bluuebunny/crossref_metadata_2025_split 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTTwo 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

ABSTRACTThe 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

ABSTRACTSix 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

ABSTRACTPulsed 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTRecent 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

ABSTRACTWe 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

ABSTRACTLight-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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTSmall 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

ABSTRACTWe 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

ABSTRACTWe 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

AbstractThe 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

ABSTRACTWe 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

ABSTRACTThe 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

ABSTRACTMicrocrystalline 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

ABSTRACTThe 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

ABSTRACTUsing 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.