bluuebunny/crossref_metadata_2025_split huggingface dataset:
Injection Doping of Ultrathin Microcrystalline Silicon films Prepared by CC-CVD
Authors: Koynov S. , Grebner S. , Schwarz R. , Vassilev L. , Sieber I. , Schmidt M. , Fuhs W. 
Published: April 2011

ABSTRACTRecently, we have proposed a cyclic method, referred to as Closed Chamber CVD (CC-CVD), for the preparation of μc-Si films of high crystalline fraction at increased deposition rates. In this work we first report new process conditions of CC-CVD, which result in growth of highly crystalline films with a sharp interface on a foreign substrate. Then these conditions are further used together with a pulsed injection of B2H6 in an appropriate moment of each cycle, so that the disturbance of the crystallization process is prevented. A series of ultrathin μc-Si films, doped by this technique, is characterized by conductivity measurements, SEM, Raman Scattering, optical transmission and UV reflection. A strong reduction of the transient interface layer is achieved and conductivity as high as 2 S/cm <p-type> with an activation energy of 27 meV is reached.
A Chemical Bonding Model for Photo-Induced Defects in Hydrogenated Amorphous Silicon (a-Si:H): Intrinsic and Extrinsic Reaction Pathways
Authors: Lucovsky G. , Yang H. 
Published: April 2011

ABSTRACTIn device grade a-Si:H photo- or light-induced defect generation is an intrinsic effect for impurity concentrations of oxygen and nitrogen below about 1019 to 1020 cm−3; however, at higher concentrations it increases with increasing impurity content. Charged defect configurations are identified by empirical chemistry and are studied by ab initio calculations. This paper addresses: i) the chemical stability of charged defects, ii) the reaction pathways for defect metastability, and iii) the transition between extrinsic and intrinsic behavior.
Control of Enhanced Optical Absorption in μc-Si
Authors: Kaan Kalkan A. , Fonash Stephen J. 
Published: April 2011

ABSTRACTThe influence of grain size on the enhanced optical absorption of μc-Si has been investigated using films of various grain sizes prepared by solid phase crystallization. We show that we can control this grain size and therefore the degree of absorption changes. For grain sizes below a threshold range significant absorption enhancement can be seen in the photon energy range of 1 to ∼3 eV and the absorption characteristics of these films show that the dominant mode of optical transitions is indirect. A correlation between first order Raman peak broadening and enhanced absorption was found suggesting both effects are related to confinement. A simple model was developed to see how confinement in the crystallites could influence indirect optical transitions.
Deposition and Characterization of Polycrystalline Silicon Films on Glass for thin Film Solar Cells
Authors: Bergmann R. B. , Krinke J. , Strunk H. P. , Werner J. H. 
Published: April 2011

ABSTRACTWe deposit phosphorus-doped, amorphous Si by low pressure chemical vapor deposition and subsequently crystallize the films by furnace annealing at a temperature of 600°C. Optical in-situ monitoring allows one to control the crystallization process. Phosphorus doping leads to faster crystallization and a grain size enhancement with a maximum grain size of 15 μm. Using transmission electron microscopy we find a log-normal grain size distribution in our films. We demonstrate that this distribution not only arises from solid phase crystallization of amorphous Si but also from other crystallization processes based on random nucleation and growth. The log-normal grain size distribution seems to be a general feature of polycrystalline semiconductors.
Diffusion and Effusion of Hydrogen in Microcrystalline Silicon
Authors: Beyer W. , Hapke P. , Zastrow U. 
Published: April 2011

ABSTRACTThe diffusion and effusion of hydrogen in hydrogenated microcrystalline silicon films deposited in an electron cyclotron resonance reactor were studied for various deposition temperatures Ts. For deposition temperatures below 250°C, hydrogen effusion is found to be dominated by desorption of hydrogen from internal surfaces followed by rapid out-diffusion of H2. Higher substrate temperatures result in an increased hydrogen stability suggesting the growth of a more compact material. For this latter type of samples, a hydrogen diffusion coefficient similar as in compact plasma-grown a-Si:H films is found despite a different predominant bonding of hydrogen according to infrared absorption.
Electrical and Optical Properties of Nano-Crystalline GaN and Nano-Crystalline GaN:H thin Films
Authors: Kobayashi S. , Nonomura S. , Abe K. , Gotoh T. , Hirata S. , Nitta S. , Kanemitsu Y. 
Published: April 2011

ABSTRACTNano-crystalline GaN (nc-GaN) and hydrogenated nc-GaN (nc-GaN:H) thin films and thin film transistors (TFT) prepared by a reactive sputtering method have been studied. Hydrogen incorporation in nc-GaN film induces localized states at mid-gap energy. Thermal annealing at 400 °C and 600 °C creates mid-gap states which is detectable by electron spin resonance. Further thermal annealing treatment at 800 °C reduces the deep states in nc-GaN and nc-GaN:H. Photoluminescence spectra of the nc-GaN film have two broad peaks at 2.4 eV and 3.2 eV. The source-drain current voltage characteristics of the nc-GaN TFT is demonstrated for the first time. The obtained field effect mobility is 10−4 cm2/V-s. Thermal annealing at 800 °C improves the field effect mobility to 10−2 cm2/V-s.
Recrystallization of Amorphous Silicon Deposited on Ultra Thin Microcrystalline Silicon Layers
Authors: Wang F. , Wolfe D. , Lucovsky G. 
Published: April 2011

ABSTRACTThis study reports on a method to reduce the thermal crystallization time and temperature of amorphous silicon films by initially depositing an ultra thin μc-Si:H seed layer. After rapid thermal annealing (RTA), films were characterized by means of Raman spectroscopy, x-ray diffraction, reflection high energy electron diffraction, atomic force microscopy, and dark and photocurrent. The results show that the microcrystalline particles in the seed layer act as nucleation centers, promoting crystallization of a-Si:H at lower temperatures and at shorter times, compared to a-Si:H films deposited without any seed layer. Additionally, it was found that the seed layer affects the orientation of the crystallized films. The dark current increases abruptly over 4 orders of magnitude in the first 15 second anneal, then decreases as the time increases, and tends to saturate. The photocurrent has an opposite behavior. These transport results can be understood in terms of a change in defect density and band gap shrinkage.
High Rate Deposition of a-SiNxH by VHF PECVD
Authors: Takagi T. , Nakagawa Y. , Watabe Y. , Takechi K. , Nishida S. 
Published: April 2011

ABSTRACTVery High Frequency (VHF) has been applied to the plasma enhanced chemical vapour deposition (PECVD) of hydrogenated amorphous silicon nitride films (a-SiNx:H) to fabricate amorphous silicon (a-Si:H) thin film transistors (TFTs). Especially, the effect of the excitation frequency on the deposition rate and the film quality of a-SiNx.H deposited in a SiH4/NH3/N2 plasma has been investigated. The films were prepared by VHF (40 MHz and 60 MHz) and HF (13.56 MHz) plasma enhanced CVD.The optical bandgap, the hydrogen content, the Si-H/N-H ratio and TFT mobility for films deposited in VHF plasma did not change significantly with the increase in deposition rate up to 300 nm/min. Internal stress could be constrained to acceptable levels at very high deposition rates. In contrast, the film quality deteriorated with an increase of the deposition rate in HF plasma. There seems to be a parallel relation between the optical emission intensity and the deposition rate which depends on the excitation frequency.
The Significance of Charged Defects in Understanding the Light-Induced Degradation of Hydrogenated Amorphous Silicon-Germanium Alloys
Authors: Chen Chih-Chiang , Zhong Fan , David Cohen J. 
Published: April 2011

ABSTRACTWe have characterized the defect state structure in a series of device quality glow discharge intrinsic, n-type doped, and p-type doped a-Si,Ge:H alloys with Ge content ranging from 20 at.% to 35 at.%. Our experimental methods include capacitance profiling, transient junction photocurrent and photocapacitance measurements. These methods have allowed us to identify one type of thermally induced defect transition plus two types of optical transitions from deep defects. Our results indicate that these transitions must involve at least two distinct defect sub-bands. Comparison of the magnitudes of these sub-bandsfor the intrinsic, n-type, and p-type alloys has allowed us to confirm that one of the optical transition belongs to D+ defect sub-band. All the optically and thermally induced bands of defect transitions are present with similar magnitudes for the most intrinsic a-Si,Ge:H alloys, which implies that charged defects play a significant role in glow discharge a-Si,Ge:H alloys. We then examined the changes in these defect densities, along with the changes in the hole mobility-lifetime products, that result from prolonged light exposure. By comparing the annealed state and light soaked state of each sample, we have been able to correlate the relative changes of the identified defect sub-band with the measured hole mobility-lifetime products. These data indicate that charged defects probably play a dominant role in determining the degradation of these a-Si,Ge:H alloys in device applications.
Ion Bombardment in Silane VHF Deposition Plasmas
Authors: Hamers E. A. G. , Bezemer J. , Meiling H. , Van Sark W.G.J.H.M. , Van Der Weg W. F. 
Published: April 2011

ABSTRACTThe measurement of mass resolved ion energy distributions at the grounded substrate in an RF glow discharge allows to determine the ion flux and the ion energy flux towards the surface of a growing hydrogenated amorphous silicon (a-Si:H) layer. This provides the means to study the influence of ions on the structural properties of a-Si:H. Here we focus on the α-γ’ transition as occurs in silane-hydrogen plasmas at an RF frequency of 50 MHz and a substrate temperature of 250 °C. The structural properties of the layers appear to depend on the kinetic energy of the arriving ions. This is supported by measurements of ion fluxes under other deposition conditions and by characterization of the corresponding layers. The influence of ions on the growth is discussed in terms of their flux, and the amount of delivered kinetic and potential energy to the growing film. The measurements suggest that a threshold energy of about 5 eV per deposited atom is needed for the construction of a dense amorphous silicon network.
Hydrogen Incorporation During Deposition of a-Si:H From an Intense Source of SiH3
Authors: Van De Sanden M. C. M. , Severens R. J. , Kessels W. M. M. , Van De Pas F. , Van Ijzendoorn L. , Schram D. C. 
Published: April 2011

ABSTRACTThe incorporation of hydrogen during the fast deposition of a-Si:H from an expanding thermal arc is investigated by means of isotope labeling of the precursor gases silane and hydrogen. It is found that hydrogen in a-Si.H originates dominantly from the silyl radical. A small fraction of the hydrogen in a-Si:H is due to exchange reaction of atomic hydrogen in the plasma with hydrogen chemisorbed on the surface during growth.
Observation of Improved Structural Ordering in Low H Content, Hot wire Deposited a-Si:H
Authors: Mahan A. H. , Williamson D. L. , Furtak T. E. 
Published: April 2011

ABSTRACTWe present the results of X-ray diffraction measurements on a series of device quality hot wire (HW) deposited a-Si:H films in which we vary only the substrate temperature of the growing film, which decreases the bonded film H content in a systematic fashion. By increasing the substrate temperature to ∼375°C, where we deposit our low H content (CH) HW films which exhibit a reduced Staebler-Wronski effect, the width of the first peak in the X-ray diffraction pattern narrows noticeably. We interpret this narrowing to be the first indication of improved medium range ordering in our low CH, device quality HW a-Si:H. We note in addition that measurements of the bond angle deviation, obtained from Raman measurements of the half width of the Si-Si TO phonon mode on the same samples, do not show this same evidence of improved ordering as the substrate temperature is increased. We discuss these differences in the context of sample annealing experiments designed to effuse H from the region of the sample probed by the surface sensitive Raman technique, while leaving the bulk of the material, which is sampled by the X-ray beam, largely unaffected.
An Amorphous Silicon Alloy Triple-Junction Solar Cell with 14.6% Initial and 13.0% Stable Efficiencies
Authors: Yang J. , Banerjee A. , Guha S. 
Published: April 2011

ABSTRACTAn initial conversion efficiency of 14.6% has been achieved using amorphous silicon-based alloy in a spectrum splitting triple-junction structure. After 1000 hours of indoor one-sun light soaking at 50 °C, the stabilized efficiency is 13.0%. Both efficiencies are the highest reported to date for amorphous silicon alloy solar cells and have been independently confirmed by the National Renewable Energy Laboratory. The device was deposited onto a stainless steel substrate coated with textured silver/zinc oxide back reflector. The bottom and middle cells use amorphous silicon-germanium alloys, employing high hydrogen dilution in the gas mixture and bandgap profiling in the cell design. The top cell uses amorphous silicon alloy with high hydrogen dilution. Key factors leading to the achievement include a) improvement of the bottom cell that exhibits an AM1.5 efficiency of 10.4% and quantum efficiency of 45% at 850 nm; b) improvement of the tunnel junctions between the component cells by incorporating a novel multilayered structure with microcrystalline p and n layers; and c) improvement of transparent conductive oxide for enhancing the short wavelength response of the top cell.
Persistent Photoconductivity, the Staebler-Wronski Effect, and Long-Range Disorder in a-Si:H
Authors: Quicker D. , West P. W. , Kakalios J. 
Published: April 2011

ABSTRACTWe report measurements of the conductivity, thermopower, and conductance fluctuations before and after light exposure for a-Si:H samples that show either persistent photoconductivity (PPC) or a Staebler-Wronski effect. Both the conductivity and thermopower are changed by light exposure, but no change is observed in the difference between the conductivity and thermopower activation energies for any of the samples studied here. This suggests that the long-range disorder is unaffected by light exposure. For some samples, the magnitude or statistical properties of the conductance fluctuations are affected by light exposure. We compare these results to previous studies of the Staebler-Wronski effect and discuss their implications for models of the light-induced changes and the 1/f noise in a-Si:H.
More Insights into Band Gap Graded a-SiGe:H Solar Cells by Experimental and Simulated Data
Authors: Zimmer J. , Stiebig H. , Fölsch J. , Finger F. , Eickhoff Th. , Wagner H. 
Published: April 2011

ABSTRACTAn experimental and numerical study of a-SiGe:H based solar cells with band gap graded i-layer in the shape of a ‘V’ is presented. The variation of the location of the band gap minimum has strong influence on the solar cell performance. Comparisons of experimental and simulated data of the dark IV-behavior, IV-curves under illumination and the quantum efficiency allow insights into the transport and recombination behavior within the solar cell. The simulations reveal that the position as well as the charge state of the defects determine the device characteristics.
The Effects of Hydrogen Dilution on VOC in a-Si:H Pin Solar Cells
Authors: Wang Qi , Crandall Richard S. , Han Daxing 
Published: April 2011

ABSTRACTWe study the effects of hydrogen dilution on the open circuit voltage of a-Si:H pin solar cells fabricated by rf glow discharge growth. We keep the p and n layers the same and only vary the i layer properties. A normal a-Si:H i layer, an H-diluted i layer, and a thin H-diluted layer inserted between p and normal i layer are selected for this study. We measure the JV characteristics and the internal electric field distribution using a transient-null-current technique both in annealed and light soaked states. We find that hydrogen dilution does stabilize the Voc either in a bulk H-diluted i layer or in a thin layer between p and normal i layer after 100 hours AMI sun light soaking. From dark IV measurement, both H-diluted cells show little change in current at voltage near Voc before and after light soaking; while the normal a-Si:H cell does show a noticeable change. Also the internal field measurements find a stronger electric field starting from p and i interface for both H-diluted cells compared to the normal a-Si:H cell. Furthermore, there are no measurable changes in the field profiles after 100 hour AMI light-soaking for both H-diluted and normal a-Si cells. All these suggest that hydrogen dilution increases the field strength near p and i interface, which is the key that leads to a more stable Voc of H-diluted cells.
Photogeneration and Carrier Transport in Amorphous Silicon/Crystalline Silicon Devices
Authors: Jagannathan B. , Anderson W. A. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon (a-Si:H)/ crystalline silicon (c-Si) type heterodiodes in solar cell structures have been studied by rf glow discharge, dc magnetron sputtering, and a remote plasma deposition of a-Si:H onto p type c-Si. Carrier transport and photogeneration in such structures have been investigated by current-voltage-temperature, thermally stimulated capacitance (TSCAP), and spectral response experiments. Dark carrier conduction is found to be a combination of tunneling and interface recombination, but is dominated by either one depending on the deposition/sputtering conditions. The conditions investigated include energy of the plasma species, type of plasma cleaning, and substrate preparation techniques. For each of the conditions, the trap type, energy and concentration have been identified by TSCAP. Solar cells fabricated by the optimized fabrication scheme routinely yield 10.5% efficient devices having a short circuit current density (Jsc) of 30 mA/cm2, a open circuit voltage of 0.55 volts and a fill factor (FF) of 0.64, without an AR coating, over 0.3 cm2 area.
Amorphous-Silicon Thin-Film Transistors Matched to Ultra-Large Panels
Authors: Matsumura Masakiyo , Saitoh Akihiko 
Published: April 2011

ABSTRACTTime-delay problems will become extremely severe in active-matrix-addressed ultra-large liquid-crystal display-panels. The problem caused by large crossover capacitance can be solved by moving the signal bus-line to the facing glass plate. The problem caused by large gate capacitance can be solved only by reducing the TFT channel much shorter than the conventional value. This requirement can be satisfied by a novel vertical TFT fabricated by using a selective excimer-laser crystallization method. Switching characteristics have been evaluated for the prototype devices, and good on-characteristics have been confirmed for the O.5μm-long gate device. Improved device structures are also presented.
Amorphous Silicon Photodiode-Thin Film Transistor Image Sensor with Diode on Top Structure
Authors: Powell M J , Glasse C , French I D , Franklin A R , Hughes J R , Curran J E 
Published: April 2011

ABSTRACTWe have developed a new amorphous silicon image sensor technology using a matrix array of amorphous silicon thin film transistors and photodiodes, where the amorphous silicon nip photodiode is fabricated on top of a thick insulating layer, on top of the thin film transistor array. We call this ‘diode on top’ technology or DOTTY. The active diode area can be as high as 93%, compared to 50% for our conventional photodiode-TFT technology. This leads to a higher signal to noise performance, which is important for medical X-ray applications.
Charge Collection I.N A Se Photoconductor on a Thin Film Transistor Array during X-Ray Imaging
Authors: Brauers A. , Conrads N. , Frings G. , Schffibel U. , Powell M. J. , Glasse C. 
Published: April 2011

ABSTRACTThis paper deals with performance aspects of a selenium photoconductor on a thin film transistor array when used in x-ray imaging, e.g. for medical applications. We present the effects of doping structures within the Se on the spatial resolution, temporal response and dark current characteristics. Measurements were done on a 1922 pixel array with 200 μm pitch and a collecting electrode covering 50 % of the pixel area. Without additional measures the detector has a prohibitively slow response. With properly chosen doping structures the lateral conductivity can be engineered in a manner that the speed of the Se-TFT detector is increased to a level acceptable for video rate imaging. There is also a critical relationship between doping structures in the photoconductor and the spatial resolution of the detector. An idea of how these doping structures work in terms of resolution and speed of the detector is presented, together with proposals for an optimized doping scheme.
Improved Concept for Nipiin and PIIIN Color Sensitive Two-Terminal Devices with High Linearity
Authors: Knipp D. , Stiebig H. , Fölsch J. , Carius R. , Wagner H. 
Published: April 2011

ABSTRACTThe detection of the fundamental components of the visible light (blue, green, red) is achieved with two terminal photo diodes based on amorphous silicon. By changing the bias voltage the preferential carrier collection region is shifted which leads to a color sensitivity. In order to obtain a high dynamic range, independent voltage controlled spectral response curves as well as a linear response of the photocurrent on the incident light intensity the μτ-product and the bandgap in the device have to be specially designed to deconvolute the optical signal and generate an RGB-signal. Since the light intensity can strongly influence the spectral sensitivity by recharging of defect states, an optimized design of the multi-layer structure is necessary. Therefore, an improved concept for the design of nipiin- and piiin-detectors is presented which results in a good suppression of these non-linearities. Our concept is based on a decreasing bandgap profile from the front to the back contact and an increasing μτ-product of the individual i-layers in direction of the p-layer.
Rugged Thin Film Diode Liquid Crystal Switches Based on Amorphous Sinx:H
Authors: Mc Garvey B , Clegg J B , Deane S C , Sandoe J N , Shannon J M 
Published: April 2011

ABSTRACTAmorphous SiNx:H thin film diodes (TFDs) can be used for pixel addressing in active matrix liquid crystal displays. They depend on the application of high electric fields to switch from the ‘off to the ‘on’ states. They prove to be remarkably rugged and can be made with high yield and tolerance. An important feature that contributes to this ruggedness is the ability of these switches to generate defect states at a rate dependent on current density. Current induced defect states trap electrons and cause a reduction in field at the cathode contact, which in turn causes a reduction in current density. Therefore, current will be transferred from regions of high current to regions of low current in the device, making the current flow more uniform. TFDs with thin regions will become effectively thicker during current stressing. In order to check this hypothesis, thin film diodes with nonuniform thickness a-SiNx:H layers were current stressed, and the I-V characteristics compared with those calculated using a defect generation model. The experimental data agreed well with our theoretical model.