bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of Storage Spatial Light Modulators Incorporating Amorphous Silicon as Photoconductor
Authors: Slobodin D. , Sugiarto D. , Bone M. , Kahn F. 
Published: March 2011

ABSTRACTThe behavior of a-Si.H photoconductors under conditions used in storage photoaddressed spatial light modulators (PASLM) is described. The differences observed in high and lov voltage operation are explained in terms of charge collection efficiency. A voltage dependent resistance term is proposed for PASLM modelling. The effects of photocapacitance are assessed and found to be of significance only under conditions of low drive voltage and higher illumination levels.
Study of a-Si:H/μc-Si:H Heterojunction as Photosensor for Large Screen Projection Display
Authors: Han Weiqiang , Han Gaorong , Qiao Jianmin , Du Pija , Zhao Danmei , Ding Zishang 
Published: March 2011

ABSTRACTLiquid crystal light valve(LCLV) using an a-Si:H/μc-Si:H heterostructure as the photosensor and the nematic liquid crystal as the modulator has been firstly presented for large screen projection display. The a-Si:H photoconductor and μc-Si:H light blocking layer were prepared by a modified glow discharge CVD method. The optoelectric and structure properties of the μc-Si:H films deposited at different deposition conditions have been studied. The a-Si:H film and the continuously deposited pc-Si:H film possibly form an a-Si:H/μc-Si:H heterojunction. The electrical and optoelectric properties of the heterojunction has been studied.LCLV using a-Si:H/μc-Si:H heterostructure has shown that the most aspects of the device performance can be improved.
Amorphous Silicon Image Sensor Arrays
Authors: Powell M J , French I D , Hughes J R , Bird N C , Davies O S , Glasse C , Curran J E 
Published: March 2011

ABSTRACTWe have developed a technology for 2D matrix-addressed image sensors using amorphous silicon photodiodes and thin film transistors. We have built a small prototype, having 192×192 pixels with a 20μm pixel pitch, and assessed its performance. The nip photodiodes can have dark current densities of less than 1011 A.cm-2 (up to 5V reverse bias) and peak quantum efficiencies of 88% (at 580nm). We operated the sensor in real time mode at high speed (50 Hz frame rate and 64μS line time). The image sensor has a low noise performance giving a dynamic range in excess of 104. The maximum crosstalk is about 2%, which allows at least 50 grey levels. The bottom contact of the photodiode acts as a light shield from light through the substrate, which enables the sensor to be operated as an intimate contact image sensor to image a document placed directly on top of the array. In this mode, the CTF was 75% at 2 lp.mm1. Good quality images are demonstrated in both front projection and intimate contact imaging modes.
Dependence of 1.00 MeV Proton Radiation Resistance of a-Si:H Alloy Solar Cells on Cell Thickness
Authors: Woodyard James R. 
Published: March 2011

ABSTRACTRutherford bacJcscattering spectrometry has been used to determine the role of thickness and composition on the radiation resistance of a-Si:H based alloy solar cells. Single and dual-junction cells with thicknesses between about 0.23 and 1.1 microns were studied. Cells were irradiated with 1.00 MeV protons using fluences between 1E13 and 1E15 cm-2; the radiation resistance was determined using J-V measurements. The fluences produced significant changes in Jsc. Cells with thicknesses in the 0.23 to 0.69 micron range degraded about the same when irradiated with the same fluences; thicker single-junction cells degraded with both thickness and fluence. Thirty percent Ge in a-Six,Ge1-x:H cells results in poorer radiation resistance. It appears that Ge is more effective than Si in stabilizing 1.00 MeV proton-induced defects.
Pulsed Laser Crystallization of Amorphous Silicon Films: Effects of Substrate Temperature and Laser Shot Density
Authors: Johnson R. I. , Anderson G. B. , Ready S. E. , Fork D. K. , Boyce J. B. 
Published: March 2011

ABSTRACTA recent report on pulsed laser crystallization of a-Si thin films concluded that substrate bias temperatures up to 400°C in combination with laser fluences below 500 mJ/cm2 had little effect on grain size and transport properties. The current report describes the effects of substrate bias temperature up to 500°C and laser fluence up to 540 mJ/cm2 on grain size, mobility and Si (111) x-ray peak intensities. Results indicate that substrate bias temperatures above 400°C, in combination with high laser shot densities and large laser beam spot energies (> 500 mJ/cm2), are a factor in Improving these film properties.
Analysis of VHF Glow Discharge of A-SI:H Over a Wide Frequency Range
Authors: Zedlitz Ralf , Heintze Moritz , Bauer Gottfried H. 
Published: March 2011

ABSTRACTa-Si: H was deposited in a VHF-plasma in a wide frequency range up to 250MHz. The deposition rate was found to increase with excitation frequency up to 180MHz, where values of 35Å are achieved maintaining good film propertiesThe onset of this increase occurs near 60MHz, when the excitation frequency exceeds the inelastic electron-neutral collision rate. From optical emission of hydrogen and a He/Ar line pair the high energy tail of EEDF was probed. It is found, that the rise in deposition rate is solely due to the increased plasma density and not to an enhancement of the high energy tail of the EEDF, as postulated previously.
Microstructure and Dangling Bond Defects in Amorphous Hydrogenated Silicon Deposited Near Room Temperature
Authors: Cheung Man Ken , Petrich Mark A. 
Published: March 2011

ABSTRACTThe microstructure of high-density amorphous hydrogenated silicon (a-S.i:H) films deposited at 50°C substrate temperature was revealed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies to be similar to that of “device-quality” a-Si:H films deposited at standard “optimum” conditions. However, optical absorption measurements of these low microstructure 50°C films with photothermal deflection spectroscopy indicate that they have higher densities of gap state defects and localized band tail states than “device-quality” films deposited at standard substrate temperatures. The correlation between the amount of microstructure and electronic properties is not unique. A low amount of microstructure is a necessary, but not sufficient, requirement for high electronic quality a-Si:H films.
Small-Angle X-Ray Scattering Studies of Glow-Discharge-Produced a-SiGe:H Alloys
Authors: Jones Scott J. , Chen Yan , Williamson D. L. , Mooney G.D. 
Published: March 2011

ABSTRACTElectron density fluctuations associated with microstructural features on a scale from about 1 to 25 nm in glow-discharge-deposited a-Si1-xGex:H films were studied by the technique of small-angle x-ray scattering (SAXS). Films prepared in four different deposition systems (in different laboratories) have been characterized and a general increase in the SAXS signal with increasing x is observed. Density deficiencies determined from film flotation measurements lead to the correlation of the increased scattering intensities with increases in the volume fractions of micro voids. Modeling of the data yields void size distributions that demonstrate significantly more of the larger voids (2 to 6 nm) than found at x=0 (around 1 nm). For the alloys with x>0.4, the scattering at the smallest angles was observed to decrease substantially upon tilting of the sample relative to the x-ray beam. This result contrasts with the small or no changes in SAXS upon tilting device-quality x=0 films. This anisotropie scattering associated with the tilting experiments has been modeled with distributions of ellipsoidal microvoids that are preferentially oriented with their major axes normal to the film plane. This latter result is consistent with a columnar-like microstructure. However, one film with x=0.37 shows no evidence for such microstructure.
Bond-Angle Variation and Microstructure in Hydrogenated Amorphous Silicon
Authors: Berntsen A. J. M. , Van Den Boogaard M. J. , Van Sark W. G. J. H. M. , Van Der Weg W. F. 
Published: March 2011

ABSTRACTA series of hydrogenated amorphous silicon (a-Si:H) films was deposited by rf glow-discharge deposition using various processing conditions. We have studied microstructure in the films by means of infrared absorption spectroscopy. Small-angle X-ray scattering measurements were used to determine the microvoid fractions of a few selected samples. Our results show that both the void fraction and the amount of microstructure can be varied either by changing the substrate temperature or by H2 dilution. Bond-angle variation in the films was probed by Raman scattering measurements. The Raman data indicate that the substrate temperature is the main variable that determines the bond-angle variation. We conclude that the presence of microvoids in a-Si:H does not influence the structural disorder of the amorphous matrix surrounding the voids. Our results are in agreement with experimental work on microvoids in a-Si1-xCx:H, and model calculations on voids in a-Si.
Small-Angle X-Ray Scattering from a-Si:H and a-SiC:H Alloys Prepared by Reactive DC Magnetron Sputtering
Authors: Chen Yan , Jones S.J. , Williamson D.L. , Yang S. , Maley N. , Abelson J.R. 
Published: March 2011

ABSTRACTThe microstructure of amorphous silicon-based alloys prepared by reactive magnetron sputter (RMS) deposition has been examined on a scale from 1 to 25 nm using small-angle x-ray scattering (SAXS) and compared to that from films prepared by standard glow-discharge (GD) technology. Device-quality RMS a-Si:H material is found to have a larger microvoid fraction than device-quality GD a-Si:H and to have a significantly different size distribution. Addition of by the RMS technique using CH produces enhanced SAXS similar to the introduction of C via CH4 in GD material. A significant difference in the SAXS from RMS a-Si:H and a-SiC:H films compared to GD films is the observation of some oriented microstructure, most likely columnar in nature. Flotation density measurements of the same films examined by SAXS support the assumption that the SAXS originates primarily from microvoids.
Evidence for Hydrogen-Hydrogen Interactions During Diffusion in a-Si:H
Authors: Jackson W. B. , Tsai C.C. , Santos P. V. 
Published: March 2011

ABSTRACTThe effects of H concentration on H transport has been measured by deuteration of H depleted samples which were re-hydrogenated at various concentrations and on samples subjected to various annealing protocols. A remarkable observation is that the trap density appears to increase with H concentration. Extended thermal annealing appears to increase the trap depth but does not markedly alter the number of traps. The results suggest that H introduced from the plasma is less strongly bound than H residing in the film during annealing. Nucleation and growth of H clusters is introduced as a possible model accounting for these transport results.
Defect Equilibration and Stabilization in Two Types of Low-Spin-Density a-Si:H
Authors: McMahon T.J. 
Published: March 2011

ABSTRACTRelaxation data provide evidence that thermally generated defects with spin observed in thick, undoped hydrogenated amorphous silicon (a-Si:H) films can be stabilized with alternate structural configurations. Some quenched-in metastable spins, equilibrating further at a lower temperature, relax and become more resistant to annealing. Some of these defects take longer to anneal than any of the defects equilibrated only at the higher temperature. An obvious crossing of annealing data curves occurs on one of two differently prepared films. Crossover has important physical implications in deciding between defect models.Such an observation necessitates the use of defect models with more complexity than variations based on two-level energy-configuration coordinate diagrams. Long annealing times may not be controlled simply by high energy barriers; the annealing of a spin may require many dispersive steps with smaller energy barriers. Models that stablize a spin by either hierarchically constrained defect configurations or the trapping of a mobile hydrogen in a distribution of sites can be used to explain this result. The fact that crossover is more obvious on the sample that has an oriented microstructure implicates film structure.
Macro-Trench Studies of Surface Reaction Probability of a-Si:H Film Growth
Authors: Nuruddin A. , Doyle J. R. , Abelson J. R. 
Published: March 2011

ABSTRACTUsing a “macro-trench” technique, the surface reaction probabilities β of the a-Si:H growth precursors for remote hollow cathode silane discharge (HC) and reactive magnetron sputter deposition (RMS) are measured. Both deposition methods produce state of the art photo-electronic quality a-Si:H. For the HC case, β= 0.28 ± 0.05, whereas for RMS deposition β ≈ 0.97 ± 0.05. We conclude that β is not universally correlated with film quality, and discuss mitigating factors present in RMS deposition that permit high quality film to be deposited despite the high film precursor reactivity.
A Defect Density of ∼ 1014 cm-3 in Hydrogenated Amorphous Silicon Deposited at High Substrate Temperatures
Authors: Ganguly Gautam , Matsuda Akihisa 
Published: March 2011

ABSTRACTThe idea of surface mobility of growth precursors determined material quality has been exploited by raising the substrate temperature above the conventional 250°C and the ensuing thermal depletion of the surface hydrogen coverage compensated by increasing the precursor flux (deposition rate) to prepare ultra low defect density hydrogenated amorphous silicon.
The Influence of the Void Structure on Deuterium Diffusion in a-Si:H
Authors: Van Den Boogaard M. J. , Jones S. J. , Chen Y. , Williamson D. L. , Hakvoort R. A. , Van Veen A. , Van Der Steege A. C. , Bik W. M. Arnold , Van Sark W. G. J. H. M. , Van Der Weg W. F. 
Published: March 2011

ABSTRACTWe have used small-angle X-ray scattering (SAXS) and Doppler-broadening measurements of positron-annihilation radiation to study changes in the microvoid distribution in PECVD a-Si:H films during annealing. From a comparison of data on deuterium diffusion with information obtained from SAXS we conclude that changes, during annealing, in the dispersive character of deuterium diffusion are likely to be caused by void formation through clustering of smaller structural defects.
New Results on Enhanced Deuterium Diffusion Under Illumination in Amorphous Silicon
Authors: Branz Howard M. , Asher Sally E. , Nelson Brent P. 
Published: March 2011

ABSTRACTWe measure the light-enhancement of D diffusion in hydrogenated amorphous silicon and determine that the mechanism for the effect is an increase of the rate of Si-D bond breaking under illumination. We exclude light-induced heating of the sample and light-induced excitation of D between dissimilar materials as sources of the light-enhancement. It is a bulk effect, most likely caused by excess carriers. We are able to observe the light-induced effect with 380 mW-cm-2 of red light, an intensity only slightly larger than the intensity normally used to induce the Staebler-Wronski effect. At room temperature, the effect is unobservable and we derive an upper bound of 2 × 10-8 photon-1 for the efficiency of light-induced Si-D bond breaking. Implications for the Staebler-Wronski effect are discussed.
Lithium Stability and Diffusion In a-Si:H
Authors: Beyer Wolfhard , Herion Jörg , Hagner Heribert , Zastrow Uwe 
Published: March 2011

ABSTRACTSIMS measurements of implanted Li in (doped and undoped) a-Si:H, a-Si and a-Si:H alloys are discussed. The results suggest basically the same Li diffusion process in p- and n-type a-Si:H with negatively charged acceptors or dangling bonds acting as traps for the positively charged diffusing Li ions. Li is less stable in a-Si than in a-Si:H; Li stability in a-Si:H is enhanced at high concentrations of implanted Li. Both diffusion and stability are modified by doping gradient-related electric fields.
The Role of Charged Defects in Photo-Degradation of Hydrogenated Amorphous Silicon
Authors: Dalal Vikram L. , Chopra Sanjiv , Knox Ralph 
Published: March 2011

ABSTRACTWe examine the role of charged defects in inducing degradation of electronic properties of a-Si:H upon exposure to light. We measure the kinetics of decay of photo-conductivity of a-Si:H films at different light intensities, and the corresponding changes in mid-gap optical absorption. We find that the initial, rapid decay of photo-conductivity can be modeled guite well by invoking Adler's model of conversion of charged defects to neutral dangling bonds(D- to D° conversion). A consequence of this conversion is a decrease in sub-gap absorption upon photo-induced degradation, which we observe. Therefore, we conclude that charged defects coexist with neutral defects in a-Si:H, and they play a major role in early stages of photo-degradation.
Isolation of Temperature Effects on the Kinetics of Light Induced Defect Generation in a-Si:H
Authors: Benatar L. , Grimbergen M. , Fahrenbruch A. , Lopez-Otero A. , Redfield D. , Bube R. 
Published: March 2011

ABSTRACTData are presented here that show the effects of temperature on the kinetics of metastable defect formation in undoped a-Si:H over the range 45°-110°C. CPM (Constant Photocurrent Method), photoconductivity, and dark conductivity measurements were made and provide independent checks of the defect generation behavior. A stretched exponential description of defect formation as a function of time was used to fit the CPM defect density data. The stretched exponential time constant, τSE, is thermally activated with an apparent activation energy of 1 eV, a value that agrees well with data for defect anneal and solar cell degradation. The data indicate that thermal terms are not negligible for temperatures as low as 45°C, and therefore should be included in any model of the kinetics of defect formation. The role of adistribution of anneal energies and the regimes of dominance of thermal and optical rate terms are discussed in the context of the model.
Current Induced Degradation of a-Si:H Pin and Schottky Switches
Authors: Nieuwesteeg K.J.B.M. , Boogaard J. , Oversluizen G. 
Published: March 2011

ABSTRACTForward-bias current stress experiments were performed on α-Si:H p-i-n and Schottky switches at several temperatures and at current densities up to 6 A/cm2. In Schottky diodes, current stressing results in a lowering of the forward-bias SCLC current together with an increase of its thermal activation energy. The reverse current is unaffected. The rate of degradation of the forward current increases with increasing temperature. From a comparison of the degradation behaviour of Schottky's with different barrier height we find that the rate of degradation is correlated to the minority-carrier injection ratio of the Schottky contact. The effects are interpreted as being due to metastable state creation in the bulk α-Si:H. The rectifying properties of the metal-to-semiconductor contact are relatively stable to current stress.The forward-bias I-V curves of p-i-n diodes degrade much faster than those of the Schottky switches. At the same time, the reverse-bias current increases due to the stress. The lower stability to current-stress of p-i-n diodes is ascribed to the much higher hole injection in the mesa. After a short time, the reverse-bias current becomes dominated by e-h generation from the created deep states in the i-layer and then gives a direct indication of its time dependence.
Growth of Ge/Si Amorphous Superlattices by Dual-Target DC Magnetron Sputtering
Authors: Järrendahl K. , Birch J. , Hultman L. , Wallenberg L.R. , Radnoczi G. , Arwin H. , Sundgren J-E. 
Published: March 2011

ABSTRACTAmorphous Ge/Si superlattices have been grown by dual-target dc magnetron sputtering at ambient temperature under different negative substrate bias voltages Vs. The films were studied with cross-sectional transmission electron microscopy (XTEM). All films were amorphous, but for Vs ≤ 110 V the superlattices exhibited a columnar structure. Within each column, the compositional modulation was clearly resolved except in the vicinity of the column boundaries. For 110<VS≤250V, dense films with homogeneous and well-defined layers were obtained. High-resolution XTEM studies showed that superlattices with individual layer thicknesses less than 1.5 nm and smooth interfaces could be fabricated. Increasing Vs > 250 V resulted in ion induced intermixing such that at Vs ≥ 450 no compositional modulation was observed. The obtained structural results are discussed in terms of available models for ion-irradiation effects during low-temperature ballistic growth.
Energy Differences Between the Si and the Ge Dangling Bond Defects in a-Si1-xGex Alloys
Authors: Cho S.M. , Davidson B.N. , Lucovsky G. 
Published: March 2011

ABSTRACTWe have investigated the difference in the electronic energies of neutral Si and Ge dangling bond states in undoped a-Si1-xGex alloys as a function of the alloy composition, x, and local bond-angle distortions. The local density of states, LDOS, in a-Si1-xGex alloys has been calculated using nearest-neighbor interactions, and employing the Cluster Bethe Lattice method. We conclude that for ideal, tetrahedrally bonded amorphous semiconductors alloys, the Ge dangling bond energy is lower than that of Si dangling bonds by ∼ 0.13 eV, independent of the specific nearest neighbors to the dangling bond (3 Si-atoms, 2 Si-atoms and 1 Ge-atom, etc.), but that the spread in dangling bond energies associated bond-angle variations of the order of 6–8 degrees can be larger than this energy difference (∼0.3 eV or greater). This means that structural disorder, rather than chemical disorder causes Si and Ge-atom dangling bond states to overlap in their energy distributions.
Defect Saturation in a-SiGe:H(F) Alloys
Authors: Wang N.W. , Morin P.A. , Chu V. , Wagner S. 
Published: March 2011

ABSTRACTIt is a question as yet unresolved whether the density of light-induced defects in a-Si:H reaches a saturated value that cannot fundamentally be exceeded, or whether the defect density is in all conditions a steady-state value that reflects carrier concentration and temperature. In our experiments on a-Si:H we have observed defect saturation at low temperature and high light intensity; on the other hand, data exhibiting no saturation have also been published. To learn more about this question we have carried out saturation experiments on a-SiGe:H(F) alloys. These alloys have lower defect freeze-in temperatures than a-Si:H and, presumably, lower annealing energies. Therefore, saturation should be more difficult to achieve in the alloys than in a-Si:H.We have studied saturation for a-SiGe:H(F) samples to temperatures above the onset of thermal annealing and have observed that its behavior is similar to that seen in a-Si:H.
Optical Properties of Hydrogenated Amorphous Silicon, Silicon-Germanium and Silicon-Carbon Thin Films
Authors: Dawson R.M. , Li Y.M. , Gunes M. , Heller D. , Nag S. , Collins R.W. , Wronski C.R. , Bennett M. , Li Y.M. 
Published: March 2011

ABSTRACTThe optical properties of solar cell grade hydrogenated amorphous silicon (a-Si:H), silicon germanium (a-SiGe:H) and silicon carbon (a-SiC:H) alloy thin films have been investigated over a wide photon energy range (0.8–4.8 eV) using a combination of subgap photoconductivity, reflection and transmission, and spectroscopie ellipsometry techniques in order to obtain accurate optical functions for solar cell modelling. Studies on films with thicknesses ranging from a few hundred Å to a few microns show that the optical spectra obtained by the different techniques agree closely over the energy ranges of overlap and display no thickness dependence from the Urbach tail energies and above. Thus, the results appear to be free of measurement and sample related artifacts. Three different methods provide a common value for the optical gap within ±0.02 eV and the result for a-Si:H is ∼0.1 eV below the mobility gap.