bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Speed Ge Photodetectors on Si Platform for GHz Optical Communications in C+L Bands
Authors: Liu Jifeng , Michel Jurgen , Cannon Douglas D. , Giziewicz Wojciech , Pan D. , Danielson David T. , Jongthammanurak Samerkhae , Yasaitis John , Wada Kazumi , Fonstad Clifton G. , Kimerling Lionel C. 
Published: April 2011

ABSTRACTWe present a high speed, high responsivity, tensile strained Ge p-i-n photodetector selectively grown on Si platform that covers the whole C band and a large part of the L band for high capacity optical communications. The device shows a 3dB bandwidth of 2.5GHz and its responsivities at 1310nm and 1550nm are comparable to commercial InGaAs photodetectors currently used in telecommunications. The device has promising applications in Si microphotonics such as the fiber-to-the-home technology.
Towards p-type doping of ZnO by ion implantation
Authors: Coleman V. A. , Tan H. H. , Jagadish C. , Kucheyev S. O. , Phillips M. R. , Zou J. 
Published: April 2011

ABSTRACTZinc oxide is a very attractive material for a range of optoelectronic devices including blue light-emitting diodes and laser diodes. Though n-type doping has been successfully achieved, p-type doing of ZnO is still a challenge that must be overcome before p-n junction devices can be realized. Ion implantation is widely used in the microelectronics industry for selective area doping and device isolation. Understanding damage accumulation and recrystallization processes is important for achieving selective area doping. In this study, As (potential p-type dopant) ion implantation and annealing studies were carried out. ZnO samples were implanted with high dose (1.4 × 1017 ions/cm2) 300 keV As ions at room temperature. Furnace annealing of samples in the range of 900°C to 1200°C was employed to achieve recrystallization of amorphous layers and electrical activation of the dopant. Rutherford backscattering/channeling spectrometry, transmission electron microscopy and cathodolumiescence spectroscopy were used to monitor damage accumulation and annihilation behavior in ZnO. Results of this study have significant implications for p-type doing of ZnO by ion implantation.
Latest developments in Blue-Violet Laser Diodes grown by Molecular Beam Epitaxy
Authors: Bousquet V. , Kauer M. , Johnson K. , Zellweger C. , Hooper S.E. , Heffernan J. 
Published: April 2011

ABSTRACTWe report on recent results obtained for InGaN multiple quantum well laser diodes grown by ammonia based Molecular Beam Epitaxy. The laser diodes were grown on freestanding GaN substrates and operated at room temperature under pulsed current injection conditions. For devices with improved p-type doping a threshold current density of 6.7kA.cm−2 was measured for a current pulse duration of 200ns and an operating temperature of 3.9°C. A duty cycle up to 50% with a pulsed injection current duration of 500μs was also achieved at 3.9°C.
Advances in AlGaN-based Deep UV LEDs
Authors: Crawford M. H. , Allerman A. A. , Fischer A. J. , Bogart K. H. A. , Lee S. R. , Chow W. W. , Wieczorek S. , Kaplar R. J. , Kurtz S. R. 
Published: April 2011

ABSTRACTMaterials studies of high Al-content (> 30%) AlGaN epilayers and the performance of AlGaN-based LEDs with emission wavelengths shorter than 300 nm are reported. N-type AlGaN films with Al compositions greater than 30% reveal a reduction in conductivity with increasing Al composition. The reduction of threading dislocation density from the 1–5 × 1010 cm-2 range to the 6–9 × 109cm-2 range results in an improvement of electrical conductivity and Al0.90Ga0.10N films with n= 1.6e17 cm-3 and μ=20 cm2/Vs have been achieved. The design, fabrication and packaging of flip-chip bonded deep UV LEDs is described. Large area (1 mm × 1 mm) LED structures with interdigitated contacts demonstrate output powers of 2.25 mW at 297 nm and 1.3 mW at 276 nm when operated under DC current. 300 μm × 300 μm LEDs emitting at 295 nm and operated at 20 mA DC have demonstrated less than 50% drop in output power after more than 2400 hours of operation. Optimization of the electron block layer in 274 nm LED structures has enabled a significant reduction in deep level emission bands, and a peak quantum well to deep level ratio of 700:1 has been achieved for 300 μm × 300 μm LEDs operated at 100 mA DC. Shorter wavelength LED designs are described, and LEDs emitting at 260 nm, 254nm and 237 nm are reported.
Efficient and Reliable Homoepitaxially-Grown InGaN-Based Light-Emitting Diodes
Authors: Cao X. A. , Teetsov J. M. , LeBoeuf S. F. , Arthur S. D. , Kretchmer J. 
Published: April 2011

ABSTRACTInGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission at ∼405 nm were grown on bulk GaN and sapphire substrates using MOCVD. Tunneling current was found to be dominant in the LED on sapphire over a wide range of applied bias, but was substantially suppressed in the homoepitaxial LED. Nanoscale electrical characterization using conductive atomic force microscopy (C-AFM) revealed highly localized leakage current at V-defects in the LED structure on sapphire, indicating that the associated threading dislocations were electrically active and behaved as leakage current pathways connected across the p-n junction. Compared to the lateral LED on sapphire, the vertically-structured LED on GaN had a reduced series resistance of 7 Ω and greatly improved power conversion efficiencies. The homoepitaxial LED was subjected to stress test at 400 mA for 24 h and showed minimal optical degradation, whereas the same stress resulted in the destruction of the LED on sapphire due to increased current crowding and self-heating.
A Model for the Critical Height for Dislocation Annihilation and Recombination in GaN Columns Deposited by Patterned Growth
Authors: Twigg M. E. , Bassim N. D. , Eddy C. R. , Henry R. L. , Holm R. T. , Mastro M. A. 
Published: April 2011

ABSTRACTIn order to reduce vertical leakage in III-nitride detectors, we have grown a patterned array of hexagonal GaN columns on masked heteroepitaxial GaN template layers using a-plane sapphire substrates. In addition to eliminating cracking, we have found that for GaN columns tens of microns in diameter and several microns high, the dislocation density is also significantly reduced. We have developed a simple closed-form analytical model for predicting the critical column height for the onset of the reduction in the dislocation density. Among the predictions of this model is that the critical column height for the onset of dislocation density reduction is proportional to the product of column width and the grain size of the GaN film.
Growth of GaN from elemental Gallium and Ammonia via Modified Sandwich Growth Technique
Authors: Berkman E. , Collazo R. , Schlesser R. , Sitar Z. 
Published: April 2011

ABSTRACTGallium nitride (GaN) films were grown on (0001) sapphire substrates at 1050°C by controlled evaporation of gallium (Ga) metal and reaction with ammonia (NH3) at a total reactor pressure of 800 Torr. Pure nitrogen (N2) was flowed directly above the molten Ga source to prevented direct reaction between the molten Ga and ammonia, which causes Ga spattering and GaN crust formation. At the same time, this substantially enhanced the Ga transport to the substrate. A simple mass-transport model based on total reactor pressure, gas flow rates and source temperature was developed and verified. The theoretical calculations and growth rate measurements at different ammonia flow rates and reactor pressures showed that the maximum growth rate was controlled by transport of both Ga species and reactive ammonia to the substrate surface.
Growth of Uncracked Al0.80Ga0.20N/GaN DBR on Si(111)
Authors: Charles M. B. , Kappers M. J. , Humphreys C. J. 
Published: April 2011

ABSTRACTThe strain in Al0.80Ga0.20N/GaN distributed Bragg reflectors (DBRs) grown by metalorganic vapour phase epitaxy (MOVPE) on Si(111) was studied using high resolution X-ray diffraction (XRD). Previous studies have shown that a 50nm Al0.80Ga0.20N layer induced a compressive strain in Al0.12Ga0.88N capping layers and prevented crack formation. A seven period Al0.80Ga0.20N/GaN DBR was grown, but this was found to be cracked at room temperature, despite compression in the GaN layers. This problem was solved by growing an identical structure with the addition of a 650nm GaN cap, and due to the compression in this layer, the structure was crack-free.
Polarity Control of GaN Films Grown by Metal Organic Chemical Vapor Deposition on (0001) Sapphire Substrates
Authors: Mita Seiji , Collazo Ramon , Schlesser Raoul , Sitar Zlatko 
Published: April 2011

ABSTRACTThe polarity control of GaN films grown on c-plane sapphire substrates by low pressure metal organic chemical vapor deposition (MOCVD) was achieved by using N2 as a diluent and transport gas. The type of polarity was governed by the substrate treatment prior to the GaN growth. N-face (-c) GaN films were only obtained by pre-nitridation of the sapphire substrate after a H2 anneal, while Ga-face (+c) GaN films were grown directly on the substrates or on properly annealed AlN buffer layers. In addition, GaN films on improperly annealed AlN buffer layers, that is, under- or over-annealed buffer layers, yielded films with mixed polarity. Smooth N-face GaN films with 2.5 nm RMS roughness, as determined by atomic force microscopy (AFM), were obtained with shorter nitridation times (less than 2 min). Wet chemical etching in an aqueous solution of potassium hydroxide (KOH) was used to determine the polarity type.
Near Field Optical Spectroscopy of GaN/AlN Quantum Dots
Authors: Neogi A. , Gorman B. P. , Morkoç H. , Kawazoe T. , Ohtsu M. , Kuball M. 
Published: April 2011

ABSTRACTWe investigate the spatial distribution and emission properties of self-assembled GaN/AlN quantum dots. High-resolution transmission electron microscopy reveals near vertical correlation among the GaN dots due to a sufficiently thin AlN spacer layer thickness, which allows strain induced stacking. Scanning electron and atomic force microscopy show lateral coupling due to a surface roughness of ∼ 50–60 nm. Near-field photoluminescence in the illumination mode (both spatially and spectrally resolved) at 10 K revealed emission from individual dots, which exhibits size distribution of GaN dots from localized sites in the stacked nanostructure. Strong spatial localization of the excitons is observed in GaN quantum dots formed at the tip of self-assembled hexagonal pyramid shapes with six [101 1] facets.
Resonantly enhanced second harmonic generation in a one-dimensional GaN-based photonic crystal slab
Authors: Torres Jérémi , d'Yerville Marine Le Vassor , Cassagne David , Legros René , Lascaray Jean-Paul , Centeno Emmanuel , Albert Jean-Paul , Coquillat Dominique 
Published: April 2011

ABSTRACTWe have performed investigations of resonance effects inside a gallium nitride one-dimensional photonic crystal slab in order to enhance the second-harmonic generated from an beam incident on the surface of the slab. Convenient conditions on the incident beam propagation direction and polarization are first identified by experimental or theoretical linear optical studies. Giant enhancements in the second-harmonic conversion have been obtained by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed by rotating the polarization of the fundamental beam.
Microstructure of highly p-type doped GaN sub-contact layers for low-resistivity contacts
Authors: Kröger R. , Dennemarck J. , Böttcher T. , Figge S. , Hommel D. 
Published: April 2011

ABSTRACTThe effect of a highly Mg doped subcontact layer on top of GaN grown by metal organic vapor phase epitaxy and its interface to a Pd/Au contact layer was investigated by means of transmission electron microscopy and electrical characterization techniques. Use was made of prior investigations of the Mg doping characteristics, which showed the existence of a segregation related defect free layer even for doping levels as high as 5×10−19cm−3, which thickness depends on the Mg to Ga molar precursor flow ratio. For a given subcontact layer thickness of 15 nm a critical precursor molar flow ratio of 0.035 resulted in a smooth surface showing an interfacial layer indicating a Pd/Ga alloying. This layer resulted in a contact resistivity as low as 2×10−5 Ωcm2. For a flow ratio of 0.070 the surface was found to be rough due to defect formation resulting in a contact resistivity as high as 10−3 Ωcm2 similar to the value obtained without subcontact layer. Moreover, the metallization layer showed in all cases a texture of the {111} lattice planes with respect to the {0002} planes of the GaN.
Impact of H2-preannealing of the Sapphire Substrate on the Crystallization of Low-Temperature-Deposited AlN Buffer Layer
Authors: Tsuda Michinobu , Balakrishnan Krishnan , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

ABSTRACTThe effect of H2-preannealing of sapphire substrate on low-temperature (LT- ) AlN buffer layer deposited by metalorganic vapor phase epitaxy is investigated. Crystallinity of LT-AlN drastically changes with preannealing temperature variation. It is found that H2-preannealing of sapphire substrate is a requisite to get a better quality LT-AlN and as a consequence it leads to growth of better quality GaN epi-layer on it.
Evidence of Carrier Mediated Ferromagnetism in GaN:Mn/GaN:Mg Heterostructures
Authors: Erdem Arkun F. , Reed Mason J. , Berkman Erkan Acar , El-Masry Nadia A. , Zavada John M. , Oliver Luen M. , Reed Meredith L. , Bedair Salah M. 
Published: April 2011

ABSTRACTDilute Magnetic Semiconductors (DMS's) posses a strong potential to make use of the spin of carriers in spintronic devices. Experimental results and theoretical calculations predict that GaN:Mn is a potential semiconductor material for spintronic device applications. The dependence of the room temperature ferromagnetic properties of GaN:Mn/GaN:Mg double heterostructures (DHS) on the Fermi level position in the crystal is demonstrated. Several GaN:Mn/GaN:Mg DHS are grown by metal organic chemical vapor deposition on sapphire. It is shown that initially paramagnetic films can be rendered ferromagnetic by facilitating carrier transfer through the GaN:Mn/GaN:Mg interface. Additionally, it is demonstrated that ferromagnetism depends on the thickness of the GaN:Mn and GaN:Mg layers. The carrier transfer process essentially changes the Fermi level position in the crystal. By choosing the right thicknesses for GaN:Mn and GaN:Mg an optimum DHS that exhibits room temperature ferromagnetism is grown. An identical structure, with the exception of insertion of an AlGaN barrier in order to obstruct the carrier transfer at the interface, results in paramagnetic films for AlGaN barriers thicker than 25nm. These results are explained based on the change in the occupancy of the 3d-Mn impurity band, and indicate that carrier mediation is the possible mechanism for the ferromagnetism observed in the MOCVD grown GaN:Mn material system. This is the first evidence that this material system responds to electronic perturbations, hence ferromagnetism observed is not due to secondary phases or spin glass behavior.
Raman Gain in Silicon Using Highly Confined Waveguide Structure
Authors: Xu Qianfan , Almeida Vilson R. , Lipson Michal 
Published: April 2011

ABSTRACTWe show ultra-fast Raman gain dynamics in submicron-size silicon-on-insulator strip waveguide. Using high confinement structures and pico-second pump pulses, we show 6-dB net nonlinear gain with 20.7-W peak pump power in a 7-mm long waveguide.
Classical versus ab initio structural relaxation: electronic excitations and optical properties of Ge nanocrystals embedded in a SiC matrix
Authors: Cappellini Giancarlo , Weissker H.-Ch. , De Salvator D. , Furthmüller J. , Bechstedt F. , Satta G. , Casula F. , Colombo L. 
Published: April 2011

ABSTRACTWe discuss and test a combined method to efficiently perform ground- and excited-state calculations for relaxed structures using both a quantum first-principles approach and a classical molecular-dynamics scheme. We apply this method to calculate the ground state, the optical properties, and the electronic excitations of Ge nanoparticles embedded in a cubic SiC matrix. Classical molecular dynamics is used to relax the large-supercell system. First-principles quantum techniques are then used to calculate the electronic structure and, in turn, the electronic excitation and optical properties. The proposed procedure is tested with data resulting from a full first-principles scheme. The agreement is quantitatively discussed between the results after the two computational paths with respect to the structure, the optical properties, and the electronic excitations. The combined method is shown to be applicable to embedded nanocrystals in large simulation cells for which the first-principle treatment of the ionic relaxation is presently out of reach, whereas the electronic, optical and excitation properties can already be obtained ab initio. The errors incurred from the relaxed structure are found to be non-negligible but controllable.
Theory of large-scale electronic structure calculation and nanostructures formed in silicon cleavage simulation: surface reconstruction, step and bending
Authors: Hoshi Takeo , Iguchi Yusuke , Fujiwara Takeo 
Published: April 2011

ABSTRACTSeveral methodologies are developed for large-scale atomistic simulations with fully quantum mechanical description of electron systems. The important methodological concepts are (i) generalized Wannier state and (ii) Krylov subspace. Test calculations are done with upto 106 atoms using a standard workstation. As a practical nanoscale calculation, the 10 nm scale structure in cleavage process of silicon is investigated. Discussions are focused mainly on the stable (experimentally observed) (111)-(2 × 1) cleavage process. Surface reconstruction and step formation are observed and compared with experiments. These processes are analyzed by the quantum mechanical freedoms of electron system, such as the local density of states (LDOS). We also observed the bending of cleavage plane into the (111) plane from other planes, which is a direct evidence of the stability of the (111) cleavage mode. Finally, several common aspects between cleavage and other phenomena are discussed from a general viewpoint of 10 nm scale structure.
Diamondlike Carbon-Metal Nanocomposite Films for Medical Applications
Authors: Narayan R. J. , Abernathy H. , Riester L. , Berry C. J. , Brigmon R. 
Published: April 2011

ABSTRACTSilver and platinum were incorporated within diamondlike carbon (DLC) thin films using a multicomponent target pulsed laser deposition process. Transmission electron microscopy of the DLC-silver and DLC-platinum composite films reveals that these films self-assemble into particulate nanocomposite structures that possess a high fraction of sp3-hybridized carbon atoms. DLC-silver-platinum films demonstrated exceptional antimicrobial properties againstStaphylococcusandPseudomonas aeruginosabacteria.
Comparison of -OH and -NH2 Functional Group Substitution on PTFE Surface with V-UV Photon Irradiation for Protein Adsorption
Authors: Sato Yuji , Kobayashi Naoki , Murahara Masataka 
Published: April 2011

ABSTRACTPoly-tetrafluoroethylene [PTFE] presents few rejections in a living body but has low tissue affinity. Then, the soft tissue implant material that has not only high biocompatibility but also superb bondability has been developed by photo-chemically substituting the hydrophilic of –OH or –NH2 groups on the PTFE surface with V-UV photon irradiation. The protein adsorption of the sample before and after treatment was also evaluated by scanning electron microscope [SEM] and attenuated total reflection Fourier-transform infrared [ATR FT-IR], using bovine serum albumin [ALB] and fibrin [FIB] solution as a protein index in biocompatibility test. From the results, it has been confirmed that the protein adsorption increased with the increase in the hydrophilic group's substitution density. The -OH incorporated sample adsorbed the ALB and FIB more than the -NH2 incorporated sample; the amount of the ALB and FIB sticking became 2.3 times larger than that of the non-treatment sample.
High-speed Processing with Reactive Cluster Ion Beams
Authors: Seki Toshio , Matsuo Jiro 
Published: April 2011

ABSTRACTCluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Especially, it is expected that extreme high rate sputtering can be obtained using reactive cluster ion beams. Reactive cluster ion beams, such as SF6, CF4, CHF3, and CH2F2, were generated and their cluster size distributions were measured using Time-of-Flight (TOF) method. Si substrates were irradiated with the reactive cluster ions at the acceleration energy of 5–65 keV. Each sputtering yield was increased with acceleration energy and was about 1000 times higher than that of Ar monomer ions. The sputtering yield of SF6 cluster ions was about 4600 atoms/ion at 65 keV. With this beam, 12 inches wafers can be etched 0.5 μm per minute at 1 mA of beam current. The TOF measurement showed that the size of SF6 cluster was about 550 molecules and the number of fluorine atoms in a SF6 cluster was about 3300. If the sputtered product was SiF, the yield has to be less than 3300 atoms/ion. These results indicate that the reactive cluster ions etch targets not only chemically, but also physically. This high-speed processing with reactive cluster ion beam can be applied to fabricate nano-devices.
Characterization of nanocrystalline surface layer induced by shot peening and effect on their fatigue strength.
Authors: Mano Hideo , Satoru Kondo , Matsumuro Akihito , Imura Toru 
Published: April 2011

ABSTRACTThe shot peening process is known to produce a hard layer, known as the white layer” on the surface of coil springs. However, little is known about the fatigue properties of this white-layer.In this study, coil springs with a white-layer were manufactured. The surface of these springs was then examined using micro Vickers hardness, FE-SEM etc. to test fatigue strength of the springs.From the results obtained, a microstructure of the white-layer with grain size of 50–100 nm was observed, with a Vickers hardness rating of 8–10 GPa.Tow category springs were manufactured utilizing a double-peening process. These springs had the same residual stress destruction and surface roughness. Only one difference was observed: one spring had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test realized an increase in the fatigue life of the nanocrystalline surface layer by 9%.
MOLECULAR DYNAMICS STUDY OF SUFACE STRUCTURE AND SPUTTERING PROCESS BY SEQUENCIAL FLUORINE CLUSTER IMPACTS
Authors: Aoki Takaaki , Matsuo Jiro 
Published: April 2011

ABSTRACTIn order to study the surface reaction process under cluster ion impact, molecular dynamics simulations of sequential cluster impacts of fluorine and neon clusters were performed. (F2)300 and Ne600 clusters were accelerated with totally 6keV and irradiated on bare Si(100) target. By iterating impact simulation sequentially, change of surface morphology and composition of desorbed materials were studied. In the case of fluorine cluster impact, the rough surface structure was made compared with neon cluster impact because fluorine atoms adsorb on the target, which work to keep pillar structure on the surface, whereas Ne atoms evaporate immediately leaving spherical mound structure on the surface. From the study of desorption process, it was observed that large number of Si atoms are desorbed in the form of silicon fluorides. The major sputtered material was SiF2, but various types of silicon-fluorides, including the molecules consists of several tens to hundreds silicon and fluorine atoms, were observed. The distribution of clusters in desorbed materials obeyed the classical model of cluster emission from quasi-liquid phase excited with ion bombardment. From these results, the irradiation effects of reactive cluster ions were discussed.