bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved interface between front TCO and microcrystalline silicon p-i-n solar cells.
Authors: Vallat-Sauvain E. , Faÿ S. , Dubail S. , Meier J. , Bailat J. , Kroll U. , Shah A. 
Published: April 2011

ABSTRACTThe microstructure of microcrystalline silicon p-layers on zinc oxyde (ZnO) has been studied by Transmission Electron Microscopy (TEM). ZnO has been characterised by X-Rays diffraction and by Scanning Electron Microscopy (SEM). These reveal that the ZnO surface topography consists of regular pyramids with a (110) preferential crystallographic growth axis. High Resolution TEM observations indicate that the p- layer growth starts at the top of the ZnO pyramids. This results, for fully microcrystalline p-layers, in a decreased thickness at the bottom of the ZnO pyramids. When the p-layer is fully microcrystalline, no amorphous incubation layer could be observed between ZnO and p-silicon layer. Moreover, the high crystallinity of the p-layers in microcrystalline p-i-n devices is accompanied by an increased fill-factor in the I-V characteristics.
Microcrystalline Silicon Thin-Film Solar Cells Prepared at Low Temperature
Authors: Nasuno Y. , Kondo M. , Matsuda A. 
Published: April 2011

ABSTRACTHydrogenated microcrystalline silicon (µc-Si:H) p-i-n solar cells have been prepared using a conventional RF plasma-enhanced chemical vapor deposition (PECVD) method at a low process temperature of 140 °C. The low temperature deposition of µc-Si:H has been found to be effective to suppress the formation of oxygen-related donors that cause a reduction in open circuit voltage (Voc) due to shunt leakage. We demonstrate the improvement of Voc by lowering the deposition temperature down to 140, while suppressing the reduction in high short circuit current density (Jsc) and fill factor (FF). A high efficiency of 8.9% was obtained using an Aasahi-U substrate. Furthermore, by optimizing textured structures on ZnO transparent conductive oxide (TCO) substrates, an efficiency of 9.4% (Voc=0.526V, Jsc=25.3mA/cm2, FF=0.710) was obtained. In addition, relatively high efficiency of 8.1% was achieved using VHF (60MHz) plasma at a deposition rate of 12 Å/s. Thus, this low temperature deposition technique for µc-Si:H is promising for both high efficiency and high rate deposition of µc-Si:H solar cells.
Evolution of the Mobility Gap with Thickness in Hydrogen-Diluted Intrinsic Si:H Materials in the Phase Transition Region and Its Effect on p-i-n Solar Cell Characteristics
Authors: Koval R.J. , Pearce J.M. , Ferlauto A.S. , Collins R.W. , Wronski C.R. 
Published: April 2011

ABSTRACTInsights into the growth processes and evolution of microstructure in intrinsic hydrogenated silicon (Si:H) films obtained from real-time spectroscopic ellipsometry (RTSE) are extended to the characterization of the optoelectronic properties of the corresponding solar cells. To assess the effects of transition regions from the amorphous to mixed microcrystalline phases, cell structures with and without such regions at different depths in the i-layer from the p-contact have been investigated. Experimental results are presented that clearly demonstrate changes in the mobility gap, Eµ, of the materials as their microstructure evolves with thickness, further supporting the important effect of the hydrogen dilution ratio R (R[H2]/[SiH4]) on the transition between the amorphous and microcrystalline phases. Light J-V characteristics at room temperature and dark J-V characteristics at different temperatures were measured on p(a-SiC:H:B)-i(Si:H)-n(µc-Si:H:P) solar cell structures with i-layers of different thicknesses and R values. The mobility gaps of both the amorphous and microcrystalline intrinsic-layer materials as well as those of the transition layers are obtained from dark J(V,T) measurements. Using numerical simulation, both the light and the dark J-V characteristics are self-consistently modeled assuming sharp changes in the mobility gaps at the intrinsic layer transition thicknesses determined by RTSE.
Defect Density Profiling in Light-Soaked and Annealed Hydrogenated Amorphous Silicon Solar Cells
Authors: Crandall Richard S. , Yang Jeffrey , Guha Subhendu 
Published: April 2011

ABSTRACTThe fundamental ingredient lacking in solar cell modeling is the spatial distribution of defects. To gain this information, we use drive-level capacitance profiling (DLCP) on hydrogenated amorphous silicon solar cells. We find the following: Near the p-i interface the defect density is high, decreasing rapidly into the interior, reaching low values in the central region of the cell, and rising rapidly again at the n-i interface. The states in the central region are neutral dangling-bond defects whose density agrees with those typically found in similar films. However, those near the interfaces with the doped layers are charged dangling bonds in agreement with the predictions of defect thermodynamics. We correlate the changes in solar cell efficiency owing to intense illumination with changes in the defect density throughout the cell. Defects in the central region of the cell increase to values typically found in companion films. We describe the measurements and interpretation of DLCP for solar cells with the aid of a solar cell simulation.
Photoluminescence Study of Self-Limiting Oxidation in Nanocrystalline Silicon Quantum Dots
Authors: Arai Kenta , Omachi Junichi , Nishiguchi Katsuhiko , Oda Shunri 
Published: April 2011

ABSTRACTWe have studied photoluminescence (PL) of surface oxidized nanocrystalline silicon quantum dots (QDs) for various oxidation periods and temperatures. With increasing oxidation period, the surface oxide grows and the Si QD core shrinks initially, then retardation of the oxidation process occurs which is ascribed to compressive stress at the interface between Si QD core and oxide. Upon oxidation, the PL spectrum peak shifts toward the shorter wavelength side followed by retardation of the blueshift or even manifestation of the redshift. The origin of PL is due to the localized excitons at the interface between Si QD core and oxide or amorphous SiOx (a-SiOx) formed at the interface. The blueshift is associated with the increased quantum con.nement or increased bandgap of a-SiOx. The redshift is due to the stress e.ect of the bandgap of Si QD core or a-SiOx. We have successfully confirmed the effect of compressive stress associated with the self-limiting oxidation by PL measurement.
Carrier transport and photogeneration in large area p-i-n Si/SiC heterojunctions
Authors: Louro P. , Vygranenko Yu. , Schwarz R. , Fernandes M. , Vieira M. , Gloeckner J. , Schubert M. 
Published: April 2011

ABSTRACTGlass/ZnO:Al/p (SixC1−x:H)/i (Si:H)/n (SixC1−x:H)/Al (0<x<1) heterojunction cells were produced by PE-CVD at low temperature. Junction properties, carrier transport and photogeneration are investigated from illuminated current- and capacitance- voltage characteristics and spectral response measurements, in dark and under different illumination conditions. For the heterojunction cells high series resistance around 106 ω and atypical J-V characteristics are observed leading to poor fill factors, also it was observed that the responsivity decreases with the increase of the light bias intensity. For the homojunction the behaviour is typical of a non optimised p-i-n cell and the responsivity varies only slightly with the light bias conditions. A numerical simulation gives insight into the transport mechanism suggesting that in the heterojunctions and in dark conditions the transport mechanism depends almost exclusively on field-aided drift while under illumination it is dependent mainly on the diffusion of free carriers.
Microcrystalline Germanium Carbide: A New, Almost Direct Gap, Thin Film Material for Photovoltaic Energy Conversion
Authors: Dalal Vikram L. , Herrold Jason T. 
Published: April 2011

ABSTRACTWe report on the growth and electrical and optical properties of micro- and poly- crystalline Ge1−x Cxfilms. This is a new material which does not exist in nature. The films were grown using ECR plasma techniques under conditions of low pressure and high power from a mixture of germane, methane and hydrogen. The bandgap of the material could be varied from that of c-Ge (∼0.7 eV) to almost 1.15 eV by changing the methane/germane ratio. X ray diffraction and Raman measurements indicated good crystallinity in the film. The optical absorption spectrum of the film resembles that of c-Ge, with a near direct bandgap, implying that as C is added, both the central and the L valley in the conduction band move up simultaneously, while maintaining a small (∼0.15 eV) separation between the two. The Hall mobility was measured to be 70 cm2/V-sec. The films were doped n- type using phosphine, and p- type using diborane. P-n junctions with good rectification characteristics were fabricated. Because of its excellent optical absorption, this material may be suitable for photovoltaic applications, particularly for tandem junction cells. We have also observed that grain size can be controlled using H etching, and have observed distinct changes in optical properties related to quantum size effects in c-Ge films.
Porous silicon thin film gas sensor
Authors: Ferreira I. , Fortunato E. , Martins R. 
Published: April 2011

ABSTRACTThe performances of amorphous and nano-crystalline porous silicon thin films as gas detector are pioneer reported in this work. The films were produced by the hot wire chemical vapour deposition (HW-CVD). These films present a porous like-structure, which is due to the uncompensated bonds and oxidise easily in the presence of air. This behaviour is a problem when the films are used for solar cells or thin film transistors. For as gas detectors, the oxidation is a benefit, since the CO, H2 or O2 molecules replace the OH adsorbed group. In the present study we observe the behaviour of amorphous and nano-crystalline porous silicon thin films under the presence of ethanol, at room temperature. The data obtained reveal a change in the current values recorded by more than three orders of magnitude, depending on the film preparation condition. This current behaviouris due to the adsorption of the OH chemical group by the Si uncompensated bonds as can be observed in the infrared spectra. Besides that, the current response and its recover time are done in few seconds.
Structural Characterization of SiF4, SiH4 and H2 Hot-Wire-Grown Microcrystalline Silicon Thin Films with Large Grains
Authors: Gutierrez J. J. , Inglefield C. E. , An C. P. , DeLong M. C. , Taylor P. C. , Morrison S. , Madan A. 
Published: April 2011

ABSTRACTIn this paper, we present a comprehensive study of microcrystalline silicon thin film samples deposited by a novel growth process intended to maximize their grain size and crystal volume fraction. Using Atomic Force Microscopy, Raman spectroscopy, and x ray diffraction the structural properties of these samples were characterized qualitatively and quantitatively. Samples were grown using a Hot-Wire Chemical Vapor Deposition process with or without a post-growth hot-wire annealing treatment. During Hot-Wire Chemical Vapor Deposition, SiF4 is used along with SiH4 and H2 to grow the thin films. After growth, some samples received an annealing treatment with only SiF4 and H2 present. These samples were compared to each other in order to determine the deposition conditions that maximize grain size. Large microcrystalline grains were found to be aggregates of much smaller crystallites whose size is nearly independent of deposition type and post-annealing treatment. Thin films deposited using the deposition process with SiF4 partial flow rate of 2 sccm and post-growth annealing treatment had the largest aggregate grains ∼.5 µm and relatively high crystal volume fraction.
VHF Large Area Plasma Processing on Moving Substrats
Authors: Kuske J. , Stephan U. , Terasa R. , Brechtel H. , Kottwitz A. 
Published: April 2011

ABSTRACTThe production of amorphous and microcrystalline silicon, e.g. for solar cells, requires large area, high-deposition rate plasma reactors. Increasing the frequency from the conventional 13.56MHz up to VHF has demonstrated higher deposition and etch rates and lower particle generation, a reduced ion bombardement and lower breakdown, process and bias voltages. But the use of VHF for large area systems leads to some problems. The non-uniformity of deposition rate increases due to the generation of standing waves and evanescent waveguide modes at the electrode surface. One possibility to process large area substrates is the use of a one-dimensional extended, homogeneous plasma source in combination with a moving substrate. The requirements, which result from the deposition process and from the RF-engineering, corresponds with the developed plasma source, using deposition frequencies in the VHF-range (50-100 MHz), almost perfectly.Using a source of 550mm length experiments were done with 81.36MHz at RF power densities of 70-180mW/cm2, silane/ hydrogen pressures of 5-30Pa and flow rates of 10-300sccm. The measured potential distribution error was ±2%. Optical emission spectroscopy delivered discharge intensity errors of ±3-10%. Deposition rates up to 20µm/h for amorphous silicon (60Å/s) and film thickness inhomogenities less than ±5% were achieved (with an area of the moved substrate of 30cm–30cm). Experimental results of the film properties will be discussed in relation to the deposition parameters and compared with complementary experiments, carried out on a small scale equipment with excitation frequencies up to 165 MHz.
Electrical Properties of Solid Phase Crystallized Silicon Films
Authors: Watanabe Tadashi , Watakabe Hajime , Sameshima Toshiyuki 
Published: April 2011

ABSTRACTIn this study, the carrier mobility and density for solid phase crystallized (SPC) silicon films fabricated at 600 °C for 48 hours are analyzed by free carrier optical absorption. The carrier mobility is 40 cm2/Vs for SPC films doped with 6×1019-cm−3-phosphorus atoms. This analysis suggests the SPC films have fine crystalline grains closed to single crystalline silicon. In addition, initial carrier density was 3×1019 cm−3, which increased to 6×1019 cm−3by XeCl excimer laser irradiation of 500mJ/cm2. The inactivated regions in SPC films are reduced by laser irradiation. However, the electrical conductivity after laser irradiation for SPC films doped with 6×1018-cm−3-phosphorus atoms decreased from 3.3 to 0.018 S/cm as laser energy density increased to 500mJ/cm2. On the other hand, the electrical conductivity increased from 14.7 to 31.3 S/cm with similar increase of laser energy density after H2O vapor heat treatment at 260°C for 3 hours with 1.3 MPa. Furthermore, the characteristics of n-channel TFTs fabricated with initial SPC films as well as SPC films which was irradiated by laser at 425mJ/cm2 are also researched. The threshold voltage is decreased from 3.8 to 2.0 V by laser irradiation. Threshold voltages of both cases are decreased from 3.8 to 2.4 V for no-laser irradiation and from 2.0 to 0.8 V for laser irradiation, after H2O vapor heat treatment at 310°C for 1 hour with 9.0MPa. Based on the above trial, the defect reduction method combining laser irradiation and H2O vapor heat treatment has proved to be very effective for SPC films and SPC TFTs.
Influence of chemical bath deposition parameters on the formation of CuInS2 / Zn(Se,O) junctions for thin film solar cells
Authors: Chaparro A.M. , Gutiérrez M.T. , Herrero J. , Klaer J. 
Published: April 2011

ABSTRACTThin film solar cells of CuInS2/Zn(Se,O)/ZnO configuration have been studied as a function of the Zn(Se,O) buffer layer deposition parameters. Deposition of the buffer films was carried out by the chemical bath deposition (CBD) method, at different bath temperatures and compositions, and followed in situ with a quartz crystal microbalance. The CBD conditions were chosen to grow Zn(Se,O) buffer layers under different kinetic regimes but maintaining the same buffer thickness. The cells have been characterised with current-voltage and quantum efficiency measurements. Light soaking effects and medium term stability have been checked. It is found that Zn(Se,O) grown under predominant electroless kinetics gives rise to buffer films richer in oxygen, which allow for higher fill factors, higher efficiencies (around 10%) and stability of the cells. These cells show however lower open circuit potential. On the other hand, Zn(Se,O) buffers grown under chemical regime become richer in selenium, which gives rise to cells with higher open circuit potential, but lower fill factor, conversion efficiency and stability. Light soaking effects are also more important with the chemically grown buffers.
High-Energy Electron and Proton Irradiation of Cu(In,Ga)Se2Heterojunction Solar Cells
Authors: Jasenek A. , Boden A. , Weinert K. , Balboul M. R. , Schock H. W. , Rau U. 
Published: April 2011

ABSTRACTWe investigate radiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after 1-MeV electron and 4-MeV proton irradiation. We use electron and proton fluences of more than 1018cm−2and up to 1014cm−2, respectively. The irradiation experiments performed at three independent electron irradiation facilities consistently prove the superior radiation resistance of these Cu(In,Ga)Se2devices compared to other types of solar cells. The reduction of the solar cell efficiency in all experiments is predominantly caused by a lossΔVOCof the open circuit voltageVOC. An analytical model describesΔVOCin terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2absorber material. From our model we extract the defect introduction rates for recombination centers in Cu(In,Ga)Se2for the respective particles and energies. Isochronal annealing stepsfully recover VOCof the irradiated Cu(In,Ga)Se2solar cells. Exposure to temperatures of approx. 400 K are sufficient to restore the initialVOCwithin less than 5 %, even after excessive irradiation. The annealing process displays an activation energy ofEA= 1.1 eV. Admittance spectroscopy directly reveals the generationandthe annealing of radiation-induced defects.
Comparative study of the structural and optical properties of CIS films prepared by RFmagnetron sputtering and selenization of elemental layers
Authors: Cunha António F. , de Azevedo M.M. Pereira , Ferrão Ricardo J.O. , Lourenço A.A.C.S. , Boemare Claude 
Published: April 2011

ABSTRACTWe report on a study where the properties of films obtained by RF-magnetron sputtering and by Selenization of elemental precursor layers are analysed by Raman scattering, x-ray diffraction and optical measurements. Three routes were followed to prepare CIS films on glass. CIS type-I was prepared by selenization at various temperatures, CIS type-II was prepared by RF-magnetron sputtering on room temperature substrate followed by annealing at 450°C in air for 10 min and CIS type-III was prepared by RF-magnetron sputtering on a substrate at a temperature ranging from 200°C up to 500°C with a post-deposition annealing in the same conditions as for CIS type-II. Correlating the results from x-ray diffraction with the Raman scattering and optical measurements it was possible to establish unequivocally the formation of CIS with the chalcopyrite structure for CIS type-I at 400°C. Through the same procedure it was possible to establish a way to produce CIS type-II with the chalcopyrite structure. A high density of defects was inferred from the transmission results. Finally the growth dynamics of CIS type-III was studied. It was observed a structural/compositional transition around substrate temperature of 300°C. It was observed that all the films had a sphalerite structure even for the highest substrate temperatures. It was establish the need for a post-deposition annealing to obtain CIS type-III with the chalcopyrite structure. The Raman scattering was found to be a very sensitive technique that allowed us to uncover a difference in the CIS type-I and II with the chalcopyrite structure.
Engineered tantalum aluminate and hafnium aluminate ALD films for ultrathin dielectric films with improved electrical and thermal properties
Authors: Clark-Phelps Robert B. , Srivastava Anuranjan , Cleveland Lance , Seidel Thomas E. , Sneh Ofer 
Published: April 2011

ABSTRACTContinued scaling of device dimensions requires deposition of high-quality thin films with a thickness of 50 angstroms or less. Nucleation effects in typical CVD processes make it difficult to achieve continuous films in this thickness regime. Atomic layer deposition (ALD), a technique developed over 25 years ago but applied to IC processing only recently, enables deposition of ultra-thin films with atomic-scale precision. This technique offers 100 percent step coverage of high aspect ratio features, as-deposited films which are amorphous and free of pinholes, excellent within-wafer uniformity and wafer-to-wafer uniformity, and favorable electrical properties. Moreover, ALD offers the opportunity to engineer material properties by creating layered structures (nanolaminates) and mixtures (alloys) which combine advantageous properties of different materials. These last features may be critical in efforts to replace silicon dioxide as the industry's dielectric workhorse if no single material emerges as a suitable direct replacement. The nanolaminate capability of ALD will be discussed with physical and electrical data on nanolaminates of aluminum oxide with tantalum pentoxide and aluminum oxide with hafnium oxide. Individual nanolaminate layers can be varied from tens of angstroms to as little as 1-2 atomic layers. Data for Al2O3/Ta2O5and Al2O3/HfO2alloys will also be presented demonstrating the ability to create materials with controlled, variable composition. The alloy and nanolaminate capabilities enable the creation of graded interfaces and atomically smooth transitions between different materials. Prospects for application of these materials to gate stacks and capacitors will be assessed.
Electricaland Structural Characteristics Of Ultra-Thin TiO2/Ti-Si-O Stacked Gate Insulator Formed by Rf Sputtering Technique
Authors: Koyama M. , Kaneko A. , Koike M. , Fujiwara I. , Yabuki M. , Yoshiki M. , Koike M. , Nishiyama A. 
Published: April 2011

ABSTRACTIn this paper, we have reported an attempt to decrease equivalent oxide thickness (EOT) of TiO2gate insulator by thinning the amorphous layer formed at the TiO2/Si interface. We have decreased the thickness of the TiO2/Si interfacial layer to as little as 1.6 nm by suppressing the oxygen flow rate during the TiO2 sputtering. It was confirmed that the dielectric constant of the interfacial layer revealed higher value than that of SiO2, depending on the sputtering condition. Titanium in the interfacial layer, which was responsible for the polarization enhancement, was explicitly identified by high spatial resolution TEM-EELS. As a result, EOT of 1.3 nm was realized by TiO2/Ti-Si-O stacked gate insulator without any degradation in the electrical characteristics.
A Study on the Polycrystalline Silicon Germanium Gate Electrode Fabrication Technology for Cobalt Silicide Process
Authors: Sato Hidekazu , Sukegawa Takae , Mori Toshifumi , Suzuki Kousuke , Mori Haruhisa 
Published: April 2011

ABSTRACTThis paper reports the dependence on the concentration of the germanium (Ge) in polycrystalline silicon (poly-Si) cap layer on the polycrystalline silicon germanium (poly-SiGe) for low resistivity cobalt disilicide (CoSi2) formation. Particularly, we investigate the relationship between sheet resistance of CoSi2 films and concentration of Ge in cap-Si layer. The excellent value of sheet resistance (∼6 / ) is achieved by Ge concentration in cap-Si layer controlled at 2% or less for 90nm length CoSi2/poly-Si/poly-SiGe gate structure. This result indicates that conventional Co silicide process technology can be readily used even for poly-SiGe gate structure.