiC Substrates
Authors: Johnson M. A. L. , Yu Zhonghai , Boney C. , Hughes W. C. , Cook J. W. , Schetzina J. F. , Zhao H. , Skromme B. J. , Edmond J. A.
Published: April 2011

Reactive N and H, created using rf plasma sources, were used to grow undoped GaN along with p-type GaN:Mg and p-type GaN:Mg:H thin films. By comparing the optical emission spectra from several rf sources with observed GaN grow rates, we deduce that nitrogen atoms and I stpositive series nitrogen molecules (3.95 eV binding energy) are the reactive species responsible for GaN film growth. A Mg ground state acceptor binding energy of about 224 meV was determined from low temperature photoluminescence (PL) experiments for both p-type GaN:Mg and p-type GaN:Mg:H films.
Metalorganic vapor phase epitaxial growth of GaInN/GaN hetero structures and quantum wells
Authors: Scholz F. , HÄrle V. , Steuber F. , Sohmer A. , Bolay H. , Syganow V. , DÖrnen A. , Im J.-S. , Hangleiter A. , Duboz J-Y. , Galtier P. , Rosencher E. , Ambacher O. , Brunner D. , Lakner H.
Published: April 2011

GaInN/GaN heterostructures and quantum wells have been grown by low pressure metalorganic vapor phase epitaxy on sapphire using an AIN nucleation layer. We found a significant In incorporation only for growth temperatures of 700°C, although still very high In/Ga ratios in the gas phase had to be adjusted. The In content could be increased by reducing the H2/N2 flow ratio in the main carrier gas. GaInN layers typically show two lines in low temperature photoluminescence which are identified as excitonic-like (high energy peak) and impurity-related-like (low energy) by time-resolved spectroscopy. Quantum wells with a thickness between 8 and 0.5 nm showed only one emission line. The peak of the thinnest wells shows excitonic-like behaviour, whereas we found a smooth transition to an impurity-related-like type with increasing thickness. By scanning transmission electron microscopy studies we found indications for composition fluctuations in these thicker quantum wells which may cause localization effects for the excitons and thus be responsible for the observed optical spectra.
Selected Energy Epitaxy of Gallium Nitride
Authors: Chilukuri R. K. , Zhang Suian , Chen E. , Davis R. F. , Lamb H. H.
Published: April 2011

A new apparatus for III-V nitride growth by selected energy epitaxy (SEE) is described. The multi-chamber system comprises a doubly differentially pumped molecular beam source, UHV-compatible growth chamber, x-ray photoelectron spectroscopy (XPS) chamber, UHV transfer line, and loadlock. The growth chamber is equipped for in situ quadrupole mass spectrometry and reflection high-energy electron diffraction (RHEED). Preliminary results of GaN SEE using hyperthermal beams of trimethylgallium (TMG) and ammonia (NH3) are presented.
Mechanisms of Strain Reduction in GaN and AlGaN/GaN Epitaxial Layers
Authors: GfrÖrer O. , Schlüsener T. , Härle V. , Scholz F. , Hangleiter A.
Published: April 2011

We have investigated Al0.12Ga0.88N layers with and without a 1 µm GaN buffer, grown on the c-face of α – Al2O3 substrate with an intermediate AlN nucleation layer grown by LP-MOVPE. We used spatially resolved cathodoluminescence spectroscopy at a temperature of 8K to investigate the strain and the homogeneity of composition that can be determined from the energy of the luminescence peak. The larger thermal expansion coefficient of the sapphire in comparison to the nitrides leads to a biaxial compressive strain of the upper GaN layer when cooling down from growth temperature. For AlGaN layers directly grown on the nucleation layer this cannot be confirmed. The layer stays relaxed and fluctuations in the aluminium composition of 0.4% can be observed. When growing an intermediate GaN buffer, the AlGaN layer gets tensilely strained. This strain is of elastic nature and microcracks can be observed preferentially at the edges due to the smaller lattice constant of AlGaN in comparison to GaN. Even detaching of the AlGaN layers grown on the buffer can be observed. In the regions without cracks the layers are quite homogeneous. A deformation potential of (19±4)eV was estimated for Al0.12Ga0.88N.
N-K-Edge EXAFS Study of Epitaxial GaN Films
Authors: Katsikini M. , Paloura E. C. , Fieber-Erdmann M. , Moustakas T. D. , Amano H. , Akasaki I.
Published: April 2011

X-ray absorption measurements at the N and O-K-edges are used to study the local microstructure in cubic and hexagonal GaN films grown by ECR-MBE and HVPE. A distortion in the local microstructure is identified in the 1st nearest neighbor (nn) shell, consisting of Ga atoms, in both the cubic and hexagonal samples. Two N-Ga distances are identified, R1 and R2, where R1 is the expected distance of 1.95Å while R2=R1+0.25Å. The same distortion is detected in the next nn shell containing Ga atoms, where the two distances are 3.7Å and 4.1Å. All the reported distance variations are larger than the error-bar. The nitrogen 2nd nn neighbor is found at the expected distance of 3.12Å while N deficiency is not detected. Finally, the O-Ga distance is found equal to 1.60Å and therefore it can be proposed that the oxygen atom occupies interstitial positions.
High Resolution X-ray Diffraction of GaN Grown on Sapphire Substrates
Authors: Saxler A. , Capano M. A. , Mitchel W. C. , Kung P. , Zhang X. , Walker D. , Razeghi M.
Published: April 2011

X-ray rocking curves are frequently used to assess the structural quality of GaN thin films. In order to understand the information given by the line shape, we need to know the primary mechanism by which the curves are broadened. The GaN films used in this study were grown by low pressure metalorganic chemical vapor deposition (MOCVD) on (00•1) sapphire substrates. GaN films with both broad and very narrow (open detector linewidth of 40 arcseconds for the (00•2) GaN reflection) rocking curves are examined in this work. Reciprocal space maps of both symmetric and asymmetric reciprocal lattice points are used to determine that the cause of the broadening of GaN rocking curves is a limited in-plane coherence length.
Intrinsic Mobility Limits of a Two-Dimensional Electron Gas in AlGaN/GaN Heterostructures
Authors: Walukiewicz W. , Hsu L. , Redwing J. M.
Published: April 2011

We present the results of a theoretical study of the 2D electron gas mobility at a AlxGa1−xN/GaN heterointerface. All standard mechanisms, including scattering by acoustic and optical phonons, and remote and background (residual) impurities have been included in our calculation of theoretical mobility limits in a AlxGa1−xN/GaN structure. Comparison of calculations with experimental mobilities obtained from high quality MOCVD grown Al0.15Ga0.85N/GaN heterostructures shows that the low temperature mobility in these samples is dominated by scattering from ionized impurities, with a smaller contribution from acoustic phonons.
Observation of a Two-Dimensional Electron Gas in the AlGaN/GaN on SiC Substrates
Authors: Chi G. C. , Lin C. F. , Cheng H. C. , Huang J. A. , Feng M. S. , Guo J. D.
Published: April 2011

GaN/Al0.08 Ga0.92 N heterostructure has been grown on(0001) 6H-SiC substrates using low pressure metalorganic chemical vapor deposition(LP-MOCVD). Triethylgallium (TEGa), trimethylaluminum(TMA) and ammonia(NH3) were used as the Ga, Al and N sources, respectively. The carrier gas is hydrogen(H2)and the growth pressure is kept at 76 torr. Five pairs of GaN/Al0.08 Ga0.92N(100Å/100Å)were used as buffer layer, then follow by an 1.3 μ m GaN film. The 500Å AlGaN bulk structure was grown on the GaN and Finally an 100Å GaN cap layer to prevent the oxidation of AlGaN layer. The full width half maxima(FWHM) of x-ray peak is 115 arc second for the thick layer of GaN (1.3 μ m), this value is smaller than we reported for the GaN on sapphire substrate (It was about 300 arc second). The Hall mobility and sheet carrier concentration are 887 cm2/Vs, 1.0 × 1016cm-2 at 300K and 4661 cm2/Vs, 7.2 × 1012cm-2 at 77K. This high electron mobility is an indication of a two-dimensional electron gas(2DEG) formed at the GaN/AlGaN interface.
Coexistence of Shallow and Localized Donor Centers in Bulk GaN Crystals Studied by High-Pressure Raman Spectroscopy
Authors: Perlin P. , Suski T. , Polian A. , Chervin J. C. , Knap W. , Camassel J. , Grzegory I. , Porowski S. , Erickson J. W.
Published: April 2011

Character of the metal-insulator transition which occurs at about 23 GPa in bulk GaN crystals has been studied by means of high pressure Raman spectroscopy. The related freeze-out of electrons is caused by the localized donor state formed by most likely oxygen and emerging at high pressures to the band gap of GaN. As a result, the electron concentration drops from its initial value of 5.1019 cm-3 to about 3. 1018 cm-3. These remaining electrons originate likely from another donor center with effective mass character, probably carbon. The obtained results raise a question whether the nitrogen vacancy is abundant enough to be observed in bulk GaN crystals.
Magnetic Resonance Studies of GaN-Based Single- Quantum Well LEDs
Authors: Carlos W. E. , Glaser E. R. , Kennedy T. A. , Nakamura Shuji
Published: April 2011

We report electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AJGaN single-quantum-well light emitting diodes. The dominant feature detected by either technique is a broad resonance (ΔB ≈ 13 mT) at g ≈ 2.01 which is enhanced by high current stressing. Our ELDMR measurements show that, depending on bias, this defect is predominately associated with either an increase or a decrease in electroluminescence at resonance while our EDMR measurements show that this resonance is associated with an increase in current at resonance before stressing and a decrease after stressing. We suggest that this is associated with a nonradiative recombination path, in parallel with the radiative recombination path and with recombination in the depletion region of a contact. A second resonance, more prominent before stressing, with g ≈ 1.99 and ΔB ∽ 7 mT is very similar to the deep donor trap, previously observed in double heterostructure diodes and is associated with a decrease in both the current and electroluminescence at resonance.
Structural and Optical Properties of AlGaN/GaN Quantum-Well Structures Grown by MOCVD on Sapphire
Authors: Niebuhr R. , Bachem K. H. , Behr D. , Hoffmann C. , Kaufmann U. , Lu Y. , Santic B. , Wagner J. , Arlery M. , Rouviere J. L. , Jürgensen H.
Published: April 2011

AlGaN/GaN single quantum wells (QW) have been grown on 2” sapphire substrates (c-plane) by metal-organic chemical vapor deposition (MOCVD). The well width was varied between 20 and 40 Å for barriers containing 4 % and 16 % of aluminium. Cathodoluminescence (CL) and Photoluminescence (PL) spectra of the samples show, as expected, a shift of the quantum well emission to higher energies with decreasing well width, whereas the barrier luminescence stays at constant energy. Examination of the QWs by resonant Raman spectroscopy tuned to the gap of the well, clearly shows the GaN A1(LO) phonon besides the AlGaN A1(LO) phonon from the barrier. For a well width of 20 Å we observe a shift of the A1(LO) GaN phonon indicating a certain degree of intermixing at the GaN/AlGaN interface. Atomic Force Microscopy (AFM) reveals that the layers are growing in a 2-dimensional step flow growth mode with step heights of 3 and 6 Å corresponding to mono- and biatomic steps. High Resolution Transmission Electron Microscopy (HRTEM) micrographs of the 40 Å well show a very low interface roughness of 1–2 atomic layers.
Bulk and Surface Electronic Structure of GaN Measured Using Angle-Resolved Photoemission, Soft X-ray Emission and Soft X-ray Absorption
Authors: Smith Kevin E. , Dhesi Sarnjeet S , Duda Laurent-C. , Stagarescu Cristian B , Guo J. H. , Nordgren Joseph , Singh Raj , Moustakas Theodore D
Published: April 2011

The electronic structure of thin film wurtzite GaN has been studied using a combination of angle resolved photoemission, soft x-ray absorption and soft x-ray emission spectroscopies. We have measured the bulk valence and conduction band partial density of states by recording Ga L- and N K- x-ray emission and absorption spectra. We compare the x-ray spectra to a recent ab initio calculation and find good overall agreement. The x-ray emission spectra reveal that the top of the valence band is dominated by N 2p states, while the x-ray absorption spectra show the bottom of the conduction band as a mixture of Ga 4s and N 2p states, again in good agreement with theory. However, due to strong dipole selection rules we can also identify weak hybridization between Ga 4s- and N 2p-states in the valence band. Furthermore, a component to the N K-emission appears at approximately 19.5 eV below the valence band maximum and can be identified as due to hybridization between N 2p and Ga 3d states. We report preliminary results of a study of the full dispersion of the bulk valence band states along high symmetry directions of the bulk Brillouin zone as measured using angle resolved photoemission. Finally, we tentatively identify a non-dispersive state at the top of the valence band in parts of the Brillouin zone as a surface state.
Polycrystalline Silicon Grown on Porous Silicon-on-Insulator Substrates
Authors: Hsu Klaus Y.J. , Lee C. H. , Yeh C. C.
Published: April 2011

Inexpensive full-wafer SOI substrates are appealing for various applications such as ULSI. As an attempt to achieve this goal, low-temperature deposition of silicon on novel porous Si-on-insulator (PSOI) substrates was performed in this work. The bottom insulator was obtained by anodically oxidizing a pre-formed porous silicon film in HCl solution. The thickness, uniformity and quality of the resulted bottom oxide layer as well as the residual porous silicon layer above were well-controlled. Low-temperature PECVD growth of silicon on the PSOI wafer was conducted by using the residual porous silicon as the seed. Cross-sectional TEM pictures and electron diffraction patterns showed that poly-Si films were formed on PSOI substrates under the conditions of 98% hydrogen dilution ratio, 20 Watts RF power, and 300°C substrate temperature. Further thermal annealing at 1050°C for 30 minutes significantly enhanced the crystallinity of the deposited films. Combined with the excellent insulation ability of the bottom oxide, the technique is suitable for future inexpensive full-wafer SOI fabrication.
Phosphorus Doping of Boron Carbon Alloys
Authors: Hwang Seong-Don , Dowben P. A. , Cheeseman A. , Spencer J. T. , Mcilroy D. N.
Published: April 2011

Phosphorus doped boron carbon alloy films were made by chemical vapor deposition from a single source compound, dimeric chloro-phospha(III) carburane ((C2B10H10)2(PCl)2). Phosphorus doped B5C materials exhibit increases in the band gap from 0.9 eV to 2.6 eV.