bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indirect Diffusion Mechanism of Boron Atoms in Crystalline and Amorphous Silicon
Authors: Mirabella Salvo , De Salvador Davide , Napolitani Enrico , Bruno Elena , Impellizzeri Giuliana , Bisognin Gabriele , Pecora Emanuele Francesco , Carnera Alberto , Priolo Francesco 
Published: April 2011

ABSTRACTThe diffusion of B atoms in crystalline and amorphous Si has been experimentally investigated and modeled, evidencing the indirect mechanism of these mass transport phenomena. The migration of B occurs after interaction with self-interstitials in crystalline Si (c-Si) or with dangling bonds in amorphous Si (a-Si). In the first case, an accurate experimental design and a proper modeling allowed to determine the microscopic diffusion parameters as the B-defect interaction rate, the reaction paths leading to the diffusing species and its migration length. Moreover, by changing the Fermi level position, B atoms are shown to interact preferentially with neutral or doubly positively charged self-interstitials. As far as the amorphous case is concerned, B diffusion is revealed to have a marked transient character and to depend on the B concentration itself. In particular, boron atoms can move after the interaction with dangling bonds whose density is transiently increased after ion implantation or permanently enhanced by the presence of boron atoms themselves. Unexpectedly, B diffusivity in a-Si is seen to be orders of magnitude above than in c-Si and to depend on the thermal history, i.e. the relaxation status of the amorphous phase. These data are presented and their implications discussed.
Effect of Elevated Implant Temperature on Amorphization and Activation in As-implanted Silicon-on-insulator Layers
Authors: Saenger Katherine L. , Bedell Stephen W. , Copel Matthew , Majumdar Amlan , Ott John A. , de Souza Joel P. , Koester Steven J. , Wall Donald R. , Sadana Devendra K. 
Published: April 2011

ABSTRACTThe ion implantation steps used in fabricating field effect transistors in ultrathin (6 to 30 nm) silicon-on-insulator (UTSOI) substrates present many challenges. Deep source/drain (S/D) implants in UTSOI layers are a particular concern, since it can be difficult to implant the desired dose without amorphizing the entire SOI thickness. In a first study, we investigated the effect of implant temperature (20 to 300 °C) on the sheet resistance (Rs) of 28 nm thick SOI layers implanted with As+ at an energy of 50 keV and a dose of 3 × 1015 /cm2, and found Rs values after activation sharply lower for samples implanted at the highest temperature. In a second study, on 8 nm thick SOI layers implanted with As+ at an energy of 0.75 keV and doses in the range 0.5 to 2 × 1015/cm2, the benefits of the elevated implantation temperature were less clear. Explanations for these effects, supported by microscopy, medium energy ion scattering (MEIS), and optical reflectance data, will be discussed.
First Principles Study of Boron in Amorphous Silicon
Authors: Santos Iván , Windl Wolfgang , Pelaz Lourdes , Marqués Luis Alberto 
Published: April 2011

ABSTRACTWe have carried out an ab initio simulation study of boron in amorphous silicon. In order to understand the possible structural environments of B atoms, we have studied substitutional-like (replacing one Si atom in the amorphous cell by a B atom) and interstitial-like (adding a B atom into an interstitial space) initial configurations. We have evaluated the Fermi-level dependent formation energy of the neutral and charged (±1) configurations and the chemical potential for the neutral ones. For the interstitial-like boron atom, we have find an averaged formation energy of 1.5 eV. For the substitutional case, we have found a dependence of the chemical potential on the distance to Si neighbors, which does not appear for the interstitial ones. From MD simulations, we could observe a diffusion event for an interstitial-like boron atom with a migration barrier of 0.6 eV.
Modeling Evolution of Temperature, Stress, Defects, and Dopant Diffusion in Silicon During Spike and Millisecond Annealing
Authors: Moroz Victor , Martin-Bragado Ignacio , Zographos Nikolas , Matveev Dmitri , Zechner Christoph , Choi Munkang 
Published: April 2011

ABSTRACTThe bulk CMOS devices continue as the dominant player for at least another couple of technology nodes. This drives the increasingly contradicting requirements for the channel, source/drain extension, and heavily doped source/drain doping profiles. To analyze and optimize the transistors, it is becoming necessary to combine a number of effects that have been treated as decoupled so far. The temperature gradients, combined with stress engineering techniques such as embedded SiGe and Si:C source/drain and stress memorization technique, create non-uniform stress distributions determined by the layout patterns. The interaction of implant-induced damage with dopants, stress, and defect traps shapes up the dopant activation, retention of useful stress, and junction leakage. This work reviews recent trends in modeling these effects using continuum and kinetic Monte Carlo methods.
F+ implants in crystalline Si: the Si interstitial contribution
Authors: Lopez Pedro , Pelaz Lourdes , Duffy Ray , Meunier-Beillard P. , Roozeboom F. , van der Tak K. , Breimer P. , van Berkum J. G. M. , Verheijen M. A. , Kaiser M. 
Published: April 2011

ABSTRACTIn this work the Si interstitial contribution of F+ implants in crystalline Si is quantified by the analysis of extended defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that approximately 0.4-0.5 Si interstitials are generated per implanted F+ ion, which is in good agreement with the value resulting from the net separation of Frenkel pairs obtained from MARLOWE simulations. The damage created by F+ implants in crystalline Si may explain the presence of extended defects in F-enriched samples and the evolution of B profiles during annealing. For short anneals, B diffusion is reduced when F+ is co-implanted with Si+ compared to the sample only implanted with Si+, due to the formation of more stable defects that set a lower Si interstitial supersaturation. For longer anneals, when defects have dissolved and TED is complete, B diffusion is higher because the additional damage created by the F+ implant has contributed to enhance B diffusion.
Computer Simulation of the Phase-change Cycle of GST-225
Authors: Elliott Stephen , Hegedus Jozsef 
Published: April 2011

ABSTRACTWe have simulated for the first time, by ab initio molecular dynamics, the complete phase-transformation cycle (liquid-crystal, liquid-amorphous-crystal) of the phase-change (PC) memory material Ge2Sb2Te5 (GST-225). We have observed that rapid cooling of the simulated melt leads to an amorphous product, whereas slow cooling results in the metastable rocksalt crystal. Furthermore, crystallization to the same structure is observed to occur on annealing the quenched amorphous model to temperatures below the melting temperature. The RDF of the energy-relaxed amorphous GST-225 structure agrees very well with experimental neutron-diffraction data, reproducing the shortening of the Ge-Te bond length relative to that in the rocksalt crystal structure observed experimentally.We have observed crystal-nucleation events in the simulated liquid that have been identified as the creation of connected near-regular square fourfold rings, the basic structural units of the rocksalt structure. These crystal nuclei are invariably found to be quenched into the amorphous state on rapid cooling of the simulated melt. This observation therefore explains why GST materials crystallize so readily and why homogeneous nucleation is so facile.
Crystal Growth Rates in Doped SbxTe Fast-Growth Phase-Change Films Studied with Transmission Electron Microscopy
Authors: Kooi Bart J. , Pandian Ramanathaswamy , De Hosson Jeff Th. M. 
Published: April 2011

ABSTRACTIsothermal crystallization of doped SbxTe fast-growth phase-change films was investigated using transmission electron microscopy with in situ heating. SbxTe films with four different values for the Sb/Te ratio, x=3.0, 3.3, 3.6 and 4.2, were analyzed and the films were sandwiched between two types of dielectric layers. One dielectric layer type is based on 80at.%ZnS-20at.%SiO2, the other on (Ge,Cr)N. The crystal growth rates reduce if the phase-change films are sandwiched between amorphous dielectric layers. The reduction is very pronounced at the lowest measured temperatures (150 °C), becomes smaller at higher temperatures and probably disappears at around 200 °C. The crystal growth rates increase with increasing Sb/Te ratio, but the activation energy for crystal growth is not significantly affected by the Sb/Te ratio. Finally a systematic study of the effect of the electron beam of the TEM on the crystal growth rates is performed showing accelerated growth rates. The present work shows that particularly at relative low temperatures, just above the glass-transition temperature, the growth rates as limited by the atomic mobilities are sensitive to various (boundary) conditions, e.g. capping layers and irradiation.
SET Characteristics of Phase Change Bridge Devices
Authors: Krebs Daniel , Raoux Simone , Rettner Charles T. , Shelby Robert M. , Burr Geoffrey W. , Wuttig Matthias 
Published: April 2011

ABSTRACTScaling studies have demonstrated that Phase Change Random Access Memory (PCRAM) is one of the most promising candidates for future non-volatile memory applications. The search for suitable phase change materials with optimized properties is therefore actively pursuit. In this paper, SET (crystallization) characteristics of an ultra fast switching material Ge15Sb85 in phase change memory bridge cell devices are presented. It was found that reproducible switching between two stable states with one decade resistance contrast and current pulses as short as 10 ns for SET and RESET (re-amorphization) operation is possible. Particular emphasis was placed on the difference in crystallization kinetics between the as-deposited and melt-quenched amorphous phase. Evidence is given for the existence of an electrical field as the critical parameter for threshold switching rather than a threshold voltage. For Ge15Sb85 a threshold switching field of 9MV/m was measured and it was shown that switching from the melt-quenched amorphous phase to the crystalline phase is about 600 times faster than crystallization from the as-deposited amorphous phase.
Investigation of SET and RESET States Resistance in Ohmic Regime for Phase-Change Memory
Authors: Savransky Semyon D. , Karpov Ilya V 
Published: April 2011

ABSTRACTNew technique to separate bulk and interface electrical properties of polycrystalline and glassy Ge2Sb2Te5 (GST) in phase-change memory (PCM) devices is proposed. PCM with different GST thicknesses are measured. The average activation energies for bulk conductivity are 0.37 eV and 0.09 eV as well as bulk resistivities are about μOhm*cm2 and 20 μOhm*cm. The contact barriers is 0.07eV and specific contact resistance is about 0.3 μOhm*cm2 in studied PCM devices.It is discovered that bulk resistivities for both SET and RESET states in PCM obey Meyer-Neldel rule with almost identical isokinetic temperatures 335K − 340K. This information is discussed in terms of GST structure.
Atomic Layer Deposition of HfO2 Thin Films on Si and GaAs Substrates
Authors: Hackley Justin C , Demaree J. Derek , Gougousi Theodosia 
Published: April 2011

ABSTRACTThe atomic layer deposition of HfO2 thin films is studied on Si(100) and GaAs(100) surfaces. The films are grown using tetrakis(dimethylamido)hafnium (TDMAH) and H2O precursors at a deposition temperature of 275°C. The Si surfaces used include a H-terminated surface and an OH-rich chemical oxide. GaAs substrates are subjected to two different pre-deposition treatments involving an HF and a NH4OH wet chemical etch that has been shown to remove most of the Ga and As native oxides. Spectroscopic ellipsometry (SE) confirms linear growth rates of 1.05±0.05 Å/cycle for all surfaces. Rutherford backscattering spectrometry (RBS) shows that steady-state growth of 2.6×1014 Hf/cm2/cycle is reached after 10 ALD cycles for the HF-etched GaAs surface. X-ray photoelectron spectroscopy (XPS) indicates the presence of native oxides on both GaAs starting surfaces after 10 cycles due to postdeposition surface oxidation. However, the presence of the native oxide is not detected for thicker 15 and 20 cycle samples indicating passivation of the surface and suppression of the interfacial layer formation.
Physical origin of colossal dielectric constant in CaCu3Ti4O12 thin film by Pulsed Laser Deposition
Authors: Deng Guochu , Yamada Tomoaki , Muralt Paul 
Published: April 2011

ABSTRACTThe (001) preferentially oriented CCTO thin film was grown on Pt/Ti/TiO2/Si (100) substrate by pulsed laser. I-V and C-V relationships of the CCTO thin film showed characteristics typical of a tunnel metal-insulator-semiconductor (MIS) structure and its capacitance response is the origin of the high apparent dielectric constant observed in CCTO thin films. The very thin insulating layer on top of the film can be reduced in thickness by treatment in HCl acid, as shown by smaller threshold voltages in the I-V curves. The overall behavior is compatible with a conduction activation energy of ∼80 to 100 meV in the bulk of the film, and a diffusion potential at the interface of 500 to 800 meV. The acceptor concentration is of the order of 1019cm−3.
Optical Detection of SiN Stress Layer Induced Carrier Mobility Enhancement in Silicon
Authors: Wirbeleit Frank , Pedrero Victoria , Thron Dominik , Stephan Rolf , Schwalke Udo 
Published: April 2011

ABSTRACTStrain engineering is key element for improving MOSFET device performance in today's advanced high performance microelectronics. Strained SiN layers are well established in this regard to generate near surface strain effects for carrier mobility enhancement. Non destructive detection of effects from strain layers has not been resolved yet, especially during the processing of patterned wafers. Since optical reflective measurements are well established for non destructive thickness measurements in semiconductor manufacturing, the signals out of those spectra can be used to investigate stress induced carrier mobility enhancement effects, as shown in this work. This provides direct access to the effectiveness of the applied near surface strain to the carrier mobility. By this novel method, SiN films at different stress levels and under different process conditions are investigated on silicon bulk wafers. On these wafers, the optically detected spectra shift, known as plasmon shift, can be correlated with standard wafer bow stress measurement results. These results are correlated to the electrical performance of microelectronic test structures. Based on this, the relative variation of the stress levels of SiN films after different process treatments, and the impact on carrier mobility in microelectronic devices is shown.
MeV Si Ions Bombardment Effects on the Properties of Nano-Layers of SiO2/SiO2+Ag
Authors: Guner Sadik , Budak Satilmis , Muntele Claudiu I , Smith Cydale C , Ila Daryush 
Published: April 2011

ABSTRACTWe have grown 100 periodic SiO2/SiO2+Ag multi-nano-layered systems where the SiO2+Ag layers were 7.26 nm and SiO2 buffer layer were 4 nm, total thickness is 563 nm. Using interferometer as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The electrical conductivity measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the figure of merit as a function of the bombardment fluence.
Is Transition Metal Incorporated ZnO an Intrinsic Ferromagnetic Semiconductor?
Authors: Bhatti Kanwal P , Chaudhary Sujeet , Pandya Dinesh K , Kashyap Subhash C 
Published: April 2011

ABSTRACTStudies on Mn, Ni and Co doped ZnO systems have revealed that the RTFM present in these systems can be both intrinsic and extrinsic depending on the choice of TM ion incorporated, technique of preparation and post-synthesis processing. Choice of such a technique that ensures better homogeneity and incorporation of TM ions in the ZnO host, leads to the occurrence of intrinsic, stable and robust RTFM. The air ambient processing eliminates the chances of any metallic cluster inclusions, and instead such TM oxide phases are formed that are non-ferromagnetic. However, post synthesis processing like vacuum annealing of ZnO:Co samples under some situations can give rise to occurrence of extrinsic RTFM. But, this can be overcome by certain additional processing step. ZnO:Co samples with intrinsic RTFM, stable upto 900°C annealing with Curie temperatures in excess of 450°C have successfully been prepared.
Transparent Oxide Semiconductors Obtained by PLD
Authors: Vila Anna , Olziersky Antonis , Font Joaquim , Andreu Teresa , Koep Erik , Morante Juan Ramon 
Published: April 2011

ABSTRACTIn this work we studied metaloxide films such as ZnO, In2O3-ZnO, In2O3-ZnO-ZrO2 and Ga2O3-In2O3-ZnO deposited by pulsed laser deposition on fused silica substrates at room temperature. Optical transmission measurements in the ultra violet – visible region showed that oxygen-rich atmospheres during deposition help to obtain more transparent films in the optical region while improving overall UV absorption transition related to the band gap. Less resistive films are produced in oxygen-rich atmospheres but an increase of oxygen pressure leads to higher resistivity films.
X-ray Absorption Spectroscopy Investigation of Different Crystallographic Structures of Cobalt Nanoparticles
Authors: Palshin Vadim , DeSilva Rohini , Kumar Challa SSR 
Published: April 2011

ABSTRACTThe ultimate goal of nanotechnology is to design successful syntheses to produce nanomaterials with required properties. The properties of nanoparticles mainly depend on their size, shape and crystal structure, hence control over these factors is a major issue in this field. In this study, Co nanoparticles with four different crystallographic structures (hcp, fcc, bcc and epsilon) have been wet-chemically synthesized by varying precursors and surfactants in the reaction. Co K-edge absorption spectra were collected in transmission mode at the XMP beamline at the Center for Advanced Microstructures and Devices (CAMD). The X-ray Absorption Near Edge Structure (XANES) and Fourier Transformed Extended X-ray Absorption Fine Structure (FT EXAFS) spectra were analyzed using the “fingerprint method”, i.e. by comparing them with either standard compounds or with the simulated spectra that were calculated using the FEFF8 code. EXAFS spectra were also analyzed by fitting them with relevant crystallographic models in r-space including higher coordination shells using the IFEFFIT analysis program. All four crystal structure types were conclusively determined by using this approach.
A Modified Chemical Route for Synthesis of Zirconia Thin Films Having Tunable Porosity
Authors: Kumar Manish , Reddy G. B. 
Published: April 2011

ABSTRACTA new chemical synthesis route is reported for deposition of zirconia thin films having adjustable porosity with average pore size in nanometer range. Deposition method is simply a sol-gel dip coating in which HCl is used as catalyst. TEM and FTIR studies of deposited films show porous microstructure, which depends critically on ageing of sol used. The shift in binding energy of Zr 3d5/2 (at 182.4 eV) attributes the formation of zirconia. Optical results show high transmittance (> 80%) in VIS-NIR region and effective refractive indices values (neff) tend to decrease for films prepared with higher aged sol. Porosity enhancement from 15-52% is observed by neff comparing with refractive index of non porous films (nz).
Structural and Luminescence Properties of Nanocrystalline Eu3+-doped Gd2O3
Authors: Jauregui Segundo , Perales-Perez Oscar , Vasquez Omar , Jia W. , Tomar M. S. , Fachini Esteban 
Published: April 2011

ABSTRACTThe present work addresses the synthesis and characterization of red emitting Gd2-xEuxO3 nanocrystalline phosphors by a modified sol-gel based method. The effects of the annealing temperature and atomic fraction of Eu3+ ions, ‘x’, on the structural and luminescence properties of the produced oxides have been systematically investigated. X-ray diffraction analyses revealed that crystalline cubic-Gd2O3 host structure was obtained when the intermediates (x=0.01-0.30) were annealed at different temperatures in air. Photoluminescence spectra of doped Gd2O3 powders showed all transitions of Eu3+ species, being the 5D0→7F2 transition the most intense. On a common sample-weight basis, the highest photoluminescence intensity was obtained at ‘x’ = 0.15. The energy transfer from host to dopant was verified for all evaluated ‘x’ values, which suggest the actual incorporation of Eu species into the Gd-oxide lattice. It was also found that the photoluminescence intensity was strongly dependent on the annealing temperature and dopant concentration.
Infrared detector activities at NASA Langley Research Center
Authors: Abedin M. Nurul , Refaat Tamer F , Sulima Oleg V , Amzajerdian Farzin 
Published: April 2011

ABSTRACTInfrared detector development and characterization at NASA Langley Research Center will be reviewed. These detectors were intended for ground, airborne, and space borne remote sensing applications. Discussion will be focused on recently developed single-element infrared detector and future development of near-infrared focal plane arrays (FPA). The FPA will be applied to next generation space-based instruments. These activities are based on phototransistor and avalanche photodiode technologies, which offer high internal gain and relatively low noise-equivalent-power. These novel devices will improve the sensitivity of active remote sensing instruments while eliminating the need for a high power laser transmitter.
Role of Lidar Technology in Future NASA Space Missions
Authors: Amzajerdian Farzin 
Published: April 2011

ABSTRACTThe past success of lidar instruments in space combined with potentials of laser remote sensing techniques in improving measurements traditionally performed by other instrument technologies and in enabling new measurements have expanded the role of lidar technology in future NASA missions. Compared with passive optical and active radar/microwave instruments, lidar systems produce substantially more accurate and precise data without reliance on natural light sources and with much greater spatial resolution. NASA pursues lidar technology not only as science instruments, providing atmospherics and surface topography data of Earth and other solar system bodies, but also as viable guidance and navigation sensors for space vehicles. This paper summarizes the current NASA lidar missions and describes the lidar systems being considered for deployment in space in the near future.
All Fiber Coherent Doppler LIDAR for Wind Sensing
Authors: Ando Toshiyuki , Kameyama Shumpei , Asaka Kimio , Hirano Yoshihito , Tanaka Hisamichi , Inokuchi Hamaki 
Published: April 2011

ABSTRACTAn 1.5 micron pulsed Coherent Doppler LIDAR system using all fiber optical components has attracted attention for remote wind sensing application because of its eye-safety, reliability and easy deployment. We report on our key technologies such as fiber based MOPA (Master Oscillator Power Amplification) transmitter, high peak power optical amplification and a real-time signal processing. Some performance results and applications are also provided.