bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Contact Overlap Distance on a-Si Tft Performance
Authors: Uchikoga Shuichi , Akiyama Masahiko , Koizumi Takashi , Ikeda Mitsushi , Suzuki Kouji
Published: March 2011

The gate/source overlap distance (ΔLs) is an important factor in fabricating self-aligned TFT with passivating layer. Six types of TFT were fabricated using thin intrinsic a-Si layers such as 20 nm,50 nm and 100 nm and a n+:a-Si or a n+:μc-Si were used as the contact layer. The least required gate/source overlap distance, ΔLsC is the critical overlap where the TFT performance is not limited by the contact. This ΔLsc was determined experimentally. ΔLsC was found to be significantly affected by the intrinsic a-Si layer thickness and the ΔLsc can be small by depositing a thin intrinsic layer. The intrinsic layer thickness dependence of ΔLsC in the linear region can be explained from a existing model. However, the behavior in the saturation region suggests the need of another model, which will be discussed here. The variation of n'contact layer shown to have a small effect on ΔLsc. In order to determine appropriate ΔLs for self-alignment TFT, the magnitude of field effect mobility, threshold voltage and drain current as well as ΔLscmust be considered.
The doping of a-Si:H with liquid boron and phosphorus sources
Authors: Albert M. , Schade K. , Beyer W.
Published: March 2011

The conductivity control of amorphous hydrogenated silicon (a-Si:H) by incorporation of electron donors or acceptors is prerequisite for the application of these layers in devices. The doping sources B2H6 and PH3 which are usually highly toxic are substituted by not dangerous boron and phosphorus liquid sources based on hydro-carbons. The avoidance of gas cylinders and expensive safety measure techniques is another advantage of these liquids.

In this paper we have studied the influence of boron, phosphorus and carbon on the electrical, photoelectrical and optical properties. The layers were produced in a capacitively coupled reactor in a silan-doping gas mixture. The maximum of the dark conductivities (300K) of the p- and n-type a-SiC.,:H layers was 10-5 and 103 (Ωcm)-1, respectively, the activation energys decreases to 0.4 and 0.2 eV respectively. With a high quantity within the range of doping gas in the mixture, the carbon determines the layer properties. At a gas mixture ratio of 1:1 ( silan: doping gas) the optical gap expands to 2.7 eV and the dark conductivity decreases below 10∼13 (Ωcm)-1.
Factors Affecting Image Quality for Megavoltage and Diagnostic X-Ray a-Si:H Imaging Arrays.
Authors: Antonuk L.E. , Yorkston J. , Huang W. , Boudry J. , Morton E.J. , Longo M.J. , Street R.A.
Published: March 2011

Two factors which could affect the image quality of the a-Si:H arrays under development by our collaboration are the temporal drift of the leakage current of the sensors and the capture and release of charge in deep trapping states in the sensors. Data for both of these factors are reported, the implications for imaging are discussed, and strategies for reducing or eliminating their effects are suggested.
Application of Analogue Amorphous Silicon Memory Devices to Resistive Synapses for Neural Networks
Authors: Reeder A A , Thomas I P , Smith C , Wittgreffe J , Godfrey D J , Hajto J , Owen A E , Snell A J , Murray A F , Rose M J , Osborne I S , LeComber P G
Published: March 2011

The amorphous silicon memory device shows promise as an analogue weight element in neural networks. The device resistance can be programmed to within 5% of any specific value between lkΩ and lMΩ using 10ns to 1μ voltage pulses in the range 1–5V. In this paper we describe the physical structure of the element and its electrical characteristics. Finally, a simple example is discussed of a small neural network implementing the EXOR function using amorphous silicon memory elements as a resistive array of weights and external op-amps as the current summing nodes.
Large Area 2-Dimensional a-Si:H Imaging Arrays
Authors: Street R. A. , Fujieda I. , Weisfield R. , Nelson S. , Nylen P.
Published: March 2011

Six inch diagonal, two-dimensional amorphous silicon imaging arrays with 256×240 pixels of 450 micron pitch have been fabricated. Examples of images made under visible light and X-rays illustrate applications to electronic document input and medical imaging. The limits to the array performance are explored through studies of image lag due to deep trapping at dangling bond defects in the a-Si:H sensor, and through measurements of electronic noise.
Pulsed Laser-Induced Crystallization and Amorphization of SiGe Films.
Authors: Sameshima T. , Usui S.
Published: March 2011

Pulsed laser-induced melting followed by crystallization and amorphization were studied on silicon-germanium alloy (SiGe) films. Although amorphization was achieved on SiGe films, it was not observed in pure Ge films. Crystalline nucleation density in homogeneous solidification increased as Ge concentration increased. It was 1×1024m-3for Si0.22Ge0.78 films, while it was 4×1022m-3 for pUre si films. Electrical conductivity of laser polycrystallized films increased as Ge concentration increased. It had a maximum of 1 S/cm when Ge concentration was 0.78. This high electrical conductivity would be brought about by the increase of carrier mobility as well as the reduction of the band gap.
Investigation of Optimal Photosensor in A-Si:H Liquid Crystal Light Valves
Authors: Du Piyi , Han Gaorong , Qiao Jianmin , Han Weiqiang , Zhao Danmei , Ding Zishang
Published: March 2011

The a-Si:H thin film is used for a photosensor in liquid crystal light valve(LCLV). A lumped element model for the layered a-Si:H LCLV is developed. It has been shown that the dark and photo-resistances of the a-Si:H photosensor should be adjusted respectively to within the region between one order of magnitude higher and one order of magnitude lower than that of the liquid crystal(LC) layer to ensure a linear variation of the voltage across the LC with the intensity of the incident write-light beam. For obtaining an optimal operation condition of the LCLV, we can determine the concrete values of the dark resistance of the photosensor from the threshold voltage of the LCLV for the linear change of the LCLVs grey level and the applied voltage of the LCLV, and the photoresistance of the photosensor from the saturation voltage of the LC. As a result, the application of an a-Si:H film by optimization of the deposition condition indicates that the contrast of LCLV can be improved distinctively.
Diagnostics of VHF Plasma Deposition
Authors: Kuske J. , Stephan U. , Schade K. , Fuhs W.
Published: March 2011

The use of Very High Frequency (VHF) glow discharge for the deposition of amorphous silicon films is one approach to influencing the deposition conditions.

For the experiments a capacitatively-coupled parallel plate reactor with two aluminium electrodes of 125 mm in diameter is used. The VHF is generated by means of an all-solid state amplifier which has a frequency response ranging from 250 kHz to 150 MHz. Experiments with an nitrogen discharge within the range from 5 to 150 MHz are an principle in agreement with the results in the literature. The results show, that the frequency dependence of the discharge strongly depends on the design and the external electrical connection of the VHF-reactor. In the examined range of frequency resonances appear, which are probably responsible for the maximum of the deposition rate. These resonances are not essentially resultant from changes in the physics of the discharge but a result of the reactor construction and the external electrical connection. Possibilities which influence this frequencies of resonance will be discussed.

Results for an electrical network model will be discussed in the comparison with different reactors and the optimization of the behaviour of the deposition process.
Dependence of the a-Si:H Defect Density of States on the Magnetic Field Profile of an Electron Cyclotron Resonance Microwave Plasma
Authors: Pool F.S. , Essick J.M. , Shing Y.H. , Mather R.T.
Published: March 2011

The magnetic field profile of an electron cyclotron resonance (ECR) microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. Films of a-Si:H were deposited at pressures of 0.7 mTorr and 5 mTorr with a H2/SiH4 ratio of approximately three. The mobility gap density of states ND, deposition rate and light to dark conductivity were determined for the a-Si:H films. This data was correlated to the magnetic field profile of the plasma, which was characterized by Langmuir probe measurements of the ion current density. By variation of the magnetic field profile ND could be altered by more than an order of magnitude, from 1×1016 to 1×1017 at 0.7 mTorr and 1×1016 to 5×1017 at 5 mTorr. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration.
Defect States and Structural Disorder in a-Si.
Authors: Davidson B. N. , Lucovsky G. , Bernholc J.
Published: March 2011

We have examined the distribution of the neutral dangling bond defect states, T30, as a function of the local disorder. T30 defects in a-Si play an important role in many of the current models of the metastable photoconductivity. To understand the relationship between the T30 defect and its bonding environment, the Local Density of States (LDOS) for under-coordinated Si atoms in disordered environments are calculated using the cluster-Bethe lattice method, CBLM. Our Hamiltonian employs the tight-binding parameters of an sp3 orbital basis containing both 1st and 2nd nearest-neighbor interaction terms fit to c-Si band structure. Averaged LDOS of atoms with various bond angle distortions are calculated in order to demonstrate the relationship between the standard deviation in bond angle and the width of the defect states. The CBLM is also used to determine the extent of the valence band tails as a function of the standard deviation in bond angle. In addition, the LDOS of clusters with 2 dangling bonds are examined to determine the degree that their energy levels split due to their interaction with each other.
Modification of a-Si(:H) by Thermally Generated Atomic Hydrogen: A Real Time Spectroscopic Ellipsometry Study of Si Bond Breaking
Authors: An Ilsin , Li Youming , Wronski C.R. , Collins R.W.
Published: March 2011

We have applied real time spectroscopie ellipsometry (2.5≤hv≤4.5 eV) to investigate in situ hydrogenation of thin film a-Si:H prepared by plasma-enhanced CVD. When a-Si:H is exposed to atomic H generated by a tungsten filament heated in H2, as many as ∼5×1021 Si-Si bonds/cm3 can be converted to Si-H bonds in the top ∼200 Å of the film. We have determined the spectroscopie characteristics of Si-H bonds from optical to near-uv photon energies through an analysis of the changes in the dielectric function of the near-surface of the film upon hydrogenation. The conversion of Si-Si bonds to Si-H bonds is identified as reaction-limited to a depth of ∼500 Å. We find that a surface oxide a few monolayers in thickness acts as an effective diffusion barrier to H-incorporation.
In Situ Monitoring of Interfaces and Growth of Amorphous Silicon by Spectroellipsometry
Authors: Drevillon B.
Published: March 2011

Recent applications of spectroscopie phase modulated ellipsometry, from 0.25 to 11 μm, to study the growth of plasma deposited thin film semiconductors like amorphous (a-Si:H) silicon are reviewed. The high sensitivity of this technique is emphasized. In the infrared (IR), the hydrogen incorporation during a-Si:H growth can be precisely investigated. Photoelectronic quality a-Si:H films grow beneath a hydrogen rich overlayer (a few monolayers thick) containing SiH2. the hydrogen being bonded as SiH in the bulk material. In the ultraviolet (UV) range, the ability of kinetic ellipsometry, with fast time resolution, to study interfaces formation is illustrated. Examples of sharp interfaces are presented. In the case of amorphous silicon-silicon nitride structures, it is shown that an inversion of the deposition sequence of the various layers can lead to a graded transition. A detailed analysis of a growth process involving a chemical reaction with the substrate is illustrated in the case the a-Si:H / Pd interface.
AB Initio Calculations for Defects in Silicon-Based Amorphous Semiconductors
Authors: Ishii Nobuhiko , Shimizu Tatsuo
Published: March 2011

We have calclulated the ESR hyperfine parameters of threefold-coordinated Si atoms and twofold-coordinated P and N atoms in Si-based amorphous semiconductors using the density functional theory with a local-spin-density approximation. These calculated results have been compared with the observed ESR results.
Correlations of Changes in ESR and PL with Light Soaking in a-Si:H
Authors: Yoshida Mihoko , Taylor P.C.
Published: March 2011

Light-induced changes in electron spin resonance (ESR) signal intensity and photoluminescence (PL) intensity in device quality a-Si:H are compared. Different dependences on the light soaking temperature for the ESR spin density and the PL peak intensity at ∼ 1.3 eV suggest that a non-radiative process, that does not directly involve neutral dangling bonds, influences the photoluminescence at the peak. After light soaking no clear increase of the peak in the low energy luminescence region (∼ 0.8 eV) was observed even at higher temperatures (> 200 K), where the low energy luminescence band is relatively more important.
The Mechanism for Defect Generation Studied by Photodegradation of A-Si:H Solar Cells Under Electrical Bias
Authors: Yang Liyou , Chen L. , Hou J.Y. , Li Y.M.
Published: March 2011

The light induced degradation of a-Si:H p-i-n solar cells under electrical bias has been systematically studied. By comparing the results with the light intensity dependence of cell degradation under open circuit condition, we show that the only recombination mechanism, which can be consistent with the experimental data in both cases, is based on the bimolecular recombination between a free hole and a trapped electron at the “weak” bond site. Other possibilities for defect creation are also pointed out.
Light-Induced Effects in a-Si:H Films Fabricated by Intense Light-Flash Assisted Plasma CVD, and Its Application to the Stabilisation of a-Si:H Solar Cells
Authors: Nevin W.A. , Yamagishi H. , Fujihara T. , Takenaka A. , Yamaguchi M. , Tawada Y.
Published: March 2011

We describe a new technique for the deposition of a-Si:H, in which the growing film surface is periodically irradiated with high-intensity xenon light pulses. The films show high stability of the photoconductivity under illumination, but also exhibit a high dark conductivity, so that the photosensitivity is reduced. Infrared and Raman scattering measurements indicate little difference in the Si-H and Si-Si bonding structures compared to reference films; however, there is a large increase in the sub-bandgap absorption in addition to a shift of the Fermi level, implying some subtle modification of the film growth process caused by the irradiation. Results on the preparation and stability testing of solar cells fabricated using this technique are also described.
Kinetics of Dopant Metastability in a-Si:H
Authors: Nebel C. E. , Street R. A. , Johnson N. M. , Jackson W. B.
Published: March 2011

Small temperature-induced perturbations from thermodynamic equilibrium of doped hydrogenated amorphous silicon (a-Si:H) are explored by dark conductivity measurements. The equilibration kinetics reveal significant differences between phosphorus and boron doping. Raising the temperature leads to an increase of electron/hole densities which are related to the activation of additional dopants, while a decrease of temperature causes the opposite effect of dopant passivation. The creation kinetics of P doped a-Si:H is stretched exponential with a temperature independent β value of 0.85 whereas dopant passivation in the same temperature range is also stretched exponential decay, but with values for β < 0.8. In contrast, the kinetics of boron activation and passivation are stretched exponential with equal β values. The time constant τ to achieve thermodynamic equilibrium for both activation and passivation is thermally activated with energies ≃ 1.1 eV for P and B doped a-Si:H. τ depends weakly on the degree of perturbation. A discussion and interpretation of the data based on hydrogen migration in a-Si:H is given.
Effect of Light-Soaking on the Density of States and Carrier Dynamics of a-Si1-xGex:H Alloys
Authors: Unold Thomas , David Cohen J. , Fortmann Charles M.
Published: March 2011

We have used transient and steady-state junction capacitance methods to gain information about the density of states in the mobility gap of silicon-germanium alloys a-Si1-xGex:H (0.25<×<1.0). With those measurements we are also able to differentiate between minority and majority carrier processes in the alloys. We find that the (μτ)p is considerably reduced from its value in a-Si:H, even for films with small germanium concentrations (x=0.25). The density of states deduced from the optical spectra shows two distinct features above and below midgap for all concentrations, which both increase with light-soaking. Light-soaking also sharply reduces the (μτ)p.
Comparison of A-Si:H Films Prepared by RP- and Conventional P-CVD
Authors: Kim Sung Chul , Park Kyu Chang , Kim Sung Ki , Kim Tae Gon , Pyun Jae Sung , Jun Jung Mok , Jang Jin
Published: March 2011

We have studied the effect of RF power on the properties of Si thin films prepared by a conventional plasma and remote plasma(RP)- CVD. The structure of the Si film changes from amorphous to crystalline with increasing RF power in RP-CVD. However, the structure of Si film deposited by P-CVD remains amorphous with increasing RF power. The relaxation of Si atoms by means of chemical annealing of He metastable atoms gives rise to the formation of macrocrystalline structure at the high RF powers.
Structure and Carrier-Transport in a-Si:H, a-Si(Ge): H Films Prepared by Chemical Annealing
Authors: Shirai Hajime , Nakamura Kenjiro , Azuma Masanobu , Hanna Jun-ichi , Shimizu Isamu
Published: March 2011

The stability and opto-electric properties of a-Si:H films fabricated by “chemical annealing (CA)” with excited states of He (He*) were systematically investigated. The films made by the CA mode showed a high photoconductivity due to a low level of defect density, 2×1015cm-3, and improvement in the stability against light soaking. A marked improvement was also found in the hole-transport in films fabricated by the CA. The structural relaxation on the growing surface was also enhanced by addition of a small amount of Ge.
Effects of Gas Dilution on the Growth and Properties of Glow Discharge a-Ge:H
Authors: Chen J. H. , Wickboldt P. , Pang D. , Wetsel A. E. , Paul W.
Published: March 2011

We compare films of a-Ge:H deposited by plasma enhanced chemical vapor deposition (PECVD) using GeFLi diluted with H2, He and Ar. The nominal deposition conditions used were those which have produced high quality a-Ge:H with H2 dilution. Using H2 and He as diluents, three studies were done in which the parameters of substrate temperature, diluent gas flow and electrode gap spacing were independently varied. The photoelectronic properties of the films made with He dilution were quite good, although never better than those made with H2 dilution. The overall results indicated that for our nominal conditions hydrogen plays an important and crucial role in producing high quality films, and we believe that this role is mainly to reduce the probability of germane radical incorporation. In contrast to He and H2 dilution, dilution with Ar produced films with much poorer microstructure and a photoresponse two orders of magnitude lower. We attribute this to polymerization of the germane radicals which led to observed dust particles and a reduction in ion bombardment of the growing film.
Recombination Lifetimes in a-Si:H/a-SiC:H Multilayers
Authors: Muschik T. , Fischer T. , Schwarz R.
Published: March 2011

The recombination processes in a-Si:H and a-Si:H/a-SiCo.3s:H multilayers at T=10 K are studied by transient photoluminescence on a time scale from 2 ns to 100 ms. Our investigations yield a lifetime distribution with two peaks at ∼1 ms and ∼1 /μS for bulk a-Si:H. We present measurements on samples with varying defect density ND. It is shown that there is no significant shift of the two lifetimes as a function of ND. However, the relative contribution of the μs-peak is enhanced with increasing ND. In a-Si:H/a-SiC:H multilayers with a varying number of interfaces and well layer thicknesses dsi there is also no discernible change of the lifetimes as a function of the overall defect density. An additional peak at ∼20 ns is observed for samples with dsi smaller than ∼30 Å. It may be attributed to recombination in the interface layers.
Influence of Carbon on Structural, Optical and Electrical Properties of Microcrystalline Silicon Carbide.
Authors: Demichelis F. , Pirri C.F. , Tresso E. , DellaMea G. , Quaranta A. , Rigato V. , Ferraris M. , Rava P.
Published: March 2011

Microcrystalline films of SiC.H have been deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) of SiH4+CH4+H2 mixtures with high power density and high H2 dilution, at variable CH4/SiH4 ratios. Their elemental composition, structural, optical and electrical properties have been investigated in order to evidence the influence of hydrogen and carbon on microcrystallinity.
Optoelectronic Properties of a-SiC:H Studied by Time-Resolved Microwave Photoconductivity and Photoinduced Absorption Measurements
Authors: Swiatkowski C. , Herm D. , Hirsch W. , Kunst M.
Published: March 2011

The optoelectronic properties of a-SiC:H alloys with different carbon content are investigated with time resolved photoconductivity and photoinduced absorption measurements. It is shown that the electron drift mobility decreases with increasing carbon content. Also a weak increase of deep electron trapping with increasing carbon content is suggested by the experimental data. The recombination does not seem to be strongly changed by the presence of carbon at least at low carbon content.
Comparison of a-Si1-xCx:H Layers Based on Methane, Di-, Tri- and Tetrasilylmethane as Feedstocks
Authors: Fölsch J. , Rubel H. , Schade H.
Published: March 2011

Using standard rf glow discharge deposition, we compare the properties of a-Si1-xCx:H films prepared with different carbon sources, namely methane and di-, tri- and tetrasilylme-thane (DSM, TSM and TetraSM). The optical bandgap EG was varied between 1.8 eV and 2.4 eV. All oua-Si1-xCx:H films exhibit low Urbach energies (EQ < 60 meV for EG< 2.0 eV) and low defect absorption, both determined by PDS. Using the silylmetha-nes as feedstocks, we do not find significant differences relative to our methane-based material. Independently of the carbon source material, the energy gap dependences of the film properties (photoconductivity, activation energy of the dark conductivity, Urbach energy and subbandgap defect absorption) show a distinct change around EG = 2.1 eV, which is interpreted as a consequence of structural changes with increasing carbon content.
The Photocarrier Grating and Its Applications in the Study of A-Si:H Materials and Devices
Authors: Balberg I.
Published: March 2011

To date the photocarrier grating (PCG) technique is widespread among a- Si:H researchers. This technique is presently the only available technique for the determination of the minority carrier diffusion length in materials where this length is in the submicron range. The basic idea or the PCG technique will be presented, and results which follow its fruitful use in the study of a-Si:H materials and devices will be reviewed. Finally some future studies of these materials by the PCG method will be suggested.
The Extended State Mobility in Amorphous Silicon Alloys
Authors: Fauchet P.M. , Vanderhaghen R. , Mourchid A. , Hulin D.
Published: March 2011

The total scattering time of free carriers injected optically in the extended states of amorphous semiconductors has been measured using the techniques of femtosecond time-resolved spectroscopy. We find that this scattering time is less than 1 femtosecond, independent of alloy composition (a-Si:H, a-Si,Ge:H, a-Si,C:H) and temperature (from 77 K to 400 K). The extended state mobility deduced from the measurement of the scattering time and of the effective mass is approximately 6 cm2/Vs. A model is proposed to explain these results
A Correlation between Si Surface Micro-Roughness and Atomic Concentration on Surface: Application to Micro-Roughness Measurement of Si
Authors: Oki I. , Biwa T. , Kudo J. , Shibayama H.
Published: March 2011

We have developed a new method of evaluating Si surface micro-roughness, by forming thin oxide in HCI/H2O2 solution and then measuring the concentration of chlorine atoms or the total charge in this oxide. It is shown that this oxide does not affect the surface micro-roughness, and the surface concentration of chlorine atoms incorporated in this oxide and the total oxide charge are proportional to the surface micro-roughness, as obtained by AFM. From these correlations, it is possible to evaluate the surface microroughness for large areas compared with the areas of AFM measurement.
TXRF Characterization of Trace Metal Contamination in Thin Gate Oxides
Authors: Hockett R. S. , Hymes Diane
Published: March 2011

Metal contamination on the surface of silicon substrates before gate oxidation is known to affect gate oxide reliability. For the first time this study presents a non-destructive, analytical measurement of transition metals in an 8nm gate oxide grown by a 920 °C-10min-dry oxidation of an intentionally contaminated silicon surface. The TECHNOS TREX 610 TXRF anglescan of the gate oxide provides qualitative information on the location of the metals. The data indicate the Fe is on or in the oxide, the Cu is below the oxide, the Zn is on the oxide, and the Ni may be both in the oxide and below the oxide layer. In addition, quantitative estimates from the TXRF data indicate that all the original Fe and Cu are present, while only portions of Zn and Ni are detected after the oxidation.
In Situ Contamination Control Investigation of Silicon Nitride Low Pressure Chemical Vapor Deposition Process in Vertical Thermal Reactors
Authors: Moinpour Mansour , Bohannan K. , Shenasa M. , Sharif A. , Guzzo G. , Brestovansky D.F. , Markle R.J. , Wilkes R.
Published: March 2011

A contamination control study of a Silicon Valley Group Thermco Systems Vertical Thermal Reactor(VTR) is presented. Trace elements of contaminants such as water vapor and oxygen have been shown to significantly affect the integrity of the silicon nitride film deposited by the low pressure chemical vapor deposition (LPCVD) process. This study documented the effects of process parameters on gaseous contamination levels, i.e., O2 and H2O vapor. Starting with a baseline process, the effects of an excursion of pre-deposition temperature ramp-up and stabilization condition, wafer load/unload and various post deposition conditions were explored. An axial profile of moisture and oxygen levels along the wafer load was obtained using Linde's Low Pressure Reactor Analysis(LPRAS) methodology. In addition, other process parameters such as gas flow rates during load and unload of wafers, pre-deposition N2 purge and process tube exposure time to ambient environment were- investigated. The wafers were analyzed for contaminants on the wafer surface or in the deposited silicon nitride film using FTIR and Auger spectroscopy techniques. They showed low levels of Si-O and no measurable Si-H or N-H bonds.
Surface Characterization of Chemical-Mechanical Polished GaAs by Inclined Bragg Plane Triple Crystal X-Ray Diffraction
Authors: Wang Victor S. , Matyi Richard J.
Published: March 2011

The incorporation of triple crystal x-ray diffraction (TCD) under conditions of a nearly grazing incident x-ray beam provides a unique capability to characterize surface and subsurface structural damage. The effects of bromine-methanol chemical-mechanical (CM) polishing on the surface quality of GaAs were investigated by inclined Bragg plane triple crystal x-ray diffraction. GaAs samples polished under varying conditions of Br2 concentration, total polish time, polish wheel rotation speed, and force exerted on the samples were analyzed using TCD profiles from inclined (220) planes, with the samples oriented at both the exact Bragg condition, θB, and at deviations from the exact Bragg condition. As the deviation from the 220 reciprocal lattice point was increased, multiple peaks corresponding to both the dynamic and the kinematic components were observed. The peak positions and the relative intensities of the various peaks were used to characterize the effects of the CM polishing variables on the GaAs surfaces.
Surface Characterisation of Si After HF Treatments and its Influence on the Dielectric Breakdown of Thermal Oxides
Authors: Verhaverbeke S. , Alay J. , Mertens P. , Meuris M. , Heyns M. , Vandervorst W. , Murrell M. , Sofield C.
Published: March 2011

The characteristics of the HF-treated Si-surface are investigated as a function of dipping time in dilute HF solutions. It is found that the contact angle is a very sensitive measure for the degree of oxidation of the Si-surface. The importance of obtaining a perfectly passivated surface in order to reduce the particle deposition on the surface is shown. HF-last cleans are found to be beneficial in terms of metallic contamination and gate oxide integrity. The importance of the loading ambient in furnaces is investigated after HF-treatments and RCA-cleans.
In Situ Low Temperature Cleaning and Passivation of Silicon by Remote Hydrogen Plasma for Silicon-Based Epitaxy
Authors: Banerjee S. , Tasch A. , Hsu T. , Qian R. , Kinosky D. , Irby J. , Mahajan A. , Thomas S.
Published: March 2011

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD), which involves nonthermal, remote plasma excitation of precursors, has been demonstrated to be a novel and attractive technique for low temperature (150-450C) Si and Sil-xGex epitaxy for applications in Si ULSI and novel Si heterostructure devices which require compact doping profiles and/or heterointerfaces. An in situ low temperature remote hydrogen plasma clean in the Ultra-High Vacuum (UHV) deposition chamber in order to achieve a chemically passive, hydrogenated Si surface with minimal O, C and N contamination, is a critical component of the process. The ex situ wet chemical cleaning consists of ultrasonic degreasing and a modified RCA clean, followed by a final dilute HF dip. The in situ clean is achieved by remote plasma excited H, where H introduced through the plasma column is r-f excited such that the plasma glow does not engulf the wafer. In situ AES analysis shows that the remote H plasma clean results in very substantial reduction of the C, O and N contamination on the Si surface. We believe that the H plasma produces atomic H which, in turn, produces a reducing environment and has a slight etching effect on Si and SiO2 by converting them to volatile byproducts. TEM analysis of the wafers subjected to this clean indicate that defect-free surfaces with dislocation loop densities below TEM detection limits of 105 /cm2 are achievable. Corroborating evidence of achieving an atomically clean, smooth Si surface by remote H plasma clean as obtained from in situ RHEED analysis will also be presented. After in situ H cleaning at low pressures (45 mTorr), typically for 30 min. at a substrate temperature of 310 C, we observe both stronger integral order streaks compared to the as-loaded sample and the appearance of less intense half-order lines indicative of a (2 × 1) reconstruction pattern, indicating a monohydride termination. A (3 × 1) reconstruction pattern is observed upon H plasma clean at lower temperatures (250 C), which can be attributed to an alternating monohydride and dihydride termination. Results of air exposure of hydrogenated Si surfaces by AES analysis indicate that the (3 × l) termination is chemically more inert towards readsorption of C and 0. Successful Si homoepitaxy and Si/Sil-xGex heteroepitaxy under a variety of surface cleaning conditions prove that by a combination of these cleaning techniques, and by exploiting the inertness of the H-passivated Si surface, very low defect density films with 0 and C levels as low as 1X1018 cm−3 and 5×1017 cm−3, respectively, can be achieved.
Vapor HF Etching for Low Temperature Silicon Epitaxy
Authors: D'Emic Christopher P. , Blum Joseph M. , Cohen Susan L. , Baseman Robert J. , Gilbert Monica , Cardone Frank , Stanis Carol , Rothman Laura , Hill Michael , Krusell Wilbur
Published: March 2011

We have evaluated the use of HIF vapor cleaning using an Advantage Edge 2000 commercial etcher as a preclean for low temperature UHV/CVD silicon epitaxy (LTE). Surface analysis by contact angle, XPS and Optically Stimulated Electron Emission (OSEE) measurements indicate that vapor HF treated surfaces have higher levels of impurities and are less stable than surfaces dipped in 10:1 diluted HF. Interfacial SIMS measurements and defect analysis using plan-view TEM after epitaxial growth indicate that the vapor treated samples also had higher levels of interfacial oxygen and surface defects. The results indicate that vapor HF precleaning is less effective for LTE than an aqueous HF dip since it provides poorer quality hydrogen passivation of the silicon surface.
Characterization of SiGe Epitaxial Films Using Ellipsometry and X-Ray Fluorescence
Authors: Munukutla L.V. , Evans K. , Liaw M.H.
Published: March 2011

Ellipsometry in combination with X-ray fluorescence spectroscopy is demonstrated as a suitable technique to characterize SiGe thin films (180–800 Å) rapidly and nondestructively. Film thickness values extracted from ellipsometry are in agreement with the measurements obtained using other techniques such as TEM, SIMS, and RBS. The measured Ge concentration obtained by direct excitation of X-rays in several SiGe films ranging from 6 to 20 atomic percent, shows good correlation with the values obtained using RBS and SIMS.
Pre-Oxidation Anneal Kinetics: Interface Degradation of Thin SIO2 Films on Silicon
Authors: Poler J.C. , Irene E.A.
Published: March 2011

The high temperature anneal of hydrogen terminated silicon has been shown to etch and roughen its surface. We attempt to describe the degree of this roughness and the time scale on which it occurs using several electrical measurements: excess direct tunneling currents, dielectric breakdown and the oscillations in the Fowler-Nordheim tunneling currents. From these results we draw conclusions on the time and water content dependence of pre-oxidation annealing on the microroughness of the Si/SiO2 interface.
Development of High Temperature and Pressure Eh And Ph Sensing Instruments
Authors: Danielson M.J. , Koski O.H. , Myers J.
Published: March 2011

The design, testing, and calibration of metallic Eh and zirconia pH sensors for use at elevated temperatures and pressures are discussed.
Actinide and Technetium Solubility Limitations in Groundwaters of Crystalline Rocks
Authors: Allard B.
Published: March 2011

The solubility and speciation of U, Np, Pu, Am and Tc in deep groundwaters from crystalline rocks have been calculated. The solution chemistry of these elements is largely determined by the redox conditions (Eh = 0.24 − 0.06pH ± 0.06 V, based on measurements of Fe(II)), pH (usually 7 − 9) and the presence of carbonate (log [CO32-] from (pH − 14) to (0.76pH − 10.83), based on measurements of HCO3-). The oxidation states U(IV)(+VI), Np(IV), Pu(III)(+IV), Am(III) and Tc(IV) dominate, with the tetravalent oxides (U, Np, Pu, Tc) and Am2(CO3)3(s) as solubility limiting phases. Maximum concentrations in the range 10-9− 10-10M or below would be expected for U, Np and Tc under reducing conditions, somewhat higher for Pu and still higher (10-6− 10-7M) for Am.
Design Considerations To Minimize The Impact Of A Repository On A Host Rock
Authors: Scully Leo W.
Published: March 2011

A conceptual design is being developed in support of the Department of Energy's study of a potential site for a nuclear waste repository at Yucca Mountain. This design can be used to support the recommendation of that site for characterization if so designated by the Department of Energy. In the event that the Yucca Mountain site is chosen for development as the first repository, the conceptual design and subsequent preliminary engineering designs could be used to develop design specifications for repository construction. The design addresses the unique surface and subsurface characteristics of the volcanic tuffs at Yucca Mountain. A candidate horizon has been identified approximately 300 meters below the surface and about 100 meters above the water table.

The design activities are being conducted in a manner to attempt to control and reduce to the extent practicable the impact exerted by the repository on the containment and isolation capability of the site. This process consists of careful iteration of design, analysis and interpretation of results to ensure long-term containment and isolation requirements are met and that short-term operations and costs are acceptable.
Colloid Generation and the Actinide Migration in Gorleben Groundwaters
Authors: Kim J.I. , Buckau G. , BaumgÄrtner F. , Moon H.C. , Lux D.
Published: March 2011

The generation and behaviour of realcolloids and pseudocolloids of the actinides, 238 pu, 241Am and 244Cm, are investigated in four different Gorleben Groundwaters. Colloids are characterized by ultrafiltration at different pore sizes from 1 nm to 450 nm and various analytical instrumentations. Behaviour of pseudocolloids has been analysed by determining their effects on the solubility and the distribution coefficient of actinides between groundwater and geomatrix. Sorption of actinide ions on groundwater-colloids (generation of pseudocolloid) are examined and the migration of actinides as pseudocolloids is discussed.
Geotechnical Materials Considerations for Conceptual Repository Design in the Palo Duro Basin, Texas
Authors: Versluis W. S. , Balderman M. A.
Published: March 2011

The Palo Duro Basin is only one of numerous potential repository locations for placement of a nuclear waste repository. Conceptual designs in the Palo Duro Basin involve considerations of the character and properties of the geologic materials found on several sites throughout the Basin. The first consideration presented includes current basin exploration results and interpretations of engineering properties for the basin geologic sequences.

The next consideration presented includes identification of the characteristics of rock taken from the geologic sequence of interest through laboratory and field testing. Values for materials properties of representative samples are obtained for input into modeling of the material response to repository placement. Conceptual designs which respond to these geotechnical considerations are discussed.
Geohydrology Surrounding a Potential High Level Nuclear Waste Repository in the Palo Duro Basin, Texas
Authors: Deyling M. A.
Published: March 2011

The Palo Duro Basin of the Texas Panhandle is being investigated as a potential high level nuclear waste repository site. Groundwater is the most likely mechanism for radionuclide movement, therefore, it is desirable to locate a repository in a hydrologic regime which is favorable for waste isolation and containment. The Palo Duro Basin consists of deep brine aquifers underlying a thick Permian age evaporite section. Overlying the Permian age evaporites are the Dockum and Ogallala fresh water aquifers.

Observed potentiometric data in the principal aquifers indicate a potential for downward flow from the surficial aquifers to the deep brine aquifers. Groundwater movement in these deep aquifers is very slow. Modeling efforts indicate flow times of hundreds of thousands to over a million years for groundwater to reach the basin margins.

Investigative methods have included drill-stem testing similar to oil field methodology, modified drill-stem testing with tools developed for low-permeability formations and long-term production tests similar to conventional water well pumping tests. Testing has generally indicated permeability of .1-10 millidarcies in the water transmitting units.
Review Panel Comments on Geomedia Specific Research:
Authors: Heath Colin A.
Published: March 2011

Mr. Chairman, members of the panel, my friends and colleagues. I want to thank you for the opportunity to attend this conference and to give you my impressions of the work reported here. My remarks today are those of a “now-outside” observer of the program but one who believes that the work of the program is absolutely essential for the continued use of nuclear power in this country and which, therefore, should be held to the highest standards of achievement. I think that many of you here will find some of my remarks to be somewhat controversial, or even provoking, but I offer them as an encouragement to proceed to meet the challenges of the program as expeditiously as possible. This program must succeed because nuclear power must be allowed to play an important role in providing electric power for this country.
Surface Layer Crystallization of Simulated Waste Glass at Elevated Temperatures
Authors: Inoue Tadashi , Yokoyama Hayaichi , Onchi Takeo , Kōyama Hiroaki
Published: March 2011

Surface crystallization was investigated for alkali borosilicate glass containing simulated waste of 26.4 wt% in the temperature range of 550 to 800°C. The crystals deposited on the surface layer of glasses were mainly composed of molybdates and molybdenum oxide. The saturated crystalline fraction of eash deposit, except for KMOO4, was maximum at 800°C in the temperature range investigated, and decreasing with decreasing temperature. The fractional change of crystallization was evaluated with the JMA equation. The activation energy of surface crystallization was estimated to be in the range of 50 to 70 kcal/mol for most of molybdates.
Longevity of Borehole and Shaft Sealing Materials: Characterization of Ancient Cement Based Building Materials
Authors: Langton Christine A. , Roy Della M.
Published: March 2011

Durability and long-term stability of cements in plasters, mortars, and/or concretes utilized as borehole plugging and shaft sealing materials are of present concern in the national effort to isolate nuclear waste within deep geological repositories. The present study consists of an examination of selected ancient building materials and provides insights into the durability of certain ancient structures. These data were combined with knowledge obtained from the behavior of modern portland cements and natural materials to evaluate the potential for longevity of such materials in a borehole environment. Analyses were conducted by petrographic, SEM, chemical, and x-ray diffraction techniques.
Cement-Based Waste forms for Disposal of Savannah River Plant Low-Level Radioactive Salt Waste
Authors: Langton Christine A. , Dukes Michael D. , Simmons Randolph V.
Published: March 2011

Defense waste processing at the Savannah River Plant will include decontamination and disposal of approximately 100 million liters of soluble salts containing primarily NaNO3, NaOH, NaNO2, NaAl(OH)4, and Na2SO4. A cement-based waste form, “saltstone,” has been designed for disposal of Savannah River Plant low-level radioactive salt waste. Bulk properties of this material have been tailored with respect to salt leach rate, permeability, and compressive strength. Microstructure and mineralogy of leached and unleached specimens were characterized by SEM and X-ray diffraction analyses, respectively. It has been concluded that the salt leach rate can be limited so that amounts of salt and radionuclides in the groundwater at the perimeter of the 100 acre disposal site will not exceed EPA drinking water standards.
In-Can Hot Pressing of Borosilicate Glass for the Immobilization of Highand Medium-Level Wastes
Authors: Ondracek G. , Toscano E.H.
Published: March 2011

The paper presents a method for the immobilization of different waste streams based in the uniaxial in-can hot pressing of a glass frit together with the waste oxides.

The process reported herein offers engineering simplicity in combination with many technological advantages such as significant decrease in temperature, use of small pressure, improved homogeneity of the products, production in easily arrangeable and interchangeable units. Furthermore, the proposed method has also proved to be suitable for treating intermediatelevel waste streams containing Zry-4 cladding fragments.
An Experimental and Modelling Approach of the Near Field Release and Transport Processes
Authors: Lanza F. , Saltelli A.
Published: March 2011

A simple mathematical model has been set up assuming that the glass leaching is defined by the diffusion and adsorption of the SiO2 in the porous media. It is also assumed that at the contact with the glass, the SiO2 content in the leachant reaches the saturation limit. Experimental weight losses seem to be in good agreement with the calculated values. In order to pass from the leaching rate of the glass to the release of radioactivity, the different radionuclides are subdivided into three different classes following their leaching rate and saturation limit. These three classes are discussed separately. An experiment which allows to measure leaching rate and diffusion of the various elements has been set up. Preliminary results are presented and discussed.
Methods of Simulating Low Redox Potential (Eh) for a Basalt Repository
Authors: Jantzen Carol M.
Published: March 2011

In the selection of a repository for burying vitrified nuclear waste, the leach rate of the waste form in groundwater is of concern. Basaltic groundwaters have inherently low redox potentials which may affect the waste form leach rate. Laboratory simulation of the Eh-pH conditions to be found in a basalt repository can be achieved when crushed basalt is added to deoxygenated deionized water. The effects of other redoxactive waste package components, such as iron, were found to stabilize solution redox potential at different valves under oxic and anoxic conditions. When iron was present, different waste form leach rates were observed with and without oxygen.
The Relationship Between Reaction Layer Thickness and Leach Rate For Nuclear Waste Glasses
Authors: Chick L. A. , Pederson L. R.
Published: March 2011

Three leaching tests, devised to distinguish among several proposed nuclear waste glass leaching mechanisms, were carried out for four different waste glasses. In the first test, the influence of a pre-formed reaction layer on elemental release was evaluated. In the second test, glass specimens were replaced with fresh samples halfway through the leaching experiment, to evaluate the influence of the concentration of glass components in leaching. Finally, regular replacement of the leachant at fixed time intervals essentially removed the variable of changing solution concentration, and allowed an assessment of the influence of reaction layer thickness on the leaching rate. Results for all glasses tested indicated that the reaction layer presented little or no barrier to leaching, and that most of the retardation on leaching rates generally observed are attributable to saturation effects.