bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Induced Defects in a-Si:H, Temperature Dependence of their Creation and Anneal and their effect on Photocarrier Lifetime
Authors: Stradins Paul , Fritzsche Hellmut , Tran Minh Q. 
Published: April 2011

ABSTRACTWe compared the effect of light soaking on the photoresponse and defect concentration ND of samples prepared by normal glow discharge, by remote plasma discharge, by the heated mesh and by the hot wire deposition methods. After exposure to 4×1027 cm−3 absorbed photons all samples have the nearly the same Np and photoresponse. At low temperatures additional defects with small anneal energies are created. Defects created at low temperatures were found to relax between 100K and 300K before they anneal. These new results cannot be explained by present models of defect creation. The kinetics of defect creation at low temperatures is discussed.
A Low Temperature Plasma-Assisted Deposition Process for Microcrystalline Thin Film Transistors, TFTS
Authors: He S.S. , Lucovsky G. 
Published: April 2011

ABSTRACTThe drive-current of low-temperature (∼300°C) deposited TFTs has been increased by replacing the a-Si:H channel, and source and drain materials with μc-Si. Lightly B2H6 doped, near-intrinsic μc-Si has been used as the channel layer of the TFTs, and n+ μc-Si was used for the source and drain contacts. The compensation of intrinsic defects in the undoped μc-Si by boron doping increases the dark conductivity activation energy from -0.35 eV to 0.8 eV. TFTs were fabricated in a bottom gate structure, and required an H2 plasma treatment to produce devices with effective channel mobilities of -6.8 cm2/V-s and threshold voltages of -3.7 V in the saturation region.
The Role of the Band GAP in the Light-Induced Degradation of Amorphous Silicon Alloys
Authors: Unold Thomas 
Published: April 2011

ABSTRACTThe dependence of the light-induced degradation on the band gap and hydrogen content in Amorphous silicon and related alloys is discussed. A simple model is presented which predicts that the light-induced degradation should be strongly correlated with the optical gap. In particular, for materials with Egap smaller than approximately 1.2eV no degradation is expected. The implications and consequences of the model for the task of reducing metastability in Amorphous silicon alloys are discussed.
Moving Photocarrier Grating Technique for Mobility and Lifetime Measurements in Amorphous Semiconductors
Authors: Hundhausen M. , Haken U. , Ley L. 
Published: April 2011

ABSTRACTIn this paper we describe a new method for the determination of the carrier lifetime (r) and the carrier Mobilities (μn, μp) in semiconductors. This technique utilizes a moving intensity grating that is generated by superposition of frequency shifted laser beams for the illumination of the sample. The Material parameters are extracted from the short circuit current in the sample induced by the moving grating as a function of it's velocity (vgr). We solve the continuity equations and Poisson's equation in the small signal approach for the modulated electron and hole densities and show how these densities result in an electric field that in turn acts on the electrons and holes in order to yield a short circuit current density jsc. From a fit of this expression for jsc to experimental data we determine μn, μp and τ.
Amorphous to Polysilicon growth and “Sunflower Effect” Observed in Catalytic-CVD
Authors: Matsumura Hideki , Hosoda Youichi , Furukawa Seijiro 
Published: April 2011

ABSTRACTPolysilicon films with a large mobility can be deposited at tempertures lower than about 400 °C by the catalytic chemical vapor deposition (cat-CVD) Method using a silane and hydrogen gas mixture. The mechanism of polysilicon growth and the structure of polysilicon itself are studied by TEM and X-ray diffraction. It is found that the polysilicon grows from an initial step of the deposition but that the grains start to orient preferentially along a (220) direction as the film grows. It is also found that such preferential axis of the grains is likely to orient toward a heated catalyzer as a sunflower always likes to face the sun.
Improved Electrical and Transport Characteristics of Amorphous Silicon by Enriching with Microcrystalline Silicon
Authors: Mireshghi A. , Hong W.S. , Drewery J. , Jing T. , Kaplan S.N. , Lee H.K. , Perez-Mendez V. 
Published: April 2011

ABSTRACTWe have deposited n-i-p diodes with microcrystalline intrinsic layers for radiation detection applications. The diodes show interesting electrical characteristics which have not been reported before. From TOF Measurement for our best samples we obtained μe values which are about 3 times larger than our standard a-Si:H. for μτ values approximately a factor of 2 improvement was observed. The N*D values derived from hole-onset measurements show lower ionized dangling bond density than normal a-Si:H Material. We have proposed a simple model which can very well explain the experimental results.
Interpretation of High Field Transport in A-Si:H Based on the Effective Temperature Definition
Authors: Nebel Christoph E. , Street R. A. 
Published: April 2011

ABSTRACTThe effective temperature definition which combines electric field and lattice temperature is critically discussed based on dark conductivity and drift mobility data measured over a wide range of temperature (10 K ≤ T ≤ 300 K) and electric field (102 V/cm ≤ F ≤ 6×105 V/cm). The reasonable values for the localisation lengths of electrons (αe ≡ 7–8 A) and holes (αh, ≡ 4 A) as well as the overall good agreement between predicted and deduced features support the effective temperature concept. A statistical transit time equation for transport at low temperature and high field is given and discussed based on time-of-flight data measured at T = 40 K.
Modeling of Reverse Bias Differential Charge Experiments in Amorphous Silicon
Authors: Shapiro Finley R. 
Published: April 2011

ABSTRACTAn analytic model is developed for differential charge measurements which avoids the use of the depletion approximation. In this experiment the incremental charge in the device is calculated as the difference between the total steady-state junction charge at two nearly equal voltages, similar to a very low frequency capacitance Measurement. All of the calculations, including an iteration to find the bulk Fermi level, can easily be performed using a spreadsheet program on a personal computer. It is shown that the results of these calculations agree extremely well with simulations performed with a complete numerical device simulator. Thus, the model useful for the analysis of experimental data
Charged Defect State Distributions Obtained from the Analysis of Photoconductivities in Intrinsic a-Si:H Films
Authors: Güneş Mehmet , Collins R. W. , Wronski C. R. 
Published: April 2011

ABSTRACTSteady-state photoconductivity, sub-bandgap absorption and electron spin resonance (ESR) Measurements were carried out on annealed and light soaked intrinsic hydrogenated Amorphous silicon (a-Si:H) films. The experimental results were modeled using detailed numerical Model. The defect densities derived from the sub-bandgap absorption in the light soaked films were correlated with the ESR spin densities. Selfconsistent fitting of the data was obtained using a gap state distribution which consists of positively charged defect states above, negatively charged defect states below and neutral defect states at about Midgap. Both the annealed and the light degraded states are modeled using the same distribution of gap states whose densities increase upon light soaking with a slight increase in the ratio of the neutral to charged defect densities. These results on intrinsic a-Si:H are consistent with those of charged defect Models.
Silicon Carbon Alloys Produced by VHF and Conventional PECVD. A Comparison of their Properties.
Authors: Crovini G. , Demichelis F. , Pirri C.F. , Tresso E. , Meier J. , Dub Ail S. , Shah A. 
Published: April 2011

ABSTRACTThe Very High Frequency (70 MHz) PECVD has recently proven its ability to produce Amorphous silicon with high deposition rates (10 Å/s) without affecting the quality of the Material. A comparative study of the optoelectronic properties of undoped silicon carbon alloys produced by Very High Frequency and by conventional RF (13.56 MHz) is carried out. Conductivity, infrared absorption, optical transmission and deep defect densities via PDS and ESR have been Measured. Deposition parameters under study aie methane fraction and hydrogen dilution. In contrast to conventional PECVD, we observe for VHF depositions an increase of the deposition rate with the addition of Methane. Larger energy gap and smaller Urbach energy values seem to indicate a better incorporation of carbon in the VHF case. A study of the degradation induced by light is also presented.
Nanoscale Study of the Hydrogenated Amorphous Silicon Surface
Authors: Tanenbaum D.M. , Laracuente A. , Gallagher A.C. 
Published: April 2011

ABSTRACTA scanning tunneling microscope has been used to study the topology of the surface of device-quality, hydrogenated Amorphous silicon deposited by rf discharge from silane or “hot wire” CVD. The substrates were oxide-free single-crystal silicon or GaAs. Films studied were either grown in our laboratory and observed with no air exposure, or grown at other laboratories producing device-quality photovoltaic cells and viewed after air exposures of less than 30 Minutes. Thin films (10 nm) representing early growth stages appear significantly smoother than the thicker films. The topology of thick films (> 50 nm) has large variations over individual samples. While many regions can be characterized as “rolling hills”, atomically flat areas are sometimes observed nearby in our films. In most regions the observed slopes were 10% or less from the horizontal, but some steep-sided valleys, indicating incipient voids, are seen. Overall surface roughness measured on sub-Micron areas of our films is very inhomogeneous. Uniformity of the films grown off site was much better, although no atomically flat regions were observed, surface roughness can be estimated.
Boron Doped A-Si,C:H Grown by Reactive Magnetron Sputtering from Doped Targets
Authors: Liang Y.H. , Yang S.-Y. , Nuruddin A. , Abelson J.R. 
Published: April 2011

ABSTRACTWe have deposited p+ a-Si,C:H films by reactive magnetron sputtering from boron doped target with 1 at.% B. We have investigated the influence of H2 pressure on the electrical and microstructural properties of the doped a-Si,C:H films. The boron concentration in the film is ∼2–4×1020cm−3. The incorporation of B atoms decreases by a factor of 2 at the highest H2 pressure. We have obtained films of Taue bandgap ∼1.8–1.84eV with dark conductivity 2–8×10− 6Ω−1cm−1, thermal activation energy ∼0.28–0.33eV and νμτe ∼1–3×10−8cm2/V. This result is comparable with glow discharge B doped a-Si,C:H film. We discuss the film Microstructure, as reflected in infra-red & thermal H evolution spectra, vs. the absolute composition of sputtered boron doped a-Si,C:H films.
Excimer Laser Annealing of Amorphous Silicon Films
Authors: Viatella J. , Singh R.K. , Thakur R.P.S. 
Published: April 2011

ABSTRACTLow temperature processing is necessary for the fabrication of thin-film transistors for electronics-on-glass applications, including active matrix flat-panel displays. One method to achieve this involves the use of pulsed excimer-laser annealing of an Amorphous silicon layer on top of an SiO2 layer. The intense UV laser is absorbed in the Amorphous silicon region, Maintaining a low average temperature. The thickness of the underlying SiO2 layer affects the solidification velocity and hence the grain size of the annealed layer. Previous work has concluded that the resultant grain size is small (<100 nm) and further work is needed in finding ways of increasing grain size. This paper describes how grain size is affected by varying the thickness of the SiO2 layer. Correlations will be discussed.between the solidification velocities and grain size as affected by the varying thickness of the SiO2 layer. The paper includes a comparison between experimental and theoretical results, using equations based on energy balance considerations.
Efficient Visible Room Temperature Photoluminescence in Wide Gap Hydrogenated Amorphous Silicon-Carbon Alloys
Authors: Tessler Leandro R. , Solomon Ionel 
Published: April 2011

ABSTRACTWe report a photoluminescence study on amorphous hydrogenated silicon carbon (a-Si1-xCx:H) alloys with carbon concentration in the range O < x < 0.5, prepared by PECVD in the “low-power” regime, that preserves the tetrahedral coordination of the carbon atoms. These samples have optical gaps higher than conventional “high power” alloys with the same carbon content. For carbon concentrations below x = 0.2 the photoluminescence behaves essentially as in pure a-Si:H with increased gap, Urbach energy and DOS. For higher carbon concentrations there is a change in the recombination process, that we attribute to a change in the dominating diffusion process of the photogenerated carriers. The integrated photoluminescence intensity for carbon-rich samples is very weakly dependent on the temperature, and at room temperature it approaches that of pure a-Si:H at 77K. For all samples, the photoluminescence bandwidth can be well described by a zero-phonon model.
Photobleaching of PL and Temperature Dependence of ESR in Nitrogen-Rich Amorphous Silicon Nitride Films
Authors: Chen D. , Viner J.M. , Taylor P.C. , Kanicki J.Z. 
Published: April 2011

ABSTRACTWe report measurements in nitrogen-rich a-SiNx:H (x > 1.3) of visible light photobleaching of photoluminescence (PL) that has been fatigued with UV light. We also review the temperature dependence of electron spin resonance (ESR) from a-SiN1.6:H films. The samples were prepared by plasma-enhanced chemical vapor deposition (PECVD) at 400 and 250° C. The optical gap of a-SiN1.6:H is about 5 eV. In PL experiments, the PL intensity fatigues under UV excitation, finally reaching a saturated value. By illuminating with visible light, the UV effect is partially bleached, that is, the PL intensity is partially restored. The bleaching light ranges in energy from 2.0 to 4.8 eV. With increasing bleaching-light energy, the reinduced PL intensity increases, reaches a maximum at a bleaching energy of 3.8 eV, and then quickly decreases. In ESR experiments, there exists a small ESR signal in as-deposited films before UV excitation and the variation of the ESR signal with temperature is similar to that of a-As.
Modelling Heteroface of P.I.N Solar Cells for Improving Stability
Authors: Fantoni A. , Vieira M. , Martins R. 
Published: April 2011

ABSTRACTThe introduction into a traditional p.i.n structure of two defective buffer layers near the p/i and i/n interfaces can improve the device stability and efficiency through an enhancement of the electric field profile at the interfaces and a reduction of the available recombination bulk centers. The defectous layer (“i'-layer”), grown at a higher power density, present a high density of defects and acts as “gettering centers” able to tailor light induced defects under degradation conditions. If the i-layer density of states remains below 1016 eV−1 cm−3 and assuming a Gaussian distribution of defect states, the gettering center distribution will not affect significantly the carrier population but only its spatial distribution.We report here about a device numerical simulation that allows us to analyse the influence of the “i'-layer” position, thickness and density of states on the a-Si:H solar cells performances. Results of some systematic simulation from the ASCA program (AMorphous Solar Cell Analysis), and for different configurations will be presented.
A Study of a-Si:H/a-SiGe:H Tandem Solar Cells and Modules
Authors: Li Yuan-Min , Yang L. , Bennett M.S. , Chen L. , Jackson F. , Rajan K. , Arya R.R. 
Published: April 2011

ABSTRACTWe report a study of a-Si:H/a-SiGe:H dual-bandgap p-i-n type tandem solar cells and Modules. Refined bandgap grading in the a-SiGe:H bottom cell results in higher Jsc (higher red response) without loss in FF or Voc. IMprovements in the tunnel junction consisting of doped widegap a-SiC:H and μC-Si lead to higher FF and lower optical loss. Undoped widegap a-SiC:H is used as interface layers in the top junction. Initial conversion efficiencies of 11.4% and 10.5% have been obtained for small-area cells and one-square-foot modules, respectively. The double junction cells and modules exhibit good stability and saturation of light-induced degradation, showing only ∼15% decrease in conversion efficiency after more than 1000 hours of simulated AM1.5 illumination. The stabilized efficiencies are 9.6% and 9.1%, respectively, for small area cell and large area Module. We also present some findings from the computer simulations of multijunction solar cell performance using a simple lump-circuit device Model.
Effects of TCO/a-Si:C:H Interface Defect States on p-i-n a-Si:H Solar Cell Performance
Authors: Smole Franc , Topič Marko 
Published: April 2011

ABSTRACTTo explain realistic circumstances with regard to energy band profiles at the TCO/a-Si:C:H heterojunction, the ASPIN computer simulation has been used. Numerical calculations indicate that the increased interface defect densities result in a steep potential drop inside the interface region, while the rest of the work function difference extends into the p-layer. The detrimental effect of a-Si:C:H partial oxidation has been simulated by additionally increased density of states at a-Si:C:H surface, and its influence on the potential barrier has been analyzed. The impact of both TCO/a-Si:C:H interface states and a-Si:C:H surface states on the photoelectric properties of p-i-n a-Si:H solar cell is discussed, and a possible improvement of Voc is envisaged.
VHF Coaxial Helix Plasma Source for a-Si:H
Authors: Stephan U. , Kuske J. , Schade K. 
Published: April 2011

ABSTRACTCoaxial helical resonators are used in the field of high frequency engineering for narrow band selection of signals from about 10 MHz to 500 MHz (VHF and low UHF range) [1, 2]. Their favorable geometric construction suggests their utilization as plasma source for etching and deposition of a-Si:H at frequencies between 30 and 200 MHz - an additional, but still unusual application.The resonator consists of a cylindric outer conductor, which is closed on one side by a bottom plate, and a rotationally symmetrical inner conductor of spiral form (helix) Measuring γ/4. One end of the helix is grounded to the bottom plate (short circuit), the other end is open (open circuit). Power supply is feasible either galvanically by connecting to the helix or inductively by means of a coupling coil. Applying a suitable coupling factor allows operation at resonance without matchbox. The plasma is generated within the resonator and above its open end, which can be adjusted to special conditions of application with the aid of several grids. In contrast to the source commonly used, the coaxial helix plasma source has proved advantageous with regard to simple design, easy mounting, Minimal outer electrical equipment, no dependence of generated plasma on substrate measures, good breakdown and discharge behavior, low supply voltage (some tens of volts), high power density, and, due to a discharge occurring without filament, also to life durability and no thermally generated particle emission. The application of very high frequencies leads to a low ion bombardment intensity of a-Si:H, and thus additional magnetic fields are not necessary.
A Large Area, High-Resolution a-Si:H Array for X-Ray Imaging
Authors: Antonuk L.E. , El-Mohri Y. , Huang W. , Siewerdsen J. , Yorkston J. , Street R.A. 
Published: April 2011

ABSTRACTThe development of a large area, high-resolution, a-Si:H x-ray imager is reported. The array has 1536×1920 pixels, a pixel pitch of 127μm, and an area of 19.5×24.4 cm2. Tne array is tailored to the high frame rate and high spatial resolution requirements of diagnostic x-ray imaging. The design of this array is presented and examples of x-ray images are illustrated. Initial Measurements of the sensor capacitance and pixel time constant properties are in good agreement with theoretical expectations. These results indicate that high-resolution arrays of this construction are capable of providing fluoroscopic images at rates of at least 30 frames per second.
Technology and Performance of TFA (

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SIC-Sensors
Authors: Fischer H. , Schulte J. , Rieve P. , Böhm M. 
Published: April 2011

ABSTRACTA TFA image sensor consists of an amorphous silicon based multilayer structure on top of a crystalline ASIC. The Multilayer acts as the optical detector, whereas the ASIC performs analog or digital signal processing for each individual pixel. Depending on the operation Mode, the dynamic range of the detector exceeds the performance of conventional CCDs by far. Pixel electronics which is adapted to the requirements of the detector can thereby maximize the dynamic range of the complete sensor array. Crosstalk among adjacent pixels can be eliminated by technological or electronic Means.
“Thick” a-Si:H P-i-n diodes, produced by the VHF-GD process: spectral response for visible/infrared light and current transients
Authors: Chabloz P. , Keppner H. , Fischer D. , Wyrsch N. , Shah A. 
Published: April 2011

AbstractWith the possibility to deposit thick amorphous silicon layers, applications like particle- or X-ray detectors can be envisaged. The present paper describes new results obtained with a series of thick p-i-n diodes produced by VHF-GD (Very High Frequency Glow-Discharge). The goal is to obtain the maximum output signal for given detection conditions (reverse voltage, generation rate,…). The problem of the collection of the electrons and holes is discussed in this paper, in relation with the distribution of the electric field. As is well known, trapped charges screen the inner part of the intrinsic layer of the detector. Due to this effect, even under strong reverse bias-voltage, a complete depletion of the whole intrinsic layer can in general not be obtained for thick diodes; however, even if the diode is not completely depleted, the signal increases with increasing diode thickness until a maximum is reached for the signal, and then it decreases again. Finally, different rise-times of the transient current (current after a jump in bias voltage is applied) have been Measured. Differing between one diode and the other, the rise-time of the transient current was found to vary between 0.1 seconds and 1 hour; a clear dependence on the deposition conditions is observed. Long rise-times are major difficulty to be removed, because most of the applications like imaging require short response time of the detector.
Improvement of film Quality of A-Si:H Deposited by Photo-CVD using SiH2Cl2
Authors: Oshima T. , Yamaguchi K. , Yamada A. , Konagai M. , Takahashi K. 
Published: April 2011

ABSTRACTHydrogenated Amorphous silicon films (a-Si:H) were prepared by mercury sensitized photo-CVD using SiH4 and SiH2Cl2 gas mixture. The effects of chlorine (Cl) on the electrical, optical and structural properties of the a-Si:H films were investigated. It was found that a small addition of SiH2Cl2 to the deposition system increases the photo-sensitivity, decreases the defect density, and reduces the light induced degradation of a-Si:H films. At a large addition of SiH2Cl2, however, the CI incorporation into the films was observed, resulting in the deterioration of the film properties. The electrical and optical properties were successfully improved by the H2 dilution when the films were deposited with a large addition of SiH2Cl2.