bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Status of and Challenges in CdTe Thin-Film Solar-Cell Technology
Authors: Compaan Alvin D. 
Published: April 2011

ABSTRACTPolycrystalline CdTe thin-film solar cells have shown high potential for low cost, large-area module fabrication. But successful large-scale commercial production has been elusive. Fabrication of the basic n-CdS/p-CdTe heterojunction is possible by a wide variety of methods, including close-spaced sublimation, vapor-transport deposition, electrodeposition, chemical bath deposition, and magnetron sputtering. An overview of these methods is presented as well as the role of the postdeposition “activation” treatment using CdCl2and issues related to the difficulty of obtaining low resistance back contacts to CdTe. We present some of our recent fabrication results using rf magnetron sputtering and discuss some of the advantages that appear possible from the use of sputtering methods in this class of materials. Some of these advantages are particularly relevant as the polycrystalline thin-film PV community addresses the challenges of fabricating tandem cells with efficiencies over 25%.
High-Rate Plasma Process for Microcrystalline Silicon: Over 9% Efficiency Single Junction Solar Cells
Authors: Matsui Takuya , Matsuda Akihisa , Kondo Michio 
Published: April 2011

ABSTRACTThis paper presents microcrystalline silicon (μ c-Si:H) p-i-n (superstrate-type) solar cells fabricated by 100 MHz plasma-enhanced chemical vapor deposition (PECVD) at i-layer deposition rates of >2 nm/s. Under high-rate conditions, in particular, the deposition pressure is found to play a dominant role in determining short circuit current (Jsc) of solar cell. With anincrease in deposition pressure from 3 to 7-9 Torr, Jsc increases by more than 50% due to a significant improvement in the long wavelength (>600 nm) responses, which essentially leads to high efficiency (∼8%) solar cells in the 2-3 nm/s deposition rate range. Further progress in solar cell efficiency has been made by the improvement of TCO/p and p/i interfaces. As a result, efficiency reaches 9.13% (Jsc=23.7 mA/cm2,Voc=0.528 V,FF=0.73) with a 2.3μm-thick i-layer grown at 2.3 nm/s. Transmission electron microscopy and secondary-ion mass spectroscopy studies reveal that samples prepared at lower pressure (∼4 Torr) comprise many grain boundaries due to disordered grain growth, which induces an anomalous incorporation of atmospheric impurities (predominantly oxygen) after exposing sample to air. In contrast, the high-pressure process (<7 Torr) provides denser grain columns coalesced with [110]-oriented crystallites, which in turn inhibits impurities from penetrating deeper in the film. Based on above results, we propose that the less post-oxidation behavior associated with the denser microstructure of high-pressure-grown μc-Si:H is responsible for the excellent charge collection in p-i-n solar cells.
Materials and Interface Optimization of Heterojunction Silicon (HIT) Solar Cells Using in-situ Real-Time Spectroscopic Ellipsometry
Authors: Levi D.H. , Teplin C.W. , Iwaniczko E. , Ahrenkiel R.K. , Branz H.M. , Page M.R. , Yan Y. , Wang Q. , Wang T.H. 
Published: April 2011

ABSTRACTWe have applied real-time spectroscopic ellipsometry (RTSE) as both an in-situ diagnostic and post-growth analysis tool for hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction with intrinsic thin-layer (HIT) solar cells grown by hot-wire chemical vapor deposition. RTSE enables precise thickness control of the 5 to 25 nm layers used in these devices, as well as monitoring crystallinity and surface roughness in real time. Utilizing RTSE feedback, but without extensive optimization, we have achieved a photovoltaic energy conversion efficiency of 14.1% on an Al-backed p-type Czochralski c-Si wafer coated with thin i and n layers on the front. Open-circuit voltages above 620 mV indicate effective passivation of the c-Si surface by the a-Si:H intrinsic layer. Lifetime measurements using resonant coupled photoconductive decay indicate that surface recombination velocities can approach 1 cm/s. RTSE and transmission electron microscopy show that the intrinsic a-Si:H i-layers grow as a mixture of amorphous and nano-crystalline silicon.
Unexpected Mode of Plastic Deformation in Cu Damascene Lines Undergoing Electromigration
Authors: Budiman Arief S. , Tamura N. , Valek B. C. , Gadre K. , Maiz J. , Spolenak R. , Caldwell W. A. , Nix W. D. , Patel J. R. 
Published: April 2011

AbstractAn unexpected mode of plastic deformation was observed in damascene Cu interconnect test structure during an in-situ electromigration experiment and before the onset of visible microstructural damages (void, hillock formation). We show here, using a synchrotron technique of white beam X-ray microdiffraction, that the extent of this electromigration-induced plasticity is dependent on the line width. The grain texture of the line might also play an important role. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. This early stage behavior can have a direct bearing on the final failure stage of electromigration.
Organic Thin-Film Transistors Fabricated with Alignment-Free Printing Technique
Authors: Ando Masahiko , Kawasaki Masahiro , Imazeki Shuji , Sasaki Hiroshi , Kamata Toshihide 
Published: April 2011

AbstractA novel process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process exploits a self-assembly phenomenon in which soluble nanomaterials such as metal nanoparticles and organic molecules are self-assembled into a device structure. To demonstrate this process, solution-processed source and drain electrodes were self-aligned to a gate electrode by using a hydrophobic self-assembled monolayer (SAM) optically patterned onto the gate electrode with a back-substrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. A field-effect mobility of 0.15 cm2/Vs and on/off current ratio of 105 were experimentally demonstrated when pentacene molecules were used as the semiconductor and silver nanoparticles were used as electrode materials.
Slip Transfer across Hetero-Interfaces in two-phase Titanium Aluminum Intermetallics
Authors: Wiezorek Jörg M.K. , Zhang Xiao-Dong , Fraser Hamish L. 
Published: April 2011

AbstractThe role of slip transfer processes across the heterophase interfaces in two-phase TiAl intermetallics has been studied. Polysynthetically twinned crystals of TiAl (PST-TiAl) have been used as model systems for individual grains in technologically relevant polycrystalline lamellar TiAl alloys. Compressive plastic loads have been applied for orientations of the lamellar interfaces parallel and perpendicular to the loading directions to produce hard mode slip activity. Transmission electron microscopy has been used to determine the active deformation modes in the constituent phases and to study the slip transfer across heterophase interfaces. The results are discussed with respect to the mechanical behavior of PST-TiAl and lamellar TiAl alloys, which is of relevance to in-service performance and metallurgical processing operations.
Grain Boundary Mechanics – Influence of Mechanical Stress Fields on Grain Boundaries
Authors: Winning Myrjam 
Published: April 2011

AbstractThe reaction of grain boundaries to mechanical stresses is reviewed. Results of in-situ experiments on planar, symmetric tilt grain boundaries with different tilt axes (<112>, <111> and <100>) as well as twist grain boundaries with <100> rotation axis will be presented. It was found that the motion of planar grain boundaries can be induced by an imposed external stress irrespective of the angle of misorientation i.e. irrespective whether the grain boundary was a low or high angle grain boundary. The observed activation enthalpies of the stress induced grain boundary motion allow conclusions on the migration mechanism. The motion of planar low and high angle grain boundaries under the influence of a mechanical stress field can be attributed to the movement of the grain boundary dislocations which comprise the structure of the boundary. A sharp transition between low and high angle grain boundaries was observed for different tilt axes. The fact that boundaries can also be moved by mechanical forces sheds new light on microstructure evolution during elevated temperature deformation.
Nickel Silicide Work Function Tuning Study In Metal-Gate CMOS Applications
Authors: Yuan Jun , Pan Grant Z. , Chao Yu-Lin , Woo Jason C.S. 
Published: April 2011

ABSTRACTMid-gap work function (∼4.7eV) for mono-nickel-silicide (NiSi) was obtained by extrapolating flat band voltages of metal-oxide-semiconductor (MOS) capacitors with different gate oxide thickness. Both silicidation temperature and time can affect the nickel silicide work function as a result of different Ni:Si ratio close to the gate oxide interface. Arsenic implantation into the polysilicon before silicidation can shift the NiSi work function towards the silicon conduction band, which makes it suitable for high performance NMOS applications. The physical mechanism responsible for this work function shift is arsenic pile-up at the oxide interface during the nickel silicidation process. Therefore, dual work function metal gate can be obtained by using a single gate full silicidation process. Silicidation temperature and time also affect the work function shift from arsenic dopant, and the incomplete gate silicidation can have the maximum work function modification effect. Arsenic activation temperature before silicidation was found to have a significant effect on the work function shift. Un-annealed samples exhibit a minimum shift in work function due to the low dopant pile-up concentration at the oxide interface.
Composition Dependence of the Judd-Ofelt Intensity Parameters in TeO2-PbF2: Tm3+ Glasses
Authors: Kabalci Idris , Ozen Gonul , Kurt Adnan , Sennaroglu Alphan 
Published: April 2011

ABSTRACTTm3+ -doped glasses with the composition of (1-x)TeO2-xPbF2, where x=10, 15, 20, 25 mol.% were synthesized and, their thermal and absorption measurements were investigated. All the glasses were transparent. The absorption bands corresponding to the absorption of the 1G4, 3F2, 3F3, 3F4, 3H5, and 3H4 levels from the 3H6 ground level of the Tm3+ ion were observed in the optical UV/VIS/NIR absorption measurements. We calculated the integrated absorption cross sections of each band except that of 3H5 level was found to vary with composition of the PbF2. The absorption measurements were first made to determine the spontaneous emission probabilities of the 4f-4f transitions of the Tm3+ ions. The calculations were made by using the Judd - Ofelt theory. The Ω2 parameter shows the strongest dependence on the host composition and it increases with the increasing PbF2 amount. The values Ω4 increases rather slowly while the value of Ω6 is practically independent of the composition. The strong dependence of the parameter Ω2 indicates that this parameter is related to the structural change and symmetry of the local environment of the Tm3+ ions in this glass.
Preparation of Carbon Nano-Materials Using Arc Discharge in Liquid
Authors: Suda Y. , Kawasaki H. , Ohshima T. , Nakashima S. , Kawazoe S. , Toma T. 
Published: April 2011

ABSTRACTCarbon nanomaterials have been prepared using a simple production method of pulsed arc discharge between pure graphite electrodes in liquid. High-resolution transmission electron microscopy observation revealed that two kinds of nanomaterials can be produced in liquid. One of them is powdery products floating on the water surface, and another one is bulky deposits sank down in the water bottom. Some of them have multi-walled carbon nanofibers. Mean diameter of the nanofibers was approximately 30 nm. Optical emission of C+(426.7nm), Hα(656.3nm), Hβ(486.1nm), Hγ(434.0nm), C2 swan bands and CO(457.1nm) can be observed in the arc discharge by using photonic multichannel spectral analyzer. These results indicate that the carbon nanomaterials have been produced by pulsed arc discharge in liquid.
Ab-Initio Calculations for the Electronic Spectra of Cubic and Hexagonal Boron Nitride
Authors: Satta Guido , Cappellini Giancarlo , Olevano Valerio , Reining Lucia 
Published: April 2011

ABSTRACTWe present state of the art fist-principles calculations for the optical spectra and the loss functions of bulk boron nitride in the cubic (c-BN) and in the hexagonal (h-BN) phases. We start from a DFT-LDA density functional Khon-Sham bandstructure to investigate the influence of many-body effects beyond the Random Phase Approximation (RPA) on the optical spectra through the inclusion of self-energy and excitonic effects by a GW calculation and the solution of the Bethe-Salpeter equation. For the loss function we only perform RPA calculations. We show to which extent the description of many-body effects is important for a meaningiful comparison with experiment, and when they can be neglected.
Site-specific formation of nanoporous silicon on micro-fabricated silicon surfaces
Authors: Ou Fung Suong , Saraf Laxmikant V. , Baer Donald R. 
Published: April 2011

ABSTRACTWe demonstrated an ability to control the location of the porous silicon formation during electro-chemical etching by the introduction of micro- fabricated defects. This ability may open new doors for chemical and biological applications of porous silicon. In this paper, we have focused on the experimental procedure used to form this site-specific porous silicon area on micro- fabricated silicon surface. We also compared our results with work carried out by Saraf et al[1] during the early stage of porous silicon formation in conventional electrochemical etching.
Optical properties of CdSe and CdTe nanoparticles embedded in SiO2 films
Authors: Babu Dayal P. , Mehta B. R. , Paulson P. D. 
Published: April 2011

ABSTRACTCdSe and CdTe nanoparticles dispersed in silicon dioxide films have been grown by magnetron sputtering technique followed by thermal annealing. Effect of thermal annealing conditions on the structural and optical properties of CdTe and CdSe nanoparticles has been studied. Glancing angle x-ray diffraction (GAXRD), optical absorption (OA), transmission electron microscope (TEM) and spectroscopic ellipsometry (SE) techniques have been used to study the crystal structure, particle size and dielectric function spectra of nanoparticles. ε2 spectra of CdTe nanoparticles show a decrease in dielectric constant values in comparison to bulk CdTe. ε2″ spectrum of CdTe nanoparticles show four critical points in the electronic band structure of CdTe. Optical absorption studies in the case of CdTe and CdSe nanoparticles clearly show the blue shift of fundamental absorption edge due to quantum confinement effect.
Self-oriented Growth of GaN Films on Molten Gallium
Authors: Li Hongwei , Chandrasekaran Hari , Sunkara Mahendra K , Collazo Ramon , Sitar Zlatko , Stukowski Michael , Rajan Krishna 
Published: April 2011

ABSTRACTThis paper presents a concept of growing near single crystal quality GaN films over large areas through self-oriented growth of GaN platelets on molten gallium. The experiments were performed by nitridation of Ga films on amorphous quartz substrates using nitrogen plasma at low pressures of few mTorr. XRD texture analysis of the free standing GaN flakes with areas over 25 mm2 exhibited an overall c-axis tilt of 2.2°, while showing primary reflections from (0002) and (0004) planes. Further more, the cross-sectional TEM micrographs showed that the resulting GaN films are free from dislocation crops inside the grains but showed diffraction contrast due to small misorientation between the grains. The twist and tilt angles between adjacent columnar grains were determined using convergent beam electron diffraction technique to be less than 8° and 1°, respectively. HRTEM micrographs of the grain boundaries showed sharp interfaces with both twisted and perfect attachments.
Scanning Electron Microscopy Cathodoluminescence Studies of Piezoelectric Fields in an InGaN Multiple Quantum Well Light Emitting Diode
Authors: Bunker Kristin L. , Garcia Roberto , Russell Phillip E. 
Published: April 2011

ABSTRACTScanning Electron Microscopy (SEM)-based Cathodoluminescence (CL) experiments were used to study the influence of piezoelectric fields on the optical and electrical properties of a commercial InGaN-based Multiple Quantum Well (MQW) Light Emitting Diode (LED). The existence and direction of a piezoelectric field in the InGaN-based LED was determined with voltage dependent SEM-CL experiments. The CL emission peak showed a blueshift followed by a redshift with increasing reverse bias due to the full compensation of the piezoelectric field. It was determined that the piezoelectric field points in the [000–1] direction and the magnitude was estimated to be approximately 1.0±0.2 MV/cm. SEM-CL carrier generation density variation and electroluminescence experiments were used to confirm the existence of a piezoelectric field in the InGaN-based MQW LED.
Optical Properties of II-IV-N2 Semiconductors
Authors: Muth John , Cai Ailing , Osinsky Andrei , Everitt Henry , Cook Ben , Avrutsky Ivan 
Published: April 2011

ABSTRACTRecently, wide band gap II-IV-N2 semiconductors such as ZnSiN2, and ZnGeN2 and ZnSiGeN2 have been synthesized, but very little is known about their band structure, optical properties, or electronic properties. Bulk crystals are hard to synthesize because high temperatures and pressures are required. The success in growing II-IV-N2 films epitaxially by MOCVD creates interesting opportunities. The crystal structure of II-IV-N2 compounds is orthorhombic, and when grown on r-plane sapphire can provide a suitable template for GaN growth. Optical transmission studies of the band edge of ZnSiN2 and ZnSiGeN2 with varying Si and Ge percentages were conducted. The indirect nature of the band gap was investigated, and prism coupling was used to obtain the refractive indices in the visible and NIR portion of the spectrum. Although the crystal symmetry was orthorhombic, the refractive indices indicated uniaxial optical properties. Optical loss measurements indicate that the films are suitable for waveguides and novel devices based on birefringent optical effects.
Characterization of the carrier confinement for InGaN/GaN light emitting diode with multiquantum barriers
Authors: Wang Jen-Cheng , Lin Chung-Han , Lin Ray-Ming , Nee Tzer-En , Fang Bor-Ren , Wang Ruey-Yu 
Published: April 2011

ABSTRACTElectroluminescence (EL) of InGaN/GaN multiquantum wells (MQW) in blue light-emitting diodes (LED) with multiquantum barriers (MQB) has been investigated. It was found that a device with an MQB structure exhibited better performance in carrier confinement, as well as higher temperature insensitivity, compared with the conventional MQW LEDs. The total cross sections ware obtained for those devices with and without MQBs, by fitting to the measurement of the spectral intensity. Not only the cross sections, but also the carrier lifetimes depending on temperature can therefore be mainly attributed to changes in Boltzmann population. All the detailed calculations are also agreement with the observations.
The composition dependence of the optical properties of InN-rich InGaN grown by MBE
Authors: Martin R.W. , Edwards P.R. , Hernandez S. , Wang K. , Fernandez-Torrente I. , Kurouchi M. , Nanishi Y. , O'Donnell K.P. 
Published: April 2011

ABSTRACTStudy of the relationship between the composition and optical energies of InxGa1-xN has generated much interest and intrigue over the last decade and beyond. In this paper we describe data from InxGa1-xN epilayers covering the full range of composition (0 < × < 1), grown by both Metal-Organic Vapour Phase Epitaxy (MOVPE) and Molecular Beam Epitaxy (MBE). In particular we concentrate on a set of state-of-the-art InN rich MBE layers (0.6 < × < 1.0). Wavelength dispersive X-ray microanalysis is employed for accurate measurement of the InN fraction and of the group III : group V ratio. The InN rich layers are shown to be highly stoichiometric. The composition results are correlated with luminescence spectra, which show peaks covering the range 1.3 to 0.7 eV. Inclusion of our data from sets of MOVPE and MBE epilayers with InN fractions up to 0.4, measured using identical techniques, allows the composition dependence of the luminescence peak energy to be plotted across the entire composition range. A quadratic fit gives good agreement with both the low-InN MOVPE and high-InN MBE samples but not for the intermediate region. Possible reasons for this are discussed.
AlGaN/GaN Field Effect Schottky Barrier Diode for a Low Loss Switching Device
Authors: Yoshida Seikoh , Ikeda Nariaki , Li Jiang , Hataya Kohji , Wada Takahiro , Takehara Hironari 
Published: April 2011

ABSTRUCT:We have proposed a novel field effect Schottky barrier diode (FESBD) with a dual Schottky structure combined with an AlGaN/GaN heterostructure in order to obtain a very low on-voltage. This diode has a dual Schottky structure of a very low Schottky barrier metal and a high Schottky barrier metal for obtaining a low on-voltage. The leakage current at a reverse bias was suppressed by the pinch-off based on field effect of a higher Schottky barrier metal, resulting in increasing the reverse breakdown voltage.In this paper, we carried out a planer-type FESBD for a large current operation. The AlGaN/GaN heterostructure was grown by a metalorganic chemical vapor deposition (MOCVD). A dual Schottky structure was fabricated using Ti/Al and Pt. An ohmic electrode was also Ti/Al. As a result, the on voltage of FESBD was below 0.1 V. The reverse breakdown voltage was also over 400 V by pinch-off effect. The switching time of the diode was shorter than 3 ns.
High pressure annealing of HVPE GaN free-standing films: redistribution of defects and stress
Authors: Paskova T. , Suski T. , Bockowski M. , Paskov P.P. , Darakchieva V. , Monemar B. , Tuomisto F. , Saarinen K. , Ashkenov N. , Schubert M. , Roder C. , Hommel D. 
Published: April 2011

ABSTRACTThe effect of high temperature, high pressure annealing on morphology, optical and structural properties of free-standing GaN films grown by hydride vapor phase epitaxy is studied. The annealing is found to change the intensities of the photoluminescence peaks as a result of a redistribution of the impurities and native defects in the thick GaN films. A positron annihilation study shows a decrease of the Ga vacancy-related defects below the detection limit after the annealing. The defect redistribution is correlated with a flattening of the stress distribution across the thickness, as revealed by micro Raman study, and with a decrease of the curvature of the annealed free-standing films.