bluuebunny/crossref_metadata_2025 huggingface dataset:
Power Feeding in Large Area PECVD of Amorphous Silicon
Authors: Kuske J. , Stephan U. , Steinke O. , Röhlecke S.
Published: April 2011

Plasma processes are usually worked out in a small-scale environment (electrode area maximum 121 cm2, rf- and VHF- excitation frequencies). In order to meet the requirements of large area device applications they have to be upscaled. The investigations of glow discharge systems for different PECVD reactors (parallel plate- and coaxial electrodes) have shown, that the reactor design (power supply, line connection) sharply influences the large area deposition process. The voltage distribution on the driven electrode especially determines the uniformity of the deposited layer thickness. Possibilities which influence the voltage distribution on large areas will be discussed. The results of large area electrode description as an electrical line will be discussed in comparison with different reactor configurations and the optimization of the behavior of the deposition process. The experimental results of a coaxial reactor (electrode area 5000 cm2, substrate length 120 cm) show that a homogenous deposition of amorphous silicon (layer uniformity of thickness over the length better ± 7 %) by connecting the driven electrode with additional electrical devices is possible.
Monte Carlo Simulations of Defect Relaxation in Amorphous Silicon
Authors: Unold Thomas , Branz Howard M.
Published: April 2011

The structural memory model of slow defect relaxation in a-Si:H is extended to the limit of long defect filling times. The model was proposed in order to explain unusual, defect filling-time dependent capacitance transients that were observed for short defect filling times. For long defect filling pulses however, the experiments show normal charge emission transients that saturate into filling-time independent transients. We present two possibilities for explaining the approach to saturation within the structural memory model. Results of Monte Carlo simulations of the models are discussed.
Recovery Process of Light-Induced Spins in Hydrogenated Amorphous Silicon-Nitrogen Alloy Films
Authors: Zhang Jinyan , Zhang Qing , Kumeda Minoru , Shimizu Tatsuo
Published: April 2011

The influences of sub-gap illumination and thermal annealing on the light-induced neutral dangling bonds (DB's) created in the fast process (FDB's) and those created in the slow process (SDB's) are prominently different in Si-rich a-Si1-xNx:H. The results of photobleaching show that the sub-gap illumination annihilates FDB's, more effectively at 77 K, whereas it appears not to affect SDB's, suggesting that FDB's are produced by a carrier capture at preexisting charged DB's. The annealing behaviors for both FDB's and SDB's are in agreement with the monomolecular kinetics. The attempt-to-anneal frequency, ν0, is ∼ 103 Hz for FDB's and ∼ 107 Hz for SDB's. Annealing-time dependence of the density of light-induced spins at various annealing temperatures can be fit with a distribution of annealing activation energies. In addition, clearly separated peaks of the distribution of annealing activation energies related to FDB's and SDB's are observed. A comparison indicates that SDB's have a nature similar to the light-induced metastable spins in a-Si:H, which are likely to be produced by a creation of new defects.
Carrier-Induced Changes in The Gap States of Undoped a-Si:H Films
Authors: Chen Y. E. , Tsai J. W. , Cheng H. C.
Published: April 2011

Carrier-induced changes in the gap states of plasma-enhanced-chemical-vapor-deposited (PECVD) undoped a-Si:H films are systematically studied using isothermal capacitance transient spectroscopy (ICTS) method via the novel structure we proposed previously. The density-of-state distribution g (E) and the energy dependence of electron-capture cross section σn (E) of gap states in undoped a-Si:H films before and after injection of electrons are directly measured for the first time. Experimental results show that the density of g (E) increases but the σn (E) has no obvious change after the electron injection. These indicate that the defects created during the electron injection are the same in type as those of the as-deposited films. In addition, it is found the shape of g (E) distorts after the injection, implying that the gap states with different energy levels are associated with distinct types of defects.
Microwave Glow-Discharge Deposition of Amorphous Silicon Based Alloys at High Deposition Rates for Solar Cell Application
Authors: Guha S. , Xu X. , Yang J. , Banerjee A.
Published: April 2011

The optimum deposition conditions for growth of amorphous silicon (a-Si:H) and silicon-germanium (a-SiGe:H) alloys deposited at high rates using microwave glow-discharge are found to be quite different from those for radio-frequency glow-discharge material deposited at low rates. High substrate temperature (350 to 500 °C), low pressure (1–5 mtorr) and positive ion bombardment are found to be desirable for optimum growth conditions at high deposition rates. We have achieved an active-area efficiency of 11.44% for a double-junction structure in which the bottom cell incorporates a-SiGe:H alloy deposited at 100 Å/sec using microwave glow-discharge.
Performance of Photo-Transistors with thin (50 nm.) a-Si:H Layers
Authors: GadelRab Serag M. , Chamberlain Savvas G.
Published: April 2011

Photo-transistor based a-Si:H image sensors allow the integration of photo-elements and pixel circuitry using standard TFT fabrication processes. While pixel circuitry use thin a-Si:H films (≈ 0.05μm) to minimize the contact resistance, photo-transistors require thick a-Si:H films (≈0.5μm) to maximize photo-sensitivity. We fabricated a new, high sensitivity photo-transistor structure using 0.05μ a-Si:H films. High optical sensitivity is achieved by separating the conduction paths of photo-generated electrons and holes using a secondary gate. Further, the optical path within the photo-transistor is doubled through manipulation of device layout. The photo-transistor show an Ilight/Idarkratio in excess of 103.

We compared the transient behavior of conventional and high-sensitivity photo-transistors. We found that both devices display an increase in current with time when biased in either the dark or illuminated conditions. The current increases by six orders of magnitudes then saturates within 200 seconds of bias application. Experiments indicate that this transient behavior is due to a rise in the conductivity of the gap region with time; measurements on 0.05μm thick photo-resistor structures showed that their current increases with time. The shape and temporal range of this behavior rules out the presence of parasitic capacitive effects.
Temperature and Frequency Dependent Characteristics of Amorphous Silicon thin film Transistors
Authors: Slade H. C. , Shur M. S. , Hack M.
Published: April 2011

On the basis of our experimental studies of the temperature dependence of amorphous silicon thin film transistor current-voltage and capacitance-voltage characteristics, we have developed an analytical device model suitable for implementation in circuit simulators. This model describes the above-threshold (on) current and the subthreshold (off) current [1]. In addition, the model is able to incorporate changes in the distribution of localized states which arise from thermal and/or bias stress. In this paper, we identify the temperature-dependent parameters, which describe the temperature dependence of both the on and off currents, and we model the leakage current at large negative gate biases. The modeling results are in good agreement with our experimental data. We also discuss capacitance-voltage characteristics of amorphous silicon thin film transistors for varying gate lengths, temperatures, and frequencies. The measured capacitance-voltage characteristics show strong frequency dispersion, which is related to the trap-limited transport of carriers in the channel. The characteristic time constant, which determines when the channel capacitance becomes dependent on frequency, is on the order of the transit time calculated with the field-effect mobility and the electric field. The field-effect mobility takes into account carrier trapping by the localized states and is a function of gate voltage and temperature.
Utilization of Photoconductive Gain in a-Si:H Devices for Radiation Detection
Authors: Lee H. K. , Drewery J. S. , Hone W. S. , Jing T. , Kaplan S. N. , Perez-Mendez V.
Published: April 2011

The photoconductive gain mechanism in a-Si:H was investigated in connection with applications to radiation detection. Various device types such as p-i-n, n-i-n and n-i-p-i-n structures were fabricated and tested. Photoconductive gain was measured in two time scales: one for short pulses of visible light (< 1 μsec) which simulates the transit of an energetic charged particle, and the other for rather long pulses of light (1 msec) which simulates x-ray exposure in medical imaging. We used two definitions of photoconductive gain: current gain and charge gain which is an integration of the current gain. We found typical charge gains of 3 ∼ 9 for short pulses and a few hundred for long pulses at a dark current level of 10 mA/cm2. Various gain results are discussed in terms of the device structure, applied bias and dark current.
Hyperacuity Image Sensors
Authors: Biegelsen David K. , Jackson Warren B. , Lujan René , Jared David , Weisfield Richard L.
Published: April 2011

The human visual system perceives much smaller spatial steps in edges between high contrast regions than equivalents fine, periodic features. This characteristic is known as hyperacuity. We have designed, simulated, fabricated and characterized amorphous silicon sensors which provide hyperacuity information. The individual pixels are position sensitive detectors, the outputs of which provide the x and y first moments of the cell illumination pattern as well as the average gray level. In the simplest case the top electrode of a standard p-i-n diode sensor is replaced by four edge strip electrodes. Both quadrilateral cells (having all four lateral electrodes on the same side of the p-i-n diode) and duolateral cells (having x-electrodes on top and y-electrodes on bottom) have been tested. Results of probing the cells with rastered spots show that both types provide usable linearity and sensitivity. The duolateral structure provides greater orthogonality of the x and y information. One μm spatial resolution can be achieved with devices compatible with standard amorphous silicon sensor processing.
Numerical Simulation of Point Defect Distributions in a Growing Czochralski Silicon Crystal in Response to an Abrupt Change in the Growth Conditions
Authors: Wijaranakula W. , Zhang Q. S. , Takano K. , Yamagishi H.
Published: April 2011

Numerical simulation of point defect distributions in a growing Czochralski silicon crystal with an abrupt change in the crystal growth rate from 1.0 to 0.4 mm/min was performed. The result was fitted to the experimental data for the flow pattern defects obtained from a crystal grown under simulated conditions. From the simulation result, it was observed that the axial temperature distribution shifts slightly upwards as a result of the growth rate reduction. Based upon the argument that the flow pattern defects are of vacancy-type, it is proposed that the generation rate of the flow pattern defects during crystal growth can be described by the classical nucleation rate theory proposed by Becker [Proc.Phys.Soc., 52, 71(1940)]. In addition, it is suggested that the vacancy concentration in the flow pattern defects depends upon the reaction time between the silicon interstitials and the flow pattern defects and thus the crystal growth rate.
Intentional Defect Incorporation in Metalorganic Vapor Phase Epitaxy Indium Gallium Arsenide by Oxygen Doping
Authors: Huang J. W. , Kuech T. F.
Published: April 2011

Intentional defect incorporation in metalorganic vapor phase epitaxy (MOVPE) InxGai-xAs was achieved by controlled oxygen doping using diethylaluminum ethoxide (DEALO). DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in InxGai-xAs:Si with 0≤x≤ 0.25. DLTS analysis on a series of InxGa1-xAs:Si:O samples with 0≤x≤ 0.18 showed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. The characteristic deep levels appear to remain at a relatively constant energy with respect to the valence band.
Effect of P-Doping Level-POCl3 Diffused or Spin-On Deposited-On the Gettering Efficiency of Polycrystalline Silicon After RTA or CTA
Authors: Loghmarti M. , Mahfoud K. , Muller J. C. , Sayah D. , Siffert P.
Published: April 2011

Large grain polycrystalline silicon wafers have been subjected to post-thermal annealing after a POCl3 pre-diffusion or after a phosphorus doped silica-film deposition (1019p/cm3- 2.1021p/cm3). The different doping levels are obtained by a dilution of the P-doped SOG (2.1021 at/cm3) in a undoped SOG solution .For the first time we have achieved the maximum of the gettering efficiency after post-thermal annealing. The best combination of post thermal cycle parameters and doping level improves the minority carrier diffusion length of quite (300% to 400%) for POCl3 pre-diffused samples and (200% to 275%) for spin-on P-doped (P-SOG) polycrystalline silicon.
The Role of Impurities in Hydride Vapor Phase Epitaxially Grown Gallium Nitride
Authors: Molnar R. J. , Nichols K. B. , Maki P. , Brown E. R. , Melngailis I.
Published: April 2011

Gallium nitride (GaN) films grown by hydride vapor phase epitaxy on a variety of substrates have been investigated to study what role silicon and oxygen impurities play in determining the residual donor levels found in these films. Secondary ion mass spectroscopy analysis has been performed on these films and impurity levels have been normalized to ion implanted calibration standards. While oxygen appears to be a predominate impurity in all of the films, in many of them the sum of silicon and oxygen levels is insufficient to account for the donor concentration determined by Hall measurements. This suggests that either another impurity or a native defect is at least partly responsible for the autodoping of GaN. Additionally, the variation of impurity and carrier concentration with surface orientation and/or nucleation density suggests either a crystallographic or defect-related incorporation mechanism.
Study of Deep Levels by Admittance Spectroscopy in High Resistivity P-Type 6H-SiC Single Crystals
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: April 2011

Deep levels in high resistivity p-type 6H-SiC has been studied using optical admittance spectroscopy ( OAS ). Besides the conductance peak due to the band to band transitions, there are three conductance peaks in the spectra of most of the samples. The conductance peak due to the vanadium donor (0/+) level at EV+ 1.55 eV is identified. The persistent photoconductance (PPC) at this defect was also studied. The decay kinetics of the PPC follow the stretched exponential form. The potential barrier against recapture of carriers was determined to be 220 meV for the vanadium donor level.
Applications of Scanning Defect Mapping System for Semiconductor Characterization
Authors: Carr Kavin F , Carlson N. , Weitzman P. , Sopori B. L. , Marshall C. , Allen L.
Published: April 2011

A laser scanning system has been developed by the National Renewable Energy Laboratory for the rapid characterization of crystal defects in single- and poly-crystalline semiconductors. The scanning defect mapping system has been commercialized by Labsphere, Inc. as the PVScan 5000. In the unprocessed material, the system produces digital color maps of the spatial distributions of dislocations and grain boundaries simultaneously. After device fabrication, the PVScan 5000 is used to produce photoresponsivity maps of the light beam induced current (LBIC) on a photovoltaic device such as a solar cell or a photodetector. An additional feature is that it also measures the spatial distributions of optical reflectance, both specular and diffuse, which can be applied to the LBIC maps to determine the internal responsivity of the device. The internal responsivity is proportional to the minority carrier diffusion length of silicon devices. It may be possible, therefore, to determine the diffusion length for certain devices.
Influence of Electric Field and Temperature on Magnetic Field Induced Prolonged Changes of Electric Parameters of Silicon Systems
Authors: Maslovsky Vladimir M
Published: April 2011

Magnetic field induced prolonged changes (MFIPC) of electric parameters of semiconductor systems is the phenomenon that has been recently established experimentally. In this work it is investigated for the first time the influence of electric field and temperature on duration of MFIPC of carrier generation lifetime in Si subsurface region and the influence of temperature on MFIPC of the MOS structure leakage voltage. The value of determined mobility of generated defects corresponds to the diffusion coefficient of vacancy -impurity complexes. These investigations of MFIPC of microstructure confirm that non-equilibrium defects reactions are limited by diffusion (in the absence of external electric field). It is shown that the corresponding diffusion coefficient is about 10−13 cm2s−1 and the magnitude of diffusion activation energy determined from these investigations is in the range 0.45–0.5 eV. This value is nearly the same as the diffusion coefficient of vacancy-impurity complex.
Influence of Dislocations on the I-V Characteristics of Silicon Solar Cells
Authors: Murphy Robert , Sopori Bhushan L. , Rose Doug
Published: April 2011

This paper presents a phenomenological approach for analysis of dislocations in a large-area device like a solar cell. A microscopic model of a dislocation is used to calculate the local effects of a dislocation on the dark and the illuminated characteristics of a p-n junction device. A statistical approach is then used to empirically arrive at the I-V characteristics of a small-area device with a uniform distribution of dislocations. Finally, these results are applied to develop a network model to determine the terminal characteristics of a large-area solar cell of a known spatial distribution of dislocations. We show that the performance of a solar cell is influenced not only by the density of dislocations but also by their spatial distribution; heavily dislocated regions exert a disproportionately large degradation effect on the device characteristics.
Defects and Impurities in Mercuric Iodide Processing
Authors: Van Scyoc J. M. , James R. B. , Schlesinger T. E. , Gilbert T. S.
Published: April 2011

In the fabrication of mercuric iodide (HgI2) room temperature radiation detectors, as in any semiconductor process, the quality of the final device is very sensitive to the impurities and defects present. Each process step can change the effects of existing defects, reduce the number of defects, or introduce new defects. In HgI2 detectors these defects act as trapping and recombination centers, thereby degrading immediate performance and leading to unstable devices. In this work we characterized some of the defects believed to strongly affect detector operation. Specifically, we studied impurities that are known to be present in typical HgI2 materials. Leakage current measurements were used to study the introduction and characteristics of these impurities, as such experiments reveal the mobile nature of these defects. In particular, we found that copper, which acts as a hole trap, introduces a positively charged center that diffuses and drifts readily in typical device environments. These measurements suggest that Cu, and related impurities like silver, may be one of the leading causes of HgI2 detector failures.
Study of Oxygen Diffusion and Clustering in Silicon Using an Empirical Interatomic Potential
Authors: Jiang Z. , Brown R. A.
Published: April 2011

The diffusion path and diffusivity of oxygen in crystalline silicon are computed using an empirical interatomic potential which was recently developed [1] for modelling the interactions between oxygen and silicon atoms. The diffusion path is determined by constrained energy minimization, and the diffusivity is computed using jump rate theory. The calculated diffusivity D=0.025 exp(-2.43eV/kBT) cm2/sec is in excellent agreement with experimental data. The same interatomic potential also is used to study the formation of small clusters of oxygen atoms in silicon. The structures of these clusters are found by NPT molecular dynamics simulations, and their free energies are calculated by thermodynamic integration. These free energies are used to predict the temperature dependence of the equilibrium partitioning of oxygen atoms into clusters of different sizes. The calculations show that, for given total oxygen concentration, most oxygen atoms are in clusters at temperature below 1300K, and that the average cluster size increases with decreasing temperature. These results are in qualitative agreement with the effects of thermal annealing on oxygen precipitation in silicon crystals.
Recombination at Oxidation Induced Stacking Faults in Silicon
Authors: Davidson J. A. , Evans J. H. , Vandini M. , Peaker A. R.
Published: April 2011

We have characterised the recombination at Oxidation Induced Stacking Faults (OISF) by employing a combination of DLTS and Minority Carrier Transient Spectroscopy (MCTS). The recombination rate at traps associated with the OISF has been compared with recombination at a conventional point defect also present in the silicon. We find that the effect of small amounts of decoration by copper is to increase hole capture rates at electron filled traps. Infra Red Beam Induced Current measurements are consistent with this in that they also indicate that decoration causes enhanced recombination at the extended defects.
Two Dimensional Magnetic Properties of PdFe Layers
Authors: Petroff F. , Cros V. , Fert A. , Lamolle S. , Wiedmann M. , Schuhl A.
Published: April 2011

We have studied the magnetic properties of very thin PdFe films grown by molecular beam epitaxy. The behavior expected for a 2D Heisenberg system - that is a variation of the susceptibility as exp(B/T) and a logarithmic dependence of the magnetization on the applied field - is observed in a certain range of temperature and field. This is in agreement with recent results of Webb et al [1].
Direct Experimental Study of Domain Structure In Magnetic Multilayers
Authors: Nikitenko V.I. , Gornakov V.S. , Dedukh L.M. , Bennett L.H. , McMichael R.D. , Swartzendruber L.J. , Hua S. , Lashmore D.L. , Shapiro A.J.
Published: April 2011

We have applied a polarized light optical microscope in reflective mode with a Bi-substituted yttrium-iron-garnet indicator film with in-plane anisotropy for visualization of the magnetostatic fields produced by nanostructured magnetic CoNiCu/Cu electrodeposited multilayers. By analysis of the magneto-optical stray field image, detailed information is obtained not only on the as-grown multilayer magnetic structure but on its change during the magnetization reversal processes. The influences of crystal lattice defects and nonuniformity of the nonmagnetic spacers thicknesses on the domain wall nucleation and motion are studied. Peculiarities of the re-magnetization of antiferromagnetically exchange coupled multilayers are discussed, including real-time observations of domain wall creep in a constant applied field.
Unified Semi-Classical Theory of Parallel and Perpendicular Giant Magnetoresistance in Superlattices
Authors: Ustinov V.V. , Kravtsov E.A.
Published: April 2011

The giant magnetoresistance in magnetic superlattices for the current perpendicular to and in the layer planes is studied within a unified semi-classical approach that is based on the Boltzman equation with exact boundary conditions for the spin-dependent distribution functions of conduction electrons. We show that the main differences between the in-plane and perpendicular-to-plane magnetoresistance result from the fact that they originate from different interface processes responsible for spin-dependent scattering. A correlation between the giant magnetoresistance and the superlattice magnetization is also discussed and it is shown that its study has much potential for yielding information about properties of spin-dependent scattering in magnetic superlattices.
Second Order Magneto-Optic Effects in Epitaxial FE(110)/MO(110) Bilayers
Authors: Osgood R.M. , White R.L. , Clemens B.M.
Published: April 2011

The signal measured during a Magneto-Optic Kerr Effect (MOKE) experiment is usually assumed to be linear in the magnetization (or the magnitude of the magneto-optic coupling vector Q that is proportional to the magnetization) so that a plot of the magnetization versus applied field can be obtained. We have observed an appreciable contribution from the Q2 term in the magneto-optic response of epitaxial Fe(110)/Mo(110) bilayers. The Q2 term in the magneto-optic response is much larger than that predicted by existing theory. We re-derive and modify the existing theory to fit the Q2 term.
Surface Enhanced Magneto-Optics in Noble Metal / Ferromagnetic Metal Multilayers
Authors: Safarov V. I. , Kosobukin V. A. , Hermann C. , Lampel G. , Peretti J. , MarliÉre C.
Published: April 2011

We present an electromagnetic enhancement mechanism for the magneto-optical response of noble metal / ferromagnetic metal multilayer thin films. When such a structure is illuminated in total reflection condition, the resonant coupling of light with the noble metal surface plasmons gives rise to an amplification of the magneto-optically induced component of the light electric field. The experimental results obtained on a 30nm-thick Au / Co / Au model system show that this resonant feature observed in the Kerr rotation and ellipticity corresponds to a strong enhancement of the magneto-optical figure of merit and signal-to-noise ratio.
Towards the Synthesis of Atomic Scale Wires
Authors: Anderson P. A. , Woodall L. J. , Porch A. , Armstrong A. R. , Hussain I. , Edwards P. P.
Published: April 2011

Recent work1 has highlighted the possibility that through the introduction of metals into the one-dimensional channels of zeolite L, it may be feasible to engineer charge transport along the channels to produce a unique compound comprising a precise, assembled array of ultrafine, atomic-scale conducting wires embedded within the aluminosilicate framework. Using electron spin resonance (ESR), and microwave cavity perturbation measurements, we examine the properties of these remarkable materials as a function of composition as they approach the insulator to metal transition.
Plasma Polymerized Primers for Rubber to Metal Bonding: Characterization of the Interphase
Authors: Tsai Y. M. , Boerio F. J. , Kim Dong K.
Published: April 2011

Plasma polymerized acetylene films contained mono- and di-substituted acetylene groups, aromatic groups, and carbonyl groups which resulted from reaction of residual free radicals with oxygen when the films were exposed to the atmosphere. There was some evidence for formation of acetylides in the interphase between the films and the substrates. Reactions occurring in the interphase between the plasma polymerized films and natural rubber were simulated using a model rubber compound consisting of a mixture of squalene, zinc oxide, carbon black, sulfur, stearic acid, diaryl-p-diphenyleneamine, and N,N-dicyclohexylbenzothiazole sulfenamide (DCBS). Zinc oxide and cobalt naphthenate reacted with stearic acid to form zinc and cobalt stearates. The stearates reacted with the benzothiazole sulfonamide moiety of DCBS and with sulfur to form zinc and cobalt accelerator complexes and perthiomercaptides. The complexes and perthiomercaptides reacted with squalene and the plasma polymer to form pendant groups which eventually disproportionated to form crosslinks between squalene and the primer. Migration of double bonds during reaction of the model rubber compound with the films resulted in formation of conjugated double bonds in squalene.
Sticking Probability and Step Coverage Studies of SiO2 and Polymerized Siloxane Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition
Authors: Theil Jeremy A.
Published: April 2011

This paper describes a method for estimating the effective sticking probability for plasma enhanced chemical vapor deposition (PECVD) of hexamethyldisiloxane (HMDSO) using SiO2 and polymerized siloxanes deposited on specially prepared trench structures. Comparison of the data with direct Monte-Carlo simulation curves provides information about the incorporation probability relative to film growth. It is shown that besides variation in gas chemistry, the choice of trench and film dimensions influences the step coverage. The sticking probability is shown to increase with oxygen flow rate by about 30%, from 0:1 to 10:1 02:HMDSO flow ratio. This flow rate dependence is found to be consistent with work performed on tetraethoxysilane.
Iron Deposition From SC-1 on Silicon Wafer Surfaces
Authors: Dhanda S. , Helms C. R. , Gupta P. , Triplett B. B. , Tran M.
Published: April 2011

This work examines the extent of the deposition of iron on the wafer from (iron) contaminated SC-1 solutions on silicon wafer surfaces, models this effect, and also predicts the chemical state of the iron thus deposited on the wafer surface. The deposition of iron from SC-1 on three different wafer surface terminations was studied. The surfaces were characterized by: (i) the presence of ∼10 Å of native oxide, (ii) by relatively little native oxide and (iii) by a thick thermal oxide. Experiments were performed at room temperature using a 1:1:5 SC-1 (NH4 OH-H2O2-H2O) solution, and also at 80°C with a more dilute composition (0.25:0.5:5). We found that irrespective of the initial surface termination, the amount of iron deposited on the silicon surface from SC-1 exhibited remarkably little deviation over a wide range of spiking levels, leading to the conclusion that in all cases an initial rapid oxidation of the silicon took place, followed by the preferential oxidation of the iron and its inclusion as the oxide into the oxide film. Finally, the model developed predicts that lower temperatures and more concentrated chemistries are more effective in keeping the iron in solution.
Interfacial Defects Induced by Silicidation and Effects of H-Termination at Metal/Silicon Contacts
Authors: Zaima Shigeaki , Yasuda Yukio
Published: April 2011

We have investigated crystallographic structures and electrical properties at the interfaces of transition metals such as Ti, Zr, Hf and V and Si(100), from the viewpoint of an application to ohmic contacts in future ULSI's with low contact resistivity and high reliability. We have achieved very low contact resistivities of 3−5×10−8 Ωcm2 for Zr/ and Hf/n+-Si(100) contacts and 1−2×10-7 Ωcm2 for p+-Si at 400–600°C. It is found that the silicidation reaction in this temperature range brings about the formation of deep levels associated with vacancies in Hf/Si and with metal atoms in V/Si. This difference is considered to be related to that in the silicide formation process between these systems. Furthermore, an anomalous electrical characteristics observed for Hf/p-Si contacts has been found to be markedly improved by using a H-termination treatment of Si surfaces.
IR and MW Absorption Techniques for Bulk and Surface Recombination Control in High-Quaiity Silicon
Authors: Kaniava A. , Menczigar U. , Vanhellemont J. , Poortmans J. , Rotondaro A. L. P. , Gaubas E. , Vaitkus J. , KÖster L. , Graf D.
Published: April 2011

The carrier recombination rate in high-quality FZ and Cz silicon substrates is studied by contactless infrared and microwave absorption techniques. Different surface treatments covering a wide range of surface recombination velocity have been used for the separation of bulk and surface recombination components and evaluating of the efficiency of passivation. Limitations of effective lifetime approach are analyzed specific for low and high injection level. Sensitivity limits of the techniques for iron contamination are discussed
Investigation of Pre-Tungsten Silicide Deposition Wet Chemical Processing
Authors: Philipossian A. , Moinpour M. , Wilkinson R. , Watt V. H. C.
Published: April 2011

Removing the native oxide from the poly-Si surface prior to WSix deposition is essential for achieving high quality silicides as well as sufficient film adhesion, particularly after high temperature anneal or oxidation. Contact angle studies have been used to determine initial and time-dependent surface characteristics of several types of silicon surfaces following immersions in HF-based etchants for varying amounts of time. The morphological characteristics of the surfaces before and after exposure to etchants, as well as the relative etch rates and wetting capabilities of the etchants have been used to explain the following results: With respect to initial contact angle studies, the implanted & annealed polycrystalline silicon surface has the lowest contact angle followed by polycrystalline and monocrystalline surfaces. Longer immersion times yield lower initial contact angles. The 0.1% lightly-buffered HF solution results in the highest contact angle followed by the 1% buffered HF solution with surfactant, and the 1% HF solution. With respect to contact angle changes during ambient air exposure time, the asdeposited polycrystalline silicon surface is most stable followed by monocrystalline, and implanted & annealed polycrystalline silicon surfaces. Longer immersion times improve surface stability while the 0.1% lightly-buffered HF solution results in the most stable surface followed by the 1% buffered HF solution with surfactant, and the 1% HF solution.
Rapid Growth of Diamond-Like-Carbon Films by Copper Vapor Laser ablation
Authors: Mclean W. , Warner B. E. , Havstad M. A. , Balooch M.
Published: April 2011

Visible light from a copper vapor laser (CVL) operating with 510 and 578 nm radiation (intensity ratio approximately 2:1), an average power of 100 W, a pulse duration of 50 ns, and a repetition frequency of 4.4 kHz has been shown to produce high quality diamond-like-carbon (DLC) films at fluences between 2xl08 and 5xl010 W/cm2. Maximum deposition rates of 2000 μm.cm2/h were obtained at 5xl08 W/cm2. DLC films with hardness values of approximately 60 GPa were characterized by a variety of techniques to confirm DLC character, hydrogen content, and surface morphology. the presence of C2 in the vapor plume was confirmed by the presence of the C2 Swan bands in emission spectra obtained during the process. Economic implications of process scale-up to industrially meaningful component sizes are presented.
Role of Ions in Bias Enhanced Nucleation of Diamond
Authors: Lannon J.M. , Gold J.S. , Stinespring Cd.
Published: April 2011

Ion-surface interactions are thought to play a role in bias enhanced nucleation of diamond. To explore this hypothesis and understand the mechanisms, surface studies of hydrogen and hydrocarbon ion interactions with silicon and silicon carbide have been performed. the experiments were carried out at room temperature and used in-situ auger analyses to monitor the surface composition of thin films produced or modified by the ions. Ion energies ranged from 10 to 2000 eV. Hydrogen ions were found to modify silicon carbide thin films by removing silicon and converting the resulting carbon-rich layers to a mixture of sp2- and sp3-C. the interaction of hydrocarbon ions with silicon was shown to produce a thin film containing SiC-, sp2-, and sp3-C species. IN general, the relative amount of each species formed was dependent upon ion energy, fluence, and mass. the results of these studies, interpreted in terms of chemical and energy transfer processes, provide key insights into the mechanisms of bias enhanced nucleation.
Conductivity of the Granular Metal Films Obtained by High Dose Ion Implantation into Pmma
Authors: Bazarov V.V. , Petukhov V.Yu. , Zhikharev V.A. , Khaibullin I.B.
Published: April 2011

Thin granular metal films in polymethylmethacrylate(PMMA) have been synthesized by 40 keV Fe+, ag+ or Pb+ ions implantation with fluencies up to 6*1017 ion/cm2. the resistivity of synthesized films was measured in the temperature range from 300K. to 5K. the temperature dependence of the resistivity of PMMA implanted with ag+, Pb+ and small fluence Fe+ obeys the well known law lnR~(l/T)1/2. the samples implanted by high fluence Fe+ reveal rather a different behaviour. at low temperature (T<100K) the curves R(T) fit the formulae inR~lnT. the two mechanisms of conductivity of a granular film are considered: direct tunneling and thermally activated hopping. Combined with the morphology features of films, obtained by high fluence Fe+ implantation, the above mentioned consideration offers a satisfactory explanation of the observed temperature dependence R(T).
Improving the Electrical Conductivity of Composites Comprised of Short Conducting Fibers in a Nonconducting Matrix: The Addition of a Nonconducting Particulate Filler
Authors: Chen Pu-Woei , Chung D. D. L.
Published: April 2011

The addition of a second discontinuous filler (silica fume) that is essentially nonconducting to a composite with a comparably non-conducting matrix (cement) and a conducting discontinuous filler (carbon fibers) was found to increase the electrical conductivity of the composite when the conducting filler volume fraction was less than 3.2%. The maximum conducting filler volume fraction for the second filler to be effective was only 0.5% when the second filler was sand, which was much coarser than silica fume. The improved conductivity due to the presence of the second filler is due to the improved dispersion of the conducting filler. The silica fume addition did not affect the percolation threshold, but the sand addition increased the threshold.
Mechanical Behavior of Eutectic Sn-Ag and Sn-Zn Solders
Authors: Mavoori Hareesh , Vaynman Semyon , Chin Jason , Moran Brian , Keer Leon M. , Fine Morris E.
Published: April 2011

Eutectic Sn-Ag and Sn-Zn solders are currently being investigated as the basis for replacement of Sn-Pb solders. Some mechanical properties of these solder systems - fatigue, tensile, stress relaxation and creep are presented here along with some damage feature observations for eutectic Sn-Ag solder. Semi-empirical modeling, constitutive modeling and numerical simulation based on damage models have been carried out for lifetime prediction. Preliminary agreement of this numerical simulation with experimental results appears encouraging, but the models need further refinement.
Metal - Containing Ferroelectric Liquid Crystals
Authors: Espinet P. , Etxebarría J. , Marcos M. , Pérez-Jubindo M. A. , Ros M. B. , Serrano J. L.
Published: April 2011

Ferroelectric metallomesogens are a new type of ferroelectric liquid crystal which have unique properties arising from the presence of metal atoms. Here we report an overview of results based on the wide range of structural changes, either in the metallic centre or in the organic part, that these compounds offer.

Ferroelectric salicylaldiminate derivatives, imine ortho-palladated dinuclear complexes and ortho-metallated imine-β-diketone mononuclear compounds give rise to chiral smectic C ordered materials with macroscopic polarizations up to 200 nC.cm-2 while their response times are in the range of ms.

Depending on the metal and the structure of the metallomesogens, additional properties such as paramagnetic behavior as well as non-linear optical reponses are described for these new materials. Thus, imine-β-diketone compounds of Pd(II) and Pt(II) are the first metallomesogens ever reported which show second harmonic generation. deff values in the range of 0.03 to 0.06 pm.V-1 at 10 °C below the transition to the SmC* phase have been measured for these materials under phase matching conditions.
Exciton Confinement in Ultrathin Crystalline Organic Films Grown by Organic Molecular Beam Deposition
Authors: Forrest S. R. , Haskal E. I. , Burrows P. E.
Published: April 2011

We use the low temperature fluorescence spectra of organic multiple quantum well samples consisting of the archetype materials, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA); 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), and 3,4,9,10 perylenetetracarboxylic-bis-benzimidazole (PTCBI), to study the effects of quantum confinement on the lowest energy excited and ground electronic states of these molecular crystals. Both the Franck-Condon and the dominant ground state vibronic mode energies are observed to undergo significant shifts with decreasing PTCDA layer thicknesses (ranging from 500Å to 10Å) in PTCDA/NTCDA MQWs, while no such effects are observed for PTCBI/NTCDA MQWs. These results are interpreted in the context of confinement of spatially extended excitons in ultra thin PTCDA layers, whereas the considerably smaller radius PTCBI excitons are not affected over the range of layer thicknesses investigated. These results unambiguously rule out previous hypotheses suggesting that binding of small radius excitons to interfaces results in the blue shifts previously observed in the absorption spectra of PTCDA-based MQWs.
Low Resistivity Aluminum Nitride: Carbon (AIN:C) Films Grown by Metal Organic Chemical Vapor Deposition
Authors: Wongchotiqul K. , Chen N. , Zhang D. P. , Tang X. , Spencer M. G.
Published: April 2011

Low resistivity single crystal aluminum nitride-carbon (AIN:C) films were grown by metal organic chemical vapor deposition (MOCVD). The growth system used ammonia (NH3), trimethylaluminum (TMA), hydrogen (H2), and propane (C3H8) precursors. Films produced with high partial pressure of propane during growth exhibited high conductivity. Van der Paw measurements indicated that the resistivity of the as grown films changed dramatically from 108 ohm-cm for unintentionally doped samples to less than .2 ohm-cm for partial pressures of propane greater than 0.5×10−3 torr. Reflection electron diffraction (RHEED) measurements performed "in situ" just after film growth indicated that the material is single crystal up to a propane partial pressure of 2.5×10−3 torr. P-n junctions of n-type 6H-SiC and p-type AIN:C were fabricated, blue emission (centered at 490nm) was observed from the heterojunction under forward bias.
Low Temperature Epitaxial Growth of AlN & GaN Thin Films by the Method of Ion Beam Assisted Deposition
Authors: Kim Ig-Hyeon , Jeon Chan-Wook , Kim Seon-Hyo
Published: April 2011

The epitaxial layers of AIN and GaN were grown on Si and Sapphire substrate at a relatively low temperature of around 500 °C using the process of reactive ion beam assisted deposition. The optimum ion beam energy for epitaxial growth of AIN and GaN films was found to be about 50 eV. Characterization of the epitaxial layers was carried out by GID (Grazing-Incidence x-ray Diffraction) and high resolution TEM observation. The orientational relations between epitaxial layer and substrate were determined through these analysis. Very thin amorphous layers were observed at the interfaces of bom AIN and GaN films grown on Si(111) substrate, whereas the films grown on Sapphire substrate has no amorphous layer. The amorphous layer may act as a buffer layer enabling the growth of the epitaxial layers of AIN and GaN by relaxing the misfit strain in the early growing stage.
High-Precision Characterization of III-Nitride Semiconductor Alloys with Secondary Ion Mass Spectrometry (SIMS)
Authors: Erickson J W. , Gao Y. , Wilson R. G.
Published: April 2011

Samples of representative AlxGayIn1−x-yN compositions have been studied with secondary ion mass spectrometry (SIMS). First, ionized species of common interest (H, B, C, O, Mg, Si, and Cd) were implanted into the Ill-nitride samples to provide calibrated standards. Depth profiles and conversion factors for quantification of dopants were then obtained using O2+ or Cs+bombardment and positive or negative SIMS to measure B+ and Mg+; H−, B−, C−, O−, and Si−; and CdCs+. In addition calibration curves for quantification of stoichiometry were prepared using MCs+ ions (NCs+, AlCs−, GaCs+, InCs+) for which the ion yields are relatively independent of the matrix composition; and using atomic, dimer, and trimer ions (Al, Ga, In, Al2, Ga2, In2, Al3, Ga3) which are very sensitive to matrix composition. The empirical calibration curves show small non-linearities. Dopant concentrations can be quantified with great sensitivity (detection limits usually below 1 ppm), accuracy (usually better than 10%), and precision (better than 25%). Matrix stoichiometry can be quantified with an accuracy of about 1–3%.
A Microscopic Evaluation of the Surface Structure of OMVPE Deposited α-GaN Epilayers
Authors: Rohrer G. S. , Payne J. , Qian W. , Skowronski M. , Doverspike K. , Rowland L. B. , Gaskill D. K.
Published: April 2011

The surface structure of organometallic vapor phase epitaxy (OMVPE) grown α-GaN films was investigated using optical and scanning force microscopy (SFM). Optical microscopy shows that the surface is decorated with several different types of faceted features that have lateral dimensions of 10 to 75 μm and occur with a density of approximately 104/cm2. SFM images show that on the flat regions of the surface, single diatomic layer steps, 2.6 Å high, are straight, evenly spaced (at 500 to 1500 Å intervals), and oriented along á101ñ directions. The SFM images also show that the regular step patterns are often interrupted by faceted growth hillocks, 0.8 to 5 μm in diameter and 120 to 400 Å high, that occur with a density of 106/cm2. An open-core screw dislocation with a Burgers vector of 5.2 Å occurs at the center of each hillock and is a source for spiral steps. Other dislocations are also observed to intersect the flat regions of the surface and create a step, but these have smaller Burgers vectors, do not form spirals, and do not have open cores. Based on these observations, we conclude that thick OMVPE GaN films grow by a combination of the layer-by-layer and spiral growth mechanisms.
Defect Studies of GaN under Large Hydrostatic Pressure
Authors: Wetzel C. , Fischer S. , Walukiewicz W. , Ager III J. , Haller E.E. , Grzegory I. , Porowski S. , Suski T.
Published: April 2011

GaN plays a key role in the exploration of the properties of group-Ill nitrides. As grown GaN often shows a high electron concentration, e.g. 1019 cm−3, of as yet unidentified origin. Applying large hydrostatic pressure we studied the behavior of these donors and a frequently observed strong luminescence band at 3.42 eV. We find a drop of the electron concentration to 3×1017 cm−3 at 27 GPa and derive a binding energy of 126 meV for the neutral singlet donor level at this pressure. Such a pressure behavior of a donor is consistent with the model of strongly localized defects. Within the framework of a bandstructure calculation we predict the neutral level of this donor at 0.40 ± 0.10 eV above the conduction band edge at ambient pressure.
Shallow and Deep Level Defects in GaN
Authors: Götz W. , Johnson N.M. , Bour D.P. , Chen C. , Liu H. , Kuo C. , Imler W.
Published: April 2011

Shallow and deep electronic defects in MOCVD-grown GaN were characterized by variable temperature Hall effect measurements, deep level transient spectroscopy (DLTS) and photoemission capacitance transient spectroscopy (O-DLTS). Unintentionally and Si-doped, n-type and Mg-doped, p-type GaN films were studied. Si introduces a shallow donor level into the band gap of GaN at ∼Ec - 0.02 eV and was found to be the dominant donor impurity in our unintentionally doped material. Mg is the shallowest acceptor in GaN identified to date with an electronic level at ∼Ev + 0.2 eV. With DLTS deep levels were detected in n-type and p-type GaN and with O-DLTS we demonstrate several deep levels with optical threshold energies for electron photoemission in the range between 0.87 and 1.59 eV in n-type GaN.