bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real-time spectroscopic ellipsometry as an in-situ probe of the growth dynamics of amorphous and epitaxial crystal silicon for photovoltaic applications
Authors: Levi D.H. , Teplin C.W. , Iwaniczko E. , Yan Y. , Wang T.H. , Branz H.M. 
Published: June 2019

AbstractIn this paper we report on our work using in-situ real time spectroscopic ellipsometry (RTSE) to study the dynamics of hot-wire chemical vapor deposition (HWCVD) of hydrogenated amorphous silicon (a-Si:H) and epitaxial crystal silicon (epi-Si) for photovoltaic applications. We utilize RTSE as both an in-situ diagnostic and a postgrowth analysis tool for a-Si:H/crystalline silicon heterojunction (SHJ) solar cells and epi-silicon films grown by HWCVD. RTSE enables precise thickness control of the 3 to 10 nm thick layers used in the SHJ devices, as well as monitoring crystallinity and surface roughness in real time. With the assistance of in-situ RTSE feedback we have achieved a photovoltaic energy conversion efficiency of 17% on an Al-backed p-type float-zone c-Si wafer. Open-circuit voltages above 650 mV indicate excellent passivation of the c-Si surface by the a-Si:H intrinsic layer. We have used RTSE to obtain information on the degree of crystallinity and the electronic and optical properties of films as a function of deposition conditions. RTSE has indirectly indicated the persistence of a hydrogen layer at the interface between the a-Si:H layer and the crystal silicon substrate. Absorption spectra determined by RTSE have provided guidance in device optimization.We are also applying in-situ RTSE to study the dynamics of HWCVD growth of epi-Si. The goal of this work is to develop low-temperature methods for growing 2-10 μmthick layers of c-Si on c-Si seed layers on glass for solar cell applications. This study presents unique challenges for RTSE, as perfect epitaxial growth of c-Si on a c-Si wafer would produce no change at all in the RTSE spectra. We have found that by monitoring the pseudo-dielectric function in real time during growth we gain immediate feedback on the breakdown of epi-Si growth. Post-deposition analysis of the RTSE data provides quantitative information on the percent of c-Si and a-Si versus film thickness. The RTSE analysis has been confirmed by cross sectional TEM. Based on the rapid feedback provided by RTSE we have surpassed the previous HWCVD maxiumum of 200 nm of epi-Si growth, achieving a maximum thickness of 500 nm of epi-Si. TEM analysis has shown that micron-sized areas of these films achieve 1000 nm of epi-Si thickness.
Development of Deposition Phase Diagrams for Thin Film Si:H and Si1-xGex:H Using Real Time Spectroscopic Ellipsometry
Authors: Podraza N. J. , Ferreira G. M. , Wronski C. R. , Collins R. W. 
Published: June 2019

AbstractThe growth of hydrogenated silicon (Si:H) and silicon-germanium alloys (Si1-xGex:H) by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) substrates has been studied by real time spectroscopic ellipsometry (RTSE). The motivation is to develop deposition phase diagrams that can provide greater insight into the optimization of amorphous Si1-xGex:H (a-Si1-xGex:H) for multijunction photovoltaics. In initial studies, the phase diagram for bottom cell a-Si1-xGex:H (Eg ˜ 1.4 eV) is found to exhibit fundamental similarities to that for Si:H when both materials are prepared under standard PECVD conditions that optimize pure a-Si:H. These similarities suggest directions for optimizing a-Si1-xGex:H by identifying conditions under which a smooth, stable surface is obtained to the largest possible bulk layer thickness. In phase diagram development for PECVD Si1-xGex:H on c-Si, it has been found that the highest surface stability and smoothest surfaces are obtained using cathodic deposition (self bias: ˜-20 V) with a H2-dilution level just below that of the amorphous-to-(mixed-phase microcrystalline) [→(a+μc)] transition for a thick layer. Due to the promising nature of these results, full phase diagrams are compared for cathodic and anodic Si1-xGex:H as well as for cathodic and anodic Si:H, all on c-Si substrates. The cathodic phase diagram for Si1-xGex:H reveals a narrow range of significant improvement in surface structural evolution near the →(a+μc) transition, and for a-Si:H reveals an extension of the ultrasmooth protocrystalline regime to a much wider range of thickness.
Threshold Voltage Optimization with Ion Shower Implantation for Polysilicon Thin-film Transistors
Authors: Choi B. D. , Choi D. C. , Im C. Y. , Choi K. H. , Yu C. H. , Kakkad R. , Chung H. K. 
Published: June 2019

AbstractIn this paper, we present the results of ion shower implantation to adjust threshold voltages on ELC (excimer laser crystallized) poly silicon thin film transistors. We observed that the threshold voltages of poly Si TFT strongly depended on the shower implantation dose, not the shower implantation energy for the 500 Å-thick active silicon layer. The threshold voltages for the reference, dose 5×1011 cm-2, and 1×1012 cm-2 cases were 0.30V, 1.25V, and 2.04V, respectively. We conclude that the threshold voltage can be appropriately adjusted by tuning the dose of the counter doping shower implant and its DIBL can still be suppressed to within an acceptable level.
PECVD grown hydrogenated polymorphous silicon studied using current transient spectroscopies in PIN Diodes
Authors: Tripathi Vibha , Mohapatra Y. N. , Roca i Cabarrocas P. 
Published: June 2019

AbstractHydrogenated polymorphous silicon (pm-Si:H) has steadily emerged as a potential replacement of hydrogenated amorphous silicon. Possible changes in the density of gap states due to the presence of crystallites is of central importance in understanding steady state and dynamic characteristics of devices using these materials. We have studied a-Si:H and pm-Si:H grown by PECVD at optimized conditions through the measurement of the steady state reverse current and their transients in PIN devices. The transients are analyzed using isothermal spectroscopic techniques such as Time Analyzed Transient Spectroscopy (TATS), and high resolution Laplace DLTS as a function of temperature. In case of a-Si:H, we obtain the expected signature of emission from a broad density of states in the form of stretched exponentials. In contrast the corresponding spectra for pm-Si:H are dominated by nearly exponential fast current decay processes with discrete energies between 0.20 and 0.26 eV. It is shown that the study of the density of states by dynamic methods such as transient techniques reveal features not accessible to steady state measurements.
Ge Growth on Nanostructured Silicon Surfaces
Authors: Vanamu Ganesh , Datye Abhaya K. , Zaidi Saleem H. 
Published: June 2019

AbstractWe report highest quality Ge epilayers on nanoscale patterned Si structures. 100% Ge films of 10 μm are deposited using chemical vapor deposition. The quality of Ge layers was examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD) measurements. The defect density was evaluated using etch pit density measurements. We have obtained lowest dislocation density (5×105 cm-2) Ge films on the nanopatterned Si structures. The full width half maximum peaks of the reciprocal space maps of Ge epilayers on the nanopatterned Si showed 93 arc sec. We were able to get rid of the crosshatch pattern on the Ge surface grown on the nanopatterned Si. We also showed that there is a significant improvement of the quality of the Ge epilayers in the nanopatterned Si compared to an unpatterned Si. We observed nearly three-order magnitude decrease in the dislocation density in the patterned compared to the unpatterned structures. The Ge epilayer in the patterned Si has a dislocation density of 5×105 cm-2 as compared to 6×108 cm-2 for unpatterned Si.
Polycrystalline GeC Thin Films Deposited Using a Unique Hollow Cathode Sputtering Technique
Authors: Soukup R. J. , Ianno N. J. , Schrader J. S. , Dalal V. L. 
Published: June 2019

AbstractExperimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented. The mostimportant contribution of this work is that it shows that by using non-equilibrium growth conditions resulting from the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. The sputtering is accomplished by igniting a dc plasma in the Ar and H2 gases which are fed through Ge and C nozzles.The GeC films are grown on etched Si (100), on Si with the native oxide and on glass. The films grown on glass were quite disordered, but the films grown on both types of Si substrates were very ordered in nature. This order has been characterized using Xray diffraction (XRD) and Raman spectroscopy.Films with as much as 8% C have been deposited. In order to produce useful GexC1-x films, the C must bond to the Ge at lattice sites. Evidence of this desired GeC bond has been seen using Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and XRD.
Characterization of the Silicon-Based Thin Film Multi-Junction Solar Cells
Authors: Hishikawa Yoshihiro 
Published: June 2019

AbstractTechnical issues for the performance characterization of silicon-based thin-film multi-junction devices, such as the a-Si/thin-film c-Si structure, are discussed. The measured spectral response of each component cell is affected by the shape of the I-V curves of the component cells under color bias light, as well as the applied bias voltage. This paper describes procedures for correcting the measured spectral response. High-fidelity solar simulators, which incorporate Xe lamp(s) and halogen lamps that simulate AM1.5G standard sunlight, are very useful for characterizing the I-V curves of the multi-junction devices. They can accurately reproduce the current generated in each component cell and the I-V curve of the devices under standard sunlight, with a simple spectral adjustment procedure, thanks to their basic good spectral fidelity to standard sunlight. The irradiance dependence of the I-V curve is important for translating the I-V curve under different irradiance conditions. Although translation is not straightforward for multi-junction devices, the experimental results of the present study suggest that it is possible under spectral conditions where the relative value of the photocurrent among the component cells is constant. Determination of the I-V curve of each component cell based on the I-V curves of the multi-junction devices is also mentioned.
Structure of microcrystalline solar cell materials: What can we learn from electron microscopy?
Authors: Luysberg M. , Houben L. 
Published: June 2019

AbstractMicrocrystalline silicon and its group IV alloys are widely explored as absorber layers in thin film solar cells. Despite the extended research in recent years the fundamental understanding of the relation between macroscopical properties, i.e. electrical and optical properties, and the microstructure is poor. Clearly, the structure of microcrystalline materials, consisting of a phase mixture between “amorphous” material, crystalline grains, and voids, is complex. To demonstrate the strengths and limitations of transmission electron microscopy on microcrystalline materials, we will discuss different techniques employed to investigate grain sizes and morphologies, crystallographic orientations, amorphous volume fractions, and lateral arrangements of crystallites. In particular, we focus on the potential for analyzing the structure of grain boundaries and the amorphous phase in microcrystalline silicon and silicon carbide by the most advanced techniques in atomic resolution imaging in the transmission electron microscope.
Microcrystalline and Nanocrystalline Silicon: Simulation of Material Properties
Authors: Biswas R. , Pan B. C. , Selvaraj V. 
Published: June 2019

AbstractWe have simulated nano-crystalline silicon and microcrystalline silicon structures with varying crystallite volume fractions, using molecular dynamics simulations. The crystallite regions reside in an amorphous matrix. We find the amorphous matrix is better ordered in nanocrystalline-Si than in the homogenous amorphous silicon networks, consistent with the observed higher stability of H-diluted films. There is a critical size above which the crystallites are stable and may grow. Sub-nm size crystallites in the protocrystalline phase are found to reduce the strain of the amorphous matrix. We simulated micro-crystalline silicon with a substantial crystallite volume fraction. Microcrystalline structures exhibit a crystalline core surrounded by an amorphous shell with similarities to silicon nanowires. We find a relatively uniform H distribution in the amorphous region and a crystal-amorphous phase boundary that is not welldefined.
Effects of Post Annealing and Material Stability on Undoped and n+ nc-Si:H Films Deposited at 75 °C Using 13.56 MHz PECVD
Authors: Lee Czang-Ho , Sazonov Andrei , Nathan Arokia 
Published: June 2019

AbstractThe effects of post-deposition annealing and material stability of undoped and n+ nanocrystalline silicon (nc-Si:H) films deposited at 75 °C using standard 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) have been investigated. Electrical, structural, and chemical composition properties of the films at ambient atmosphere were studied before and after the thermal annealing. The dark conductivity (σd) in all films demonstrated high stability against prolonged ambient atmosphere exposure, which can be attributed to stable hydrogen passivation of the grain boundaries. On the other hand, in undoped nc-Si:H films, the σd increases by more than one order of magnitude after annealing in ambient atmosphere, followed by a decrease below the as-grown value. Depending on the annealing temperature, the σd can drop as low as 10-8 S/cm. In n+ nc-Si:H films, the decrease in the σd was lower. However, in undoped nc-Si:H films capped by an amorphous silicon nitride (a-SiN:H), this was not observed. In all films, no significant change in the film microstructure before and after annealing was detected. However, a small decrease in the hydrogen content (CH) accompanied by an increase in the oxygen content (CO) was observed in uncapped undoped nc-Si:H films. It was therefore concluded that the σd is affected by oxygen desorption due to annealing and its absorption from the ambient atmosphere. Based on experimental results, we propose a possible model in terms of hydrogen effusion-assisted oxygen absorption.
Characterization of Silicon thin Film Deposited by E-Beam Evaporator for Flexible Display
Authors: Song In-Hyuk , Han Sang-Myeon , Park Jung-Hyun , Han Min-Koo 
Published: June 2019

AbstractThe structure and crystal growth of the silicon thin film deposited by e-beam evaporator have been studied with use of scanning electron microscopy (SEM), x-ray diffraction and transmission electron microscopy (TEM). The silicon thin film is deposited at room temperature for flexible display. It is found that the silicon film deposited by e-beam evaporator has polysilicon structure by scanning electron microscopy (SEM). SEM image also shows that grain size of the silicon film is about 50nm. X-ray diffraction of the silicon thin film represents that the orientation of the silicon film is (201). We have also investigated the structure and the crystal growth of the silicon film after the silicon film is irradiated by XeCl excimer laser with various energy densities. Transmission electron microscopy shows that the irradiated silicon thin film has low intra-grain defects and sharp grain boundary.
Electron Field Emission from SiC/Si Heterostructures Formed by Carbon Implantation into Silicon and Etching of the Top Silicon Layer
Authors: Xing Yumei , Zhang Jihua , Yu Yuehui , Song Zhaorui , Shen Dashen 
Published: June 2019

AbstractHigh intensity electron field emissions were obtained from SiC/Si heterostructures formed by high temperature carbon implantation into silicon and subsequently etching of the top silicon layer. Implantation processes were performed at 700 °C with a dose of 3.0 to 8.0 x 1017 ions/cm2. Post-implantation annealing in argon at 1250 °C for 5h was done for partial samples. β-SiC precipitates were easily formed and embedded in silicon at the interface of SiC/Si heterostructures during high temperature carbon implantation for all samples. The densely distributed small protrusions led to efficient electron emission. Implantation dose scarcely impacted the electron emission characteristics when it reached to a definite value. After annealing, the density of protrusions at the interface of SiC/Si heterostructures became smaller since β-SiC precipitates were grown into larger sizes, which caused to a relatively inefficient electron emission.
Excimer Laser Crystallized HWCVD Thin Silicon Films: Electron Field Emission
Authors: Shaikh M. Z. , O'Neill K. A. , Persheyev S. K. , Rose M. J. 
Published: June 2019

AbstractThin silicon films deposited using the Hot-Wire Chemical Vapor Deposition (HWCVD) technique are studied here for the effect of XeCl excimer laser crystallization on their structural, optoelectronic, and electron field emission properties. Excimer Laser Annealing (ELA) of the silicon thin films indicated increased dark conductivity and reduced optical gap. Encouraging Field Emission (FE) results were obtained from XeCl excimer laser processed HWCVD films on Cr, V, Mo, and Ti backplanes. Geometric field enhancement factors from surface measurements and Fowler-Nordheim Theory (FNT) were compared. FE thresholds were also found to be particularly influenced by the backplane material.
GaAs Growth on Micro and Nano Patterned Ge/Si1-XGeX and Si Surfaces
Authors: Vanamu Ganesh , Datye Abhaya K. , Dawson Ralph L. , Zaidi Saleem H. 
Published: June 2019

AbstractWe show heteroepitaxial growth of GaAs on Ge/SiGe grown on nanometer-scale grating structures. Conventional lithography techniques were combined with reactive ion and wet-chemical etching to fabricate 1-D patterns of silicon posts. The quality of the GaAs layers was investigated using high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) and etch pit density (EPD) measurements. Our results show significant improvement in the quality of heteroepitaxial layers grown on nano patterned structures compared to those on the unpatterned silicon. The optical quality of the GaAs/Ge/SiGe on nano-scale patterned silicon was comparable to that of single crystal GaAs.
High-Temperature Nanoindentation Measurement for Hardness and Modulus Evaluation of Low-k Films
Authors: Ye Jiping , Kojima Nobuo , Shimizu Satoshi , Burkstrand James M. 
Published: June 2019

AbstractA high-temperature nanoindentation measurement method has been developed for evaluating the hardness and modulus of low-k films when the temperature is raised from R.T. to 200°C. Thermal stability and chemical changes due to heating were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis, and by thermal desorption spectroscopy, respectively. Two different classes of low-k materials, organic polyarylence ether film and methyl-hydrogen-silsesquioxane film, were examined. The hardness and modulus of the former film during heating increased due to water desorption in the lower temperature range, and then decreased due to the evolution of hydrocarbon gas from some unreacted components or solvent residuals in the higher temperature range. In regard to the latter film, the hardness and modulus of a specimen (A) having a higher hydrocarbon content decreased during heating and reached the lowest value at 200°C and then constantly remained at the lowest levels during cooling. In contrast, no significant changes in hardness and modulus were observed for a specimen (B) having a lower hydrocarbon content in either the heating or cooling process. The reduction of the hardness and modulus of specimen A was attributed to thermal decomposition of most of its Si-CH3 and SiH/SiH2 chains. These results revealed that the temperature dependence of the hardness and modulus of low-k films is significantly affected by physical and/or chemical changes during heating due to moisture absorption, thermal evolution of organic residuals and thermal decomposition, rather than other factors such as thermal stress.
Integration of a Polymer Etch Stop Layer in a Porous Low K MLM Structure
Authors: Smith Gregory C. , Henis Neil , McGowan Richard , White Brian , Kraatz Matthias , Satyanarayana Sri , Hosali Sharath , Liu Youfan , Pfeifer Klaus 
Published: June 2019

AbstractTwo level metal structures were fabricated to test the efficacy of using an organic low K etch stop layer (OESL) in order to lower the effective dielectric constant for intralayer capacitance. The organic etch stop layer's intrinsic capacitance of 3.3 compares with that of silicon carbide (∼ 5) which constitutes the control of the experiment. This reduction represents a reduction of effective dielectric constant for the stack of about 10% to about 3.0. The process was optimized so as to achieve yield of via chains of a million 130 nm diameter vias, and effective K was measured. The target of 3.0 was achieved using this process. Interpenetration of the organic etch stop with the MSQ porous low K material was observed.
Nanoscale Observation of Dielectric Damage to Low k MSQ Interconnects from Reactive Ion Etching and Ash Treatment
Authors: Gross Todd S. , Yao Shaoning 
Published: June 2019

AbstractElectrostatic force microscopy (EFM) was used to measure the extent of dielectric damage from plasma processing of nanoporous, low k methyl silsesqioxane (MSQ) interconnect structures with approximately 50 nm spatial resolution. Single level patterns were formed in 200 nm thick MSQ films by reactive ion etching (RIE) and were subsequently backfilled with an MSQ layer that was not exposed to plasma to act as a reference. The backfill was performed on as-etched structures with the photoresist intact and on structures in which the photoresist was removed by an oxygen plasma (ash) treatment. The EFM images on cross sections and feather sections show that the damage from the RIE penetrated ∼100 nm in from the sidewall and that the redeposited polymer had a higher k than the MSQ (k∼2.2). The etched and ashed MSQ exhibits a higher dielectric constant than the reference MSQ if it was exposed to water and has nearly the same dielectric constant as the reference with no water exposure. This suggests that the damage from the ash acts to make the MSQ hydrophilic.
Observation of Intrusion Rates of Hexamethyldisilazane During Supercritical Carbon Dioxide Functionalization of Triethoxyfluorosilane Low-k Films
Authors: Capani P.M. , Matz P.D. , Mueller D.W. , Kim M.J. , Walter E.R. , Rhoad J.T. , Busch E.L. , Reidy R.F. 
Published: June 2019

AbstractWater adsorption by porous low-k silica films results in increased dielectric constants and is often due to silanol groups on the pore surfaces. Reacting the silanols with silylating agents (e.g., hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS)) in supercritical CO2 (SC-CO2) can increase film hydrophobicity and can remove adsorbed water. In porous methylsilsesquioxane (MSQ) films (average pore size ∼ 3-4nm), it has been determined that supercritical silylation reactions do not substantially penetrate beyond the film surface.1,2 In this work we have examined the supercritical penetration behavior of silylating agents in low-k films with larger pore sizes (5-10nm). The depth and extent of reactants was determined by in situ infrared spectroscopy (FTIR), and surface hydrophobicity was examined by contact angle experiments.