bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ohmic contacts to Si-implanted and un-implanted n-type GaN
Authors: Brown J. , Ramer J , ZHeng K. , Lester L.F. , Hersee S.D. , Zolper J 
Published: April 2011

ABSTRACTWe report on ohmic contacts to Si-implanted and un-implanted n-type GaN on sapphire. A ring shaped contact design avoids the need to isolate the contact structures by additional implantation or etching. Metal layers of Al and Ti/Al were investigated. On un-implanted GaN, post metalization annealing was performed in an RTA for 30 seconds in N2 at temperatures of 700, 800, and 900°C, A minimum specific contact resistance (rc) of 1.4×10−5 Ω-cm2 was measured for Ti/Al at an annealing temperature of 800°C. Although these values are reasonably low, variations of 95% in specific contact resistance were measured within a 500 µm distance on the wafer. These results are most likely caused by the presence of compensating hydrogen. Specific contact resistance variation was reduced from 95% to 10% by annealing at 900°C prior to metalization. On Si-implanted GaN, un-annealed ohmic contacts were formed with Ti/Al metalization. The implant activation anneal of 1120°C generates nitrogen vacancies that leave the surface heavily n-type, which makes un-annealed ohmic contacts with low contact resistivity possible.
Ohmic Contact Formation to Doped GaN
Authors: Smith L. L. , Bremser M. D. , Carlson E. P. , Weeks T. W. , Huang Y. , Kim M. J. , Carpenter R.W. , Davis R. F. 
Published: April 2011

ABSTRACTOhmic contact strategies for n- and p-type GaN have been investigated electrically, chemically, and microstructurally using transmission line measurements, high-resolution EELS and cross-sectional TEM, respectively. The contributions to contact performance from work function differences, carrier concentrations, annealing treatments, and interface metallurgy have been examined. The contact materials of Ti, TiN, Au, and Au/Mg were deposited via electron beam evaporation; Al was deposited via thermal evaporation. As-deposited Al and TiN contacts to highly doped n-GaN were ohmic, with room-temperature specific contact resistivities of 8.6×10−5 Ω cm2 and 2.5×10−5 Ωcm2 respectively. The Ti contacts developed low-resistivity ohmic behavior as a result of annealing; TiN contacts also improved with further heat treatment. For p-GaN, Au became ohmic with annealing, while Au/Mg contacts were ohmic in the as-deposited condition. The performance, structure, and composition of different contact schemes varied widely from system to system. An integrated analysis of the results of this study is presented below and coupled with a discussion of the most appropriate contact systems for both n- and p-type GaN.
Fabrication and Properties of AlGaN/GaInN Double Heterostructure Grown on 6H-SiC(0001)Si
Authors: Amano Hiroshi , Sota Shigetoshi , Nishikawa Masaki , Yoshida Masato , Kawaguchi Makoto , Ohta Masahiro , Sakai Hiromitsu , Akasaki Isamu 
Published: April 2011

ABSTRACTAlGaN/GalnN double heterostructures (DH) were fabricated by metalorganic vapor phase epitaxy on the (0001)Si 6H-SiC substrate. A cleaved edge shows a very flat surface with roughness on the order of one monolayer. Stimulated emission and laser action from the UV to blue region was observed by optical pumping at room temperature (RT). The threshold power density was 27KW/cm2 which is smaller than that of the same structure grown on a sapphire (0001) substrate by a factor of four. A AlGaN/GalnN DH UV light emitting diode, using undoped GalnN is fabricated. The power efficiency and spectra width of this LED is comparable or superior to that of an LED having the same structure but grown on sapphire.
Analysis of Wurtzite GaN/AlGaN Quantum Well Lasers from First-Principles Calculations
Authors: Uenoyama T. , Suzuki M. 
Published: April 2011

ABSTRACTOptical gain of wurtzite GaN/AlGaN quantum wells has been studied from a first-principles calculation using the k • p method. Most of the parameters in the k • p method were determined by fitting the band structures by the first-principles calculation. Owing to the small spin-orbit splitting energies of the wurtzite GaN and AIN, the optical gain has been calculated using the 6×6 Hamiltonian for the valence band. It is found that the large hole effective masses and the small spin-orbit splitting cause the higher threshold current density of wurtzite GaN/AlGaN quantum well lasers.
Non-Stoichiometric Transfer of Complex Oxides by Pulsed Laser Deposition at Low Fluences
Authors: Dam B. , Rector J.H. , Johansson J. , DE Groot DG. , Griessen R. 
Published: April 2011

ABSTRACTWe provide evidence that non-stoichiometric ablation of YBa2Cu3O7δ at low fluences is due to a phase separation of the target surface. On the other hand, in SrTiO3 we find at low fluences evidence for preferential ablation which is assisted by volume-diffusion. As a result, the Sr/Ti ratio of the ablated films can be tuned by choosing the appropriate fluence.
KrF Laser-Induced Nanometer Si Crystallites Formation and Tem Observation
Authors: Huang Xinfan , Li Zhifeng , Wu Wei , Chen Xiaoyuan , Li Wei , Hong Ling , Li Qi , Chen Kunji 
Published: April 2011

ABSTRACTWe report the preparation of the nanometer Si crystallites constrained between a-SiNx:H barrier layers by means of KrF excimer laser induced crystallization. X-ray diffraction (XRD) and Raman scattering spectra demonstrate that ultra thin a-Si:H well layers have been crystallized. The average grain size of Si crystallites is on the order of magnitude of a nanometer. Small-angle XRD spectrum indicates multilayer structures have not undergone laser damage. The results of TEM are presented to show smooth and abrupt interfaces of layered structures and nanometer Si crystallites arrayed one-by-one in the Si layer. The thermodynamics of KrF laser-induced crystallization of ultra-thin Si layer has been discussed.
Single shot excimer laser annealing of amorphous silicon: effect of hydrogen on the properties of the poly silicon
Authors: Boher P. , Stehle M. , Godard B. , Stehle J.L. 
Published: April 2011

ABSTRACTPECVD amorphous silicon films deposited at different temperatures on low cost glass substrates have been treated by a Single Shot Excimer Laser Annealing (SSELA) at various energy densities. The influence of a thermal treatment at medium temperature (400°C) prior to the SSELA treatment was also investigated. Spectroscopie ellipsometry and Raman characterizations show that hydrogen contamination produces an important roughness increase with very little polycrystalline grains (650nm) after laser treatment. The thermal treatment prior laser annealing improves drastically the structural quality of the films. Structural results are correlated with the electrical performances of the TFT produced on these films.
Surface modifications of fullerite induced by pulsed laser irradiation
Authors: Milani P. , Manfredini M. 
Published: April 2011

ABSTRACTThe formation of periodic patterns on fullerite thin film surfaces is observed after irradiation with a pulsed Nd:Yag laser (1064 nm). C60 disruption and subsequent coalescence of the fragments take place, resulting in the formation of carbon nanotubes and polyhedral hollow graphitic particles. The effects of irradiation have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman scattering.
Nitriding of Zirconia by Irradiation with NdrYAG Laser Beam
Authors: Fujitsu S. , Sawai M. , Kawamura K. , Hosono H. 
Published: April 2011

ABSTRACTThe surface of partially stabilized zirconia ceramics was irradiated by a Nd:YAG laser in various atmospheres. Zirconia strongly absorbed YAG's laser beam and changed its chemistry and microstructure. The change of color of zirconia into gold was due to the formation of zirconium nitride (ZrN) observed on the irradiated surface in air, nitrogen or ammonia, which was confirmed by X-ray diffraction and secondary ion mass spectroscopy. The observed ZrN phase was 10-20 um in thickness at the irradiated area by the direct beam. The adhesion between formed ZrN and YSZ substrate was very weak.
Instabilities and Structure Formation in Laser Processing
Authors: Bàuerle D. , Arenholz E. , Arnold N. , Heitz J. , Kargl P.B. 
Published: April 2011

ABSTRACTThis paper gives an overview on different types of instabilities and structure formation in various fields of laser processing. Among the examples discussed in detail are non-coherent structures observed in laser-induced chemical vapor deposition (LCVD), in laser-induced surface modifications, and in laser ablation of polymers.
Area Selective Laser Chemical Vapor Deposition of Diamond
Authors: Lindstam M. , Boman M. , Larsson K. , Stenberg G. , Carlsson J.-O. 
Published: April 2011

ABSTRACTHigh quality diamond spots were deposited on silicon substrates by a hot filament process combined with laser heating. A mixture of CH4(1.8 vol%) and H2was passed over a tantalum filament having a temperature of about 2200 °C. The substrate temperature was varied by small adjustments of the filament power. A focused laser beam was used to locally raise the temperature on the substrate surface. By a proper choice of filament temperature, background substrate temperature and laser induced temperature, isolated islands of polycrystalline diamond could be deposited on the silicon substrate. The deposited diamond spots were characterized by micro-Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and scanning force microscopy.
Dendrite Tip-Shape Characteristics
Authors: LaCombe J.C. , Koss M.B. , Bushnell L.T. , de Jager K.D. , Glicksman M.E. 
Published: April 2011

ABSTRACTThe assumption that dendrite tips are parabolic bodies of revolution pervades many of the theories and experiments addressing dendritic growth. This assumption, while reasonable, is known to become less valid as regions of interest further from the tip of the dendrite are considered. Experimental measurements were made on pure succinonitrile dendrites at several super coolings. The equation that describes the dendrite tip profile is extended from a second order polynomial (paraboloidal) form to one that includes higher-order terms. The deviation of a dendrite tip from a parabolic body of revolution can be characterized by a parameter obtained from the coefficient of the fourth-order term describing the profile. This dimensionless parameter, Q, is found to be a function of the profile orientation only, independent of supercooling.
Nucleation and Dendritic Growth in Undercooled Melts
Authors: Herlach Dieter M. 
Published: April 2011

ABSTRACTTechniques of containerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of both the undercooling and the crystal growth velocity. Experimental results are presented for studies of nucleation of metastable crystalline phases and quasicrystals. Measurements of the dendrite growth velocity as a function of undercooling are exemplified for dilute Ni-based alloys and intermetallics. The results are analysed within current theories of rapid crystal growth. Their consequences on the formation of grain refined microstructures are highlighted. In addition, recent experiments on the undercooling of magnetic alloys are discussed revealing the existence of long-range magnetic ordering in an undercooled melt.
The Early Stages of Solid-State Reactions in Ti/Al Multilayer Films
Authors: Michaelsen C. , WÖHlert S. , Bormann R. , Barmak K. 
Published: April 2011

ABSTRACTWe have investigated the solid-state reaction of Ti/Al multilayer films by x-ray diffraction (XRD) and differential scanning calorimetry (DSC), with focus on the early stages of the reaction provided by samples with pair thicknesses in the range 5 - 40 nm. This reaction, which results in formation of TiAl3 with metastable Ll2 structure, can be modeled by a nucleation and growth process on the basis of the Johnson-Mehl-Avrami theory, with a reaction-order parameter n ≈1. These observations indicate the significance of nucleation barriers even at early stages of solid-state reactions, and suggests that the phenomena of phase selection and formation of metastable phases can result from the presence of nucleation barriers.
Nucleation and Growth of the First Phase in Sputter-Deposited Nb/Al Multilayer Thin Films
Authors: Barmak K. , Vivekanand S. , Ma F. , Michaelsen C. 
Published: April 2011

ABSTRACTThe formation of the first phase in the reaction of sputter-deposited Nb/Al multilayer thin films has been studied by power-compensated and heat-flux differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The modulation periods of the films are in the range of 10-500 nm. Both types of calorimetrie measurements, performed at a constant heating rate, show the presence of two peaks (A and B) for the formation of the single product phase, NbAl3. Isothermal calorimetrie scans show that peak A is associated with a nucleation and growth type transformation. The formation of NbAl3 is thus interpreted as a two-stage process of nucleation and lateral growth to coalescence (peak A) followed by normal growth until the consumption of one or both reactants (peak B). Transmission electron microscopy investigations of samples annealed into the first stage of NbAl3 formation show the presence of this phase at the Nb/Al interface and its preferential growth along the grain boundaries of the Al layer. The latter highlights the role of reactant phase grain structure in product phase formation.
Interaction of Silicate Liquid with Sapphire Surfaces
Authors: Ramamurthy Sundar , Hebert Brian C. , Carter C. Barry , Schmalzried Hermann 
Published: April 2011

ABSTRACTThe wetting behavior of a calcium aluminosilicate liquid in contact with sapphire of four crystallographically different orientations has been investigated using scanning electron microscopy and atomic force microscopy. Continuous layers of glass films heat-treated at 1600°C and 1700°C result in dewet pockets of glass on the surface. The heat treatment also causes the alumina surfaces to facet which presents interesting shapes to the glass pockets. The morphology of the pockets with respect to the orientation of the facets is useful in understanding qualitatively the liquid-solid interfacial energies relative to the orientation of the facets. This approach enables a sequential study of the interaction between the facets and the silicate liquid. Based on temperature, the equilibrium composition of the silicate changes by solution-precipitation and evaporation processes which affects the facet and step morphology. This experiment directly emphasizes the relevance of anisotropy in the α-Al2O3 crystal structure which may ultimately control some of the key issues of materials’ processing.
Kinetic Competition During Duplex Partitionless Solidification in Ni-V Alloys
Authors: Allen D.R. , Perepezko J.H. 
Published: April 2011

ABSTRACTA structure composed of both partitionless face-centered cubic (α-fcc) and body-centered cubic (β-bcc) phases has been observed following high undercooling solidification of nickel-vanadium (Ni-V) alloys in the composition range 47-51.7 at.% V. Containerless processing and rapid solidification suppresses the formation of the equilibrium σ phase and results in the simultaneous formation of partitionless fcc and bec phases. Transmission electron microscopy analysis has identified regions in which 0.1-1 μηι a and β grains co-exist in a duplex structure. A nucleation and growth kinetics analysis has been developed to describe the conditions under which this structure may form. Thermodynamic and kinetic arguments have been used to provide bounds on various kinetic parameters. These bounds indicate that the nucleation rates for a and β must be larger than about 1027 m−3 s−3 to account for the number of grains observed in the time available for nucleation, and the growth rates are constrained to be larger than about 1 m/s to account for complete solute trapping.
Model Evaluations of Phase Diagrams of the Systems SrO - (Mn, Fe, Co, Ni)O
Authors: Revzin B. , Pelleg J. 
Published: April 2011

ABSTRACTA model of substitutional ionic solid solution is applied for prediction of excess energy and the construction of binary phase diagrams of the systems SrO-MnO, SrO-FeO, SrO-CoO and SrO-NiO.
A Mechanism for Supercooling in Organic Liquids
Authors: Thoma Paul E. 
Published: April 2011

ABSTRACTIn this investigation, a mechanism for supercooling in organic liquids is formulated. By comparing the melting temperature and spontaneous freezing temperature of the chemicals evaluated with their molecular characteristics, the factors promoting supercooling are developed. The results obtained indicate that the following molecular characteristics promote supercooling in organic liquids:sharing of electrons between the atoms of a molecule;A three-dimensional chemical structure;A permanent, three-dimensional, and partially charged pocket within the chemical structure;A partially charged projection having a charge opposite that of the pocket and located on the side of the molecule opposite that of the pocket.
A New Experimental Method for Investigating the Nucleation Kinetics of Solids in Supercooled Liquid Si
Authors: Jin Song H. , Im James S. 
Published: April 2011

ABSTRACTIn this paper, we first describe and then demonstrate the soundness of a new experimental method that is designed to deliver a wide range of accurately measured nucleation rates of solids in supercooled liquid Si. The method utilizes thin-film processes, as well as laser-quenching and detection techniques, in order to first induce isothermal transformation and then extract the corresponding solid nucleation rates over a frequency range potentially greater than ten orders of magnitude. The technological and scientific gains that can result from acquiring such information are discussed.
Morphology of Ag Islands Grown on GaAs (110) at Low Coverage: Monte Carlo Simulations
Authors: Challa A. , Drucker J. , Cale T.S. 
Published: April 2011

ABSTRACTThe growth morphology of Ag on GaAs (110) surfaces, at low coverages, is investigated with Monte Carlo simulations using a solid-on-solid model. Experimentally Ag deposited at room temperature forms 3D isotropic islands and forms needle-like islands elongated along the <110> direction when deposited at 250°C. Preliminary simulation results using 2D island growth model indicated that the elongation of islands at 250°C deposition is due to anisotropic surface diffusion and nearest-neighbor interactions along the <100> and <110> directions. The island morphologies obtained using a 3D island growth model are in good agreement with experimentally observed morphologies.
Structural Decomposition at Sn/GaAs(001) Interface
Authors: Nasr S. A. , Zinke-Allmang M. 
Published: April 2011

ABSTRACTMorphological studies of the system Sn/GaAs(001) are required to interpret electronic anomalies of devices which include doped III-V MBE grown thin films. Previous studies focused on the dynamics of Sn on As terminated surfaces. The current study complements those studies on a Ga terminated surface, i.e., conditions which may occur locally for short periods during MBE growth.Sn is deposited on in-situ cleaned Ga rich GaAs(001) surfaces and the evolution of morphological structures is presented as a function of annealing temperature and Sn supersaturation. Three distinct regimes were observed, (i) a low temperature range (T ≤ 500°C) where Sn shows a propensity toward three-dimensional clustering, (ii) an intermediate temperature range (500°C ≤ T ≤ 625°C) where a transition in the morphology occurs due to strong interactions with the substrate resulting in the formation of characteristic etch-patterns and (iii) a high temperature regime (T ≥ 650°C) where the thermal decomposition of GaAs dominates while the deposited Sn desorbs fast.
Step-Edge Barriers on GaAs(001)
Authors: Šmilauer P. , Vvedensky D.D. 
Published: April 2011

ABSTRACTWe investigate growth of GaAs(001) using kinetic Monte Carlo simulations of a very simple atomistic solid-on-solid model. The key features of this model are a short-range incorporation process of freshly deposited atoms and additional activation barriers to interlayer transport. Both are required to obtain close agreement between measured electron-diffraction intensities and simulated surface step densities during growth and post-growth equilibration on vicinal surfaces. This model is used to study long-time evolution of the surface morphology. Large pyramid-like features develop during growth on a singular surface which coarsen in time while maintaining an approximately constant slope. Growth on a vicinal surface is also found to be unstable. Simulated surface morphologies are compared with recent work using atomic-force microscopy. Finally, we show how a suitably modified version of this model helps to explain the recently observed phenomenon of re-entrant layer-by-layer chemical-beam etching of a singular GaAs(001) surface. The central features responsible for this behavior are the site selectivity of the etching process combined with step-edge barriers to interlayer adatom migration.
Heteroepitaxial Layer Morphology and Misfit Defect Formation
Authors: Cullis A.G. 
Published: April 2011

ABSTRACTThe manner in which misfit strain can influence the morphology of heteroepitaxial layers is reviewed. Following a brief consideration of theoretical modelling, examples of experimental observations for two important materials systems, SiGe/Si and InGaAs/GaAs, are given. It is demonstrated that the formation of undulations of specific types is driven by partial elastic stress-relief and a lowering of the system free energy. Under these conditions, islands of deposit can be formed during initial growth and ripples can be produced upon continuous layers. Furthermore, the presence of surface morphological distortions and the accompanying strain fluctuations also can have a significant impact upon misfit dislocation introduction. Relationships between these fluctuations and dislocation source behaviour are described.
Si1-xGex Critical Thickness for Surface Wave Generation During UHV-CVD Growth at 525°C
Authors: Lafontaine H. , Houghton D.C. , Bahierathan B. , Perovic D.D. , Baribeau J.-M. 
Published: April 2011

ABSTRACTSeveral Si1-xGex/Si heterostructures were grown at 525°C using a commercially available UHV-CVD reactor. Layers with a germanium fraction ranging from 0.15 to 0.5 were examined by means of cross-sectional transmission electron microscopy and atomic force microscopy. Surface waves were found in layers with a thickness above a critical value which decreases rapidly as the Ge fraction is increased. Both experimental and modeling results show that surface waves are generated before misfit dislocations for Ge fractions above 0.3.
Control of Defect Structures in CuGaSe2 Epitaxial Films
Authors: Chen Wei , Gu Gin-Lern , Tseng Bae-Heng 
Published: April 2011

ABSTRACTAn in-situ annealing process, which is conducted in the growth chamber by exposing the film to a Se beam immediately after film deposition, is developed to control defect structures in CuGaSe2 epitaxial films. TEM observations showed that the films annealed at a temperature above 450°C could completely remove anti-phase domain boundaries and effectively annihilate threading dislocations. The annealing process also changes the distributions of intrinsic point defects in the film. Photoluminescence (PL) may reflect the microstructure improvement in the films. A suppress of the donor-to-acceptor transitions caused by antisite defects and an enhancement in the PL intensity were found in a annealed film.