bluuebunny/crossref_metadata_2025 huggingface dataset:
SiC Power Devices
Authors: Chow T. P. , Ghezzo M.
Published: April 2011

The present status of SiC high-voltage power switching devices is reviewed. The figures of merits that have been used for unipolar and bipolar devices to quantify the intrinsic performance improvement over silicon are presented. Analytical and numerical modeling and simulations to estimate the BV and device choice are described. The active area and termination design of trenched-gate MOS power transistors, together with an integrated process for their fabrication, is presented. The progress in high-voltage power device experimental demonstration is described. The material and process technology issues that need to be addressed for SiC device commercialization are discussed. Finally, the impact of SiC power devices on motor drive systems is estimated.
Low Temperature Growth of Nanocrystalline Silicon From SiF4 + SiH4
Authors: Chen Yu , Taguchi M. , Wagner S.
Published: April 2011

The electrical conductivity of nc-Si films grown from SiF4 and H2 with constant arsenic doping rises from 10-5 to 10 Scm-1 as the thickness rises from ˜ 0.1 to 1 μm. This variation demonstrates the strong influence of film structure on conductivity. We show that the conductivity of undoped nc-Si films of constant thickness can be varied by adding SiH4 to the SiF4 and H2 source gas.
Hydrogen Behavior in PECVD Nitride by SiH4 & ND3 During RTA
Authors: He S. S. , Shannon V. L. , Nguyen T.
Published: April 2011

PECVD silicon nitride was deposited by silane and deuterium ammonia. Silicon rich and nitrogen rich silicon nitride were deposited by varying the ratio of the SiH4/DH3. From FTIR, we found that the wave numbers of SiD and ND shifted lower when compared to SiH and NH bond in the NH3 nitride. In Si-rich nitride, both Si-H and Si-D bonds were found, which is different from N-rich nitride, where only an ND bond was found. Most of the hydrogen in NH(D) comes from the ammonia during PECVD deposition. We found that some of the deuterium exchanges its bonding to silicon from the initial bonding to nitrogen during a rapid thermal annealing process.
Ac and Dc Characterization and Spice Modeling of Short Channel Polysilicon Tfts
Authors: Jacunski M. D. , Shur M. S. , Ytterdal T. , Owusu A. A. , Hack M.
Published: April 2011

We present an analytical SPICE model for the AC and DC characteristics of n and p channel polysilicon TFTs which scales fully with channel length and width in all regimes of operation (leakage, subthreshold, above threshold, and kink) and accounts for the frequency dispersion of the capacitance. Once physically based parameters have been extracted from long channel TFTs, which include the gate length and drain bias dependencies of the device parameters, our model accurately reproduces short channel device characteristics. The AC model includes the input channel resistance in series with the gate oxide capacitance. As a result, our model is able to fit the frequency dispersion of the device capacitances. The model has been implemented in the AIM-Spice simulator and good agreement is observed between measured and modeled results for gate lengths down to 4 gim.
Copper-Enhanced Solid Phase Crystallization of Amorphous Silicon Films
Authors: Sohn Dong Kyun , Moon Dae Gyu , Ahn Byung Tae
Published: April 2011

Low-temperature crystallization of amorphous Si (a-Si) films was investigated by adsorbing copper ions on the surface of the films. The copper ions were adsorbed by spincoating of Cu solution. This new process lowered the crystallization temperature and reduced crystallization time of a-Si films. For 1000 ppm solution, the a-Si film was partly crystallized down to 500°C in 20 h and almost completely crystallized at 530°C in 20 h. The adsorbed Cu on the surface acted as a seed of crystalline and caused fractal growth. The fractal size was varied from 10 to 200 prm, depending on the Cu concentration in solution. But the grain size of the films was about 400 nm, which was similar to that of intrinsic films crystallized at 600°C.
Comparison Between Rapid Thermal and Furnace Annealing for A-Si Solid Phase Crystallization
Authors: Kingi Reece , Wang Yaozu , Fonash Stephen J. , Awadelkarim Osama , Mehlhaff John
Published: April 2011

Rapid thermal annealing and furnace annealing for the solid phase crystallization of amorphous silicon thin films deposited using PECVD from argon diluted silane have been compared. Results reveal that the crystallization time, the growth time, and the transient time are temperature activated, and that the resulting polycrystalline silicon grain size is inversely proportional to the annealing temperature, for both furnace annealing and rapid thermal annealing. In addition, rapid thermal annealing was found to result in a lower transient time, a lower growth time, a lower crystallization time, and smaller grain sizes than furnace annealing, for a given annealing temperature. Interestingly, the transient time, growth time, and crystallization time activation energies are much lower for rapid thermal annealing, compared to furnace annealing.

We propose two models to explain the observed differences between rapid thermal annealing and furnace annealing.
Polycrystalline Silicon Films Formed by Solid-Phase Crystallization of Amorphous Silicon: the Substrate Effects on Crystallization Kinetics and Mechanism
Authors: Song Y.-H. , Kang S.-Y. , Cho K. I. , Yoo H. J. , Kim J. H. , Lee J. Y.
Published: April 2011

The substrate effects on the solid-phase crystallization of amorphous silicon (a-Si) have been extensively investigated. The a-Si films were prepared on two kinds of substrates, a thermally oxidized Si wafer (SiO2/Si) and a quartz, by low-pressure chemical vapor deposition (LPCVD) using Si2H6 gas at 470 °C and annealed at 600 °C in an N2 ambient for crystallization. The analysis using XRD and Raman scattering shows that crystalline nuclei are faster formed on the SiO2/Si than on the quartz, and the time needed for the complete crystallization of a-Si films on the SiO2/Si is greatly reduced to 8 h from ˜15 h on the quartz. In this study, it was first observed that crystallization in the a-Si deposited on the SiO2/Si starts from the interface between the a-Si film and the thermal oxide of the substrate, called interface-induced crystallization, while random nucleation process dominates on the quartz. The very smooth surface of the SiO2/Si substrate is responsible for the observed interface-induced crystallization of a-Si films.
TMCTS for gate dielectric in thin film transistors
Authors: Wang Albert W. , Bhat Navakanta , Saraswat Krishna C.
Published: April 2011

The use of the liquid source tetramethylcyclotetrasiloxane (TMCTS) for gate dielectric deposition in low-temperature polysilicon thin film transistor (TFT) processes is investigated. TMCTS was reacted with O2 in an LPCVD furnace at 580°C to form a gate dielectric. For comparison, a low temperature oxide (LTO) was deposited as a gate dielectric using SiH4−O2 LPCVD at 450°C. Capacitance and charge pumping measurements indicate fewer interface states for TMCTS gate dielectric. Both NMOS and PMOS TFTs show comparable or superior performance with TMCTS oxide. Post-deposition annealing has less effect on TMCTS gate oxides. Although TMCTS gate dielectrics appear slightly more susceptible to damage in biastemperature stress tests, TFTs with TMCTS gate oxides still retain better performance after stressing.
Liquid-crystals for multimedia display use: materials and their physical properties
Authors: Naemura S.
Published: April 2011

Display devices are one of the key elements of the coming multimedia infrastructure, and Thin-Film-Transistor addressed Liquid Crystal displays are most promising for this application. Physical properties such as dielectric permitivities and electric resistivity are essentially important for TFT-addressing use LC materials. Both theoretical and experimental studies on these properties are reviewed and discussions are made on these in relation to the chemical structure of the liquid crystal substances, providing semiquantitative explanations on the superiority of fluorinated LC materials in respect to the coexistence of the high polarity and the high resistivity. Further studies to improve LC material properties are finally suggested.
Suspended particle display using novel complexes
Authors: Takeuchi H. , Usuki A. , Tatsuda N. , Tanaka H. , Okada A. , Tojima K.
Published: April 2011

Suspended particle display (SPD) can be controlled in transparency by applying a.c. voltage. We found new synthesized particles for SPD and methods for making them fine. Three new SPD particles showing different colors have been found: δ-herapathite, 1,10-phenanthroline-iodine complex and pyrazinophenanthroline-iodine complex as showing red, blue, purple, respectively. Recrystallization and ultrasonic treatment were found to make them fine crystals. Accordingly, transparency, stability for sedimentation and thermal stability were improved.
Effect Of Base Pressure In Sputter Deposition On Characteristics Of Indium Tin Oxide Thin Film
Authors: Lee Byung Hak , Yi Choong-Hoon , Kim Lee Gon , Lee Si-Hyun
Published: April 2011

A novel approach to sputter deposit low resistivity indium tin oxide thin films in cost effective way has been made. To reduce the complication of out-gassing from organic substances that are deposited at prior process steps in the flat panel display manufacturing, DC+RF magnetron sputtering was performed with a relatively high base pressure. Introduction of impurity atoms originated from residual air in the chamber into the film produced the change in lattice as well as microstructure of the film. Sputter deposition with higher base pressure resulted in lower resistivity of the film. Increase in the mobility of the carrier resulted in resistivity decrease. Resistivity as low as 1.5×10−4 Ω cm has been achieved with DC 0.67 W/cm2 + RF 0.67 W/cm2 power density and 10−5 Torr base pressure. X-ray diffraction analysis showed as much as 0.2 % increase in lattice constant resulted from higher base pressure sputtering. No further improvement of conductivity was observed for the base pressure over 10−5 Torr, suggesting impurity introduction saturation into the film.
Gold Overcoatings on Spindt-Type Field Emitter Arrays
Authors: Skala S. L. , Ohlberg D. A. , Talin A. A. , Felter T. E.
Published: April 2011

The electron emission properties of a Spindt-type field emitter array have been measured before and after deposition of approximately 100 Å of gold. The workfunction of the emitter decreased by 5% after gold deposition resulting in an 11% reduction in turn-on voltage. Emission stability as measured by RMS current noise improved by 40%. Improvements in emission do not withstand exposure to air. However, baking at moderate temperatures (200°C) restores the emission improvements obtained with the gold overcoating. Fowler-Nordheim plots show that the enhanced emission after baking is due to a increase of the Fowler-Nordheim intercept and not a decrease in slope. Additionally, the gold over coatings resist poisoning as a 50,000 L dose of oxygen only slightly affects emission.
High-Rate Deposited Amorphous Silicon Nitride for the Hydrogenated Amorphous Silicon Thin-Film Transistor Structures
Authors: Li Tong , Chen Chun-Ying , Malone Charles T. , Kanicki Jerzy
Published: April 2011

Hydrogenated amorphous silicon nitride thin films, prepared in a large area plasma-enhanced chemical vapor (PECVD) deposition system utilizing high-rate deposition technique, have been characterized by various techniques. Experimental data obtained from this study are presented and compared to low-rate deposited PECVD films. Special attention has been devoted during this study to the difference between high- and low-rate deposited samples. The amorphous silicon (a-Si:H) thin-film transistors (TFTs) based on high-rate PECVD materials have been fabricated and characterized. The evaluation of a-Si:H TFTs indicates a good electrical performance which is comparable to its low-rate PECVD materials counterparts.
Variation of Luminescent Efficiency With Size of Doped Nanocrystalline Y203:Tb Phosphor
Authors: Goldburt E. T. , Kulkarni B. , Bhargava R. N. , Taylor J. , Libera M.
Published: April 2011

In doped nanocrystalline Y203:Tb phosphors the luminescent efficiency was found to increase with the decrease in the particle size from 100 Å to 40 Å. This correlation was obtained from microstructural studies performed using transmission electron microscopy and luminescent measurements.
TiO2:Ce/CeO2 High Performance Insulators For Thin Film Electroluminescent Devices
Authors: Bally A. R. , Prasad K. , Sanjinés R. , Schmid P. E. , Lévy F. , Benoit J. , Barthou C. , Benalloul P.
Published: April 2011

The electrical properties of titanium dioxide thin films have been stabilised by cerium doping. These films have a high permittivity between 35 to 45 and withstand 650°C. Multilayer TiO2:Ce/CeO2 insulators have been fabricated. The breakdown voltage is increased by a factor 10 with a modest decrease in the permittivity (30 – 35 instead of 35 – 45).

Electroluminescent devices (ELDs) with a classical ZnS:Mn phosphor have been prepared using TiO2:Ce as the first insulator and a TiO2:Ce/CeO2 multilayer as the second insulator. Compared with a standard ELD based on Y2O3 insulators, devices with the new insulators show a significant decrease of the threshold voltage along with a notable increase of the brightness. An important increase is also achieved in the total device efficiency which is maintained over a large range of brightness and transferred charge. Consequences of rapid thermal annealing and conventional thermal treatments on device performance have also been investigated.
Silicon Nanoclusters In Silica: A Luminescence Study Of Visible Light Emission From A Siliconbased Material
Authors: Trwoga P. F. , Kenyon A. J. , Pitt C. W.
Published: April 2011

Considerable interest has been generated recently in the application of Porous Silicon to the production of light emitting devices, and a number of demonstration structures have been produced. However, the poor stability of the material pose limitations on its usefulness. We report studies of the luminescence properties of a related, but stable material: silicon-rich silica. This material consists of silicon clusters embedded in a host matrix of silica, and as such is considerably more robust than porous silicon.

We have produced a number of samples of silicon-rich silica thin films by Plasma Enhanced Chemical Vapour Deposition on to doped silicon substrates. We report photoluminescence studies that investigate the nature of the radiative process, and show evidence of two separate luminescence mechanisms: defect luminescence and exciton confinement in nanoscale silicon clusters. Preliminary electroluminescence from silicon-rich silica fabricated by Plasma Enhanced Chemical Vapour Deposition will also be presented.
Amorphous Silicon TFTs on Steel-Foil Substrates
Authors: Theiss S. D. , Wagner S.
Published: April 2011

We describe the successful fabrication of device-quality a-Si:H thin-film transistors (TFTs) on stainless-steel foil substrates. These TFTs demonstrate that transistor circuits can be made on a flexible, non-breakable substrate. Such circuits could be used in reflective or emissive displays, and in other applications that require rugged macroelectronic circuits.

Two inverted TFT structures have been made, using 200 gim thick stainless steel foils with polished surfaces. In the first structure we used the substrate as the gate and utilized a homemade mask set with very large feature sizes: L = 45 μm; W = 2.5 mm. The second, inverted staggered, structure used a 9500 Å a-SiNx:H passivating/insulating layer deposited on the steel to enable the use of isolated gates. For this structure we used a mask set which is composed of TFTs with much smaller feature sizes. Both TFT structures exhibit transistor action. Current-voltage characterization of the TFTs with the inverted staggered structure shows typical on/off current ratios of 107, leakage currents on the order of 10-12A, good linear and saturation current behavior, and channel mobilities of 0.5 cm2/V·sec. These characteristics clearly identify the TFTs grown on stainless steel foil as being of device quality.
Vitrification and Morphological Stability of Liquid Crystals
Authors: Mastrangelo J. C. , Chen S. H. , Blanton T. N. , Bashir-Hashemi- A.
Published: April 2011

Based on the extensive database collected for model glass-forming liquid crystals with various mesogenic groups attached to benzene, cubane, cis- and trans-cyclohexane, and all-exobicyclo[ 2.2.2]oct-7-ene, it was found that the glass-forming ability and morphological stability are determined by a delicate structural balance between the volume-excluding core and the pendant group, and the stereochemical features of the hybrid system.
Photorefractivity and Holographic Storage Effect in Fullerene C60-Doped Nematic Liquid Crystals
Authors: Khoo I. C. , Wood M. V. , Guenther Brett D.
Published: April 2011

The results of a recent study of a nonlinear electro-optical effect in fullerene C60-doped nematic liquid crystal film are presented. In particular, photo-induced conduction, self diffraction effect, and permanent holographic formation in the films are explained.
Model Systems for Liquid Crystal Based Dispersed Heterogeneous Materials
Authors: Aliev F. M. , Sinha G. P.
Published: April 2011

Porous matrices with determined pore size, volume fraction and structure can be used as model systems to understand physical properties of dispersed liquid crystals (LC) - material important for different applications. Using photon correlation spectroscopy and dielectric spectroscopy we investigated dynamic properties of nematic liquid crystal dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses with average pore sizes of 100 Å and 1000 Å) and parallel cylindrical pores (Anopore membranes with pore diameters of 200 Å and 2000 Å). Since the structural characteristics of these matrices are nearly independent of the temperature, all observable effects due to temperature changes can be attributed to the change in the physical properties of the second component (bC). The spatial confinement and a highly developed interface in porous matrices have a strong influence on the optical and dielectric properties of confined LC which is resulted in: appearance of at least two new dielectrically active modes, absent in the bulk and existence of slow glass-like relaxational process detected in both dielectric and photon correlation experiments.
Synthesis of Thin Films by Polymerization of Liquid Crystalline Monomers
Authors: Kurihara S. , Iwamoto K. , Nonaka T.
Published: April 2011

Mixtures of mono- and diacrylates showing a nematic phase were polymerized in an electric field. The orientation of chromophores in the thin films depended on the direction of dipole moment as well as the polymerization conversion of the liquid crystalline monomers.
Inhibition of Metal Induced Crystallization in the System Ag/ZnO/a-Si:H
Authors: Edelman F. , Brener R. , Cytermann C. , Weil R. , Beneking C. , Beyer W.
Published: April 2011

A systematic investigation has been made on the barrier properties of ZnO layer between ndoped a-Si:H and Ag metallization films in the structures (001)Si/SiO2/Ag/ZnO/a-Si:H:P and (001)Si/SiO2/a-Si:H:P/ZnO/Ag. Plasma assisted CVD deposition was used to produce a-Si:H (2500Å thick) highly P-doped films over thermally oxidized Si-wafers at 190 and 270°C. Transparent conductive ZnO:AI layers, 1000Å and lμm thickness, and Ag films (1000Å thick) were deposited by sputtering. The polycrystalline ZnO layers were textured along the <0001> axis in the as-deposited state. The structures were annealed in vacuum in the temperature range from 300 to 700°C for 1/4 to 16h. X-ray diffraction and transmission electron microscopy studies demonstrated the a-Si:H:P stability against crystallization under ZnO buffer protection up to 700°C (when free a-Si crystallizes itself). The (111) peak position of the Ag reflection was used to show that while the Ag was always strained, the strain was partially relaxed when in contact with the 0. 1μm ZnO film, it developed additional strain when in contact with the 1μm ZnO film.
The Performance of Cu(In, Ga)Se2-Based Solar Cells in Conventional and Concentrator Applications
Authors: Tuttle J. R. , Ward J. S. , Duda A. , Berens T. A. , Contreras M. A. , Ramanathan K. R. , Tennant A. L. , Keane J. , Cole E. D. , Emery K. , Noufi R.
Published: April 2011

Cu(In, Ga)Se2 (CIGS) solar cells are under investigation for 1-sun and concentrator applications. Design criteria are examined and reveal that only grid design modifications are required. In the special case where cell width dimensions are 4–5 cm, an interdigitated design removes the back contact as a loss mechanism. Processing issues relating to the intrinsic ZnO layer are critical to optimal and reproducible cell performance. 1-sun and 20 sun performance of 17.7% are reported for different cells. The latter represents a 2.9% absolute improvement over the 1-sun control measurement. 20% performance is therefore a realistic goal. CIGS-based cells represent a viable concentrator technology.
Advanced Stacked Elemental Layer Process for Cu(InGa)Se2 Thin Film Photovoltaic Devices
Authors: Probst V. , Karg F. , Rimmasch J. , Riedl W. , Stetter W. , Harms H. , Eibl O.
Published: April 2011

Targeting large area and low cost processing of highly efficient thin film solar modules an advanced stacked elemental layer process for Cu(InGa)Se2 (CIGS) thin films is presented. Key process steps are i) barrier coating of the soda lime glass substrate combined with the addition of a sodium compound to the elemental Cu/In/Ga/Se-precursor stack and ii) rapid thermal processing (RTP) to form the CIGS compound.

By this strategy exact impurity control is achieved and the advantageous influence of sodium on device performance and on CIGS film formation is demonstrated unambiguously by means of electrical characterisation, XRD, SEM, TEM and SIMS. Sodium enriched and sodium free precursor stacks were heated to intermediate states (300°C–500°C) of the RTPreaction process. The experiment clearly reveals that on the reaction pathway to the chalcopyrite semiconductor increased amounts of copper-selenide are formed, if sodium is added to the precursor films. TEM-electron diffraction unambiguously identifies the CuSe-phase which is localised at the surface of the forming CIGS-film. These experimental findings propose a sodium assisted quasi liquid growth model for the CIS formation taking into account that sodium promotes the existence of CuSe at higher temperatures and its effect as a flux agent. The model contributes to a better understanding of the observed superior crystal qualitiy for sodium enriched in contrast to sodium free CIGS films.

Application of these experimental findings in the technique of the optimized and controlled sodium incorporation significantly improves process reproducibility, CIGS film homogenity over larger substrate areas and shifts the average efficiency of cells and modules to a significantly higher level. This is demonstrated by a 12-cell integrated series connected minimodule with an aperture area of 51 cm2 and a confirmed efficiency of 11.75 %.
Formation Chemistry of Polycrystalline Cu(InGa)Se2 Thin-Film Absorbers Prepared by Selenization of Cu-Ga/In Stacked Precursor Layers with H2Se Gas
Authors: Kushiya K. , Kuriyagawa S. , Kase T. , Sugiyama I. , Tachiyuki M. , Takeshita H.
Published: April 2011

The purpose of this study is to improve the reliability and reproducibility of our fabrication process for polycrystalline Cu(InGa)Se2 (CIGS) thin-film absorbers and to make a better absorber with higher efficiency. The current baseline process of selenization has been evaluated through the investigation of the formation chemistry of the device-quality CIGS thin-film absorbers with a graded band-gap structure. It has been verified that the current selenization process has been performed in a good balancing point with both Cu/III ratio and thickness of the precursor layer and the total amount of Se through H2Se gas incorporated from the surface during the selenization. A simplified model to explain the formation chemistry of the selenization in this study has been proposed.
Investigation of Electrochemical Processes for Synthesis and Removal of CuInSe2 Thin Films
Authors: Menezes Shalini
Published: April 2011

Electrochemical deposition of CuInSe2 films has been explored as a low-cost alternative to vacuum deposition. A special feature of this approach is that each element or compound may be selectively deposited or dissolved at a specific potential. This approach could further provide an environmentally benign means to recycle CuInSe2 from spent or defective modules. The paper investigates the reaction mechanisms for co-deposition, as well as, removal of CuInSe2. Rotating ring-disk and photoelectrochemical methods probe the formation and dissolution of Se, Cu2Se, In2Se3 and CuInSe2 films and the corrosion of CuInSe2 single crystal. The results provide important insights into the multiple reaction paths leading to the electrosynthesis of CuInSe2 films and new directions for developing an electrochemical recycling scheme for CuInSe2 modules.
The Effects of Kcn Etching on Cu-Rich Epitaxial CuInSe2 Thin Films
Authors: Fons P. , Nikl S. , Yamada A. , Nishitanp M. , Wada T. , Kurafuji T.
Published: April 2011

A series of Cu-rich CuInSe2 epitaxial thin films were grown by molecular beam epitaxy on GaAs(001) substrates from elemental sources at a growth temperature of 450 °C. All samples were grown with an excess of Cu. Electron microprobe analysis (EPMA) indicated a Cu/ In ratio of about 2.1–2.6 in the as-grown films. Additionally, the Se/ (In+Cu) ratio was observed to be ∼0.95 indicating that the films were slightly Se poor. These Cu-rich samples were etched in a KCN solution for periods ranging from 30 seconds to 3 minutes. EPMA measurements indicated that the bulk Cu/ In ratio was reduced to ∼0.92 in all films regardless of etching time. Atomic force microscopy (AFM) was used to characterize the topology of each sample before and after etching. These measurements indicated that the precipitates present on the as-grown films were removed and large nearly isotropic holes were etched into the sample to a depth of over 1000 Å even for etching times as short as 30 seconds. The samples were also evaluated both before and after etching using a Phillips MRD diffractometer with parallel beam optics and a 18,000 watt Cu rotating anode X-ray source in the chalcopyrite [001], [101], and [112] directions. A peak was observed at ∼15 degrees in the [001] scan after etching consistant with the presence of the ordered vacancy compound, CuIn3Se5. Additionally the integrated intensity ratios of the chalcopyrite (202) reflection to the chalcopyrite (101) reflection ∝(fCu-fIn)2 along the [101] direction indicated the presence of a near-surface region containing cation sublattice disorder that was subsequently removed by the etching process.
Defect Chalcopyrite Cu(In1-x, Gax)3Se5 Polycrystalline Thin-Film Materials
Authors: Contreras Miguel A. , Wiesner Holm , Matson Rick , Tuttle John , Ramanathan Kannan , Noufi Rommel
Published: April 2011

The defect chalcopyrite material CuIn3Se5 has been identified as playing an essential role in efficient photovoltaic action in CuInSe2-based devices; it has been reported to be of n-type conductivity, forming a p-n junction with its p-type counterpart CuInSe2. Because the most efficient cells consist of the Cu(In1-xGax)Se2 quaternary, knowledge of some physical properties of the Ga-containing defect chalcopyrite Cu(In1-xGax)3Se5 may help us better understand the junction phenomena in such devices.

Polycrystalline Cu(Inl-xGax)3Se5 (with O<x<l) thin films have been grown on 7059 Coming glass, soda-lime silica glass, n-type (100)Si, and Mo-coated soda-lime glass by coevaporation from elemental sources. In general, optical data show direct optical bandgaps that range from 1.20 eV for x=0 to ∼1.85 eV for x=l (this represents ∼200 meV higher bandgaps than the Cu(In, Ga)Se2 counterparts). Micrographs of the thin films show a substantial change in morphology as the Ga content is increased—for identical conditions of growth rate and substrate temperature. X-ray diffraction patterns agree with previously publish data for the ternary case (x=0), where these materials have been referred to as ordered vacancy compounds. Pole figures confirm a high degree of texturing in the films and a change in preferred orientation as Ga content is increased.
Real Time Composition Monitoring Methods in Physical Vapor Deposition oF Cu(In, Ga)Se2 Thin Films
Authors: Negami Takayuki , Nishitani Mikihiko , Kohara Naoki , Hashimoto Yasuhiro , Wada Takahiro
Published: April 2011

Three real-time composition monitoring methods in physical vapor deposition process of CIGS thin films were proposed. One is the detection of near infrared (NIR) transmittance through the CIGS films from the IR source such as a heater back side of the substrate. One is the detection of NIR reflectance of the incident light from the films. The other is the measurement of the substrate temperature during the preparation of the CIGS films. These methods utilize the difference of the carrier density between Cu-rich (∼ 1020/cm3) and (In+Ga)-rich ( > 1016/cm3) films. The NIR transmittance through and reflectance from the Cu-rich film decrease due to high free carrier absorption. The temperature of the Cu-rich films was lower than that of the (In+Ga)-rich ones under the constant heating power because the Cu-rich films have larger radiation in proportion to absorption. Therefore, the change of Cu/(In+Ga) ratios at stoichiometry can be monitored by the variation of the NIR transmittance, NIR reflectance or the film temperature in real time. These composition monitoring methods are very useful and easily applied to the physical vapor deposition process of the CIGS films for photovoltaic application. The solar cell with active area of about 0.5 cm2, fabricated by obtaining the CIGS film using the latter monitoring method, showed an efficiency of 17.0%.
Technological Development for Commercialization of Amorphous Silicon Based Multijunction Modules
Authors: Yang Liyou , Bennett M. , Chen L. , Jansen K. , Kessler J. , Li Y. , Newton J. , Rajan K. , Willing F. , Arya R. , Carlson D. , Solarex
Published: April 2011

Some of the significant steps in technological development for large-scale commercialization of amorphous silicon (a-Si:H) based multijunction photovoltaic modules are presented. These developments are establishing a high quality baseline process for manufacturing large-area ( ∼ 8 ft2) a-Si:H/a-SiGe:H tandem junction modules with improved stabilized conversion efficiency, throughput, yield, and reduced materials usage.
Intermixing at the CdS/CdTe Interface and its Effect on Device Performance
Authors: Dhere R. G. , Albin D. S. , Rose D. H. , Asher S. E. , Jones K. M. , Al-Jassim M. M. , Moutinho H. R. , Sheldon P.
Published: April 2011

A study of the CdS/CdTe interface was performed on glass/SnO2/CdS/CdTe device structures. CdS layers were deposited by chemical solution growth to a thickness of 80–100 nm, and CdTe was deposited by close-spaced sublimation at substrate temperatures of 500°, 550°, and 600°C. Post-deposition CdCl2 heat treatment was performed at 400°C. Samples were analyzed by optical spectroscopy, secondary ion mass spectrometry (SIMS), spectral response, and current-voltage measurements. SIMS analysis shows that the intermixing of CdS and CdTe is a function of substrate temperature and post-deposition CdCl2 heat treatment. The degree of intermixing increases with increases in substrate temperature and the intensity of CdCl2 heat treatment. Optical analysis and X-Ray diffraction data show that the phases of CdSxTe1-x are also a function of the same parameters. Formation of a Te-rich CdSxTe1-x alloy is favored for films deposited at higher substrate temperatures. Spectral response of the devices is affected by the degree of alloying at the interface. The degree of alloying is indicated by simultaneous changes in long wavelength response (due to the formation of lower bandgap intermixed CdSxTe1-x) and the short wavelength response (due to the change in CdS thickness). Device performance is heavily influenced by alloying at the interface. With optimized intermixing, improvements in Voc, and diode quality factors are observed in the resulting devices.
Properties of Pulsed Laser Deposited CdSxTe1-x Films on Glass
Authors: Compaan D. , Feng Z. , Contreras-Puente G. , Narayanswamy C. , Fischer A.
Published: April 2011

Interdiffusion of sulfur and tellurium across the CdS/CdTe interface is fundamentally important in the operation of CdTe solar cells. However, the properties of the resulting alloy semiconductor, CdSxTe1-x, are not well understood. We have prepared films of this ternary material by pulsed excimer laser deposition (PLD) across the alloy range. These films were examined by x-ray diffraction, wavelength dispersive x-ray spectroscopy, optical absorption, and Raman scattering to determine the influence of sulfur content on the crystal structure, lattice constant, energy gap, and vibrational mode behavior.
Preparation and Properties of Transparent Conductors
Authors: Gordon Roy G.
Published: April 2011

Transparent, electrically conductive films have been prepared from several different metal oxides, including those of tin, indium and zinc. Deposition methods for these materials are reviewed, and their properties summarized and compared. A figure of merit for a transparent conductor may be defined as the ratio of the electrical conductivity to the optical absorption coefficient of the film. The figure of merit for fluorine-doped zinc oxide is shown to be larger than that of other transparent conductors, such as boron-doped zinc oxide, fluorine-doped tin oxide, and tin-doped indium oxide. Physical, chemical and thermal durability, deposition temperature, and cost are other factors which may also influence the choice of material for a particular application.
Optical Indices of Pyrolytic Tin-Oxide Glass
Authors: Von Rottkay K. , Rubin M.
Published: April 2011

SnO2:F is a widely used transparent conductor and commercially available in a multilayer structure as Tech glass. Current applications include photovoltaics, electrochromics and displays. Optical design of these and other applications requires knowledge of the optical constants, in some cases, over the whole solar spectrum. Various optical property measurements were performed including variable angle spectroscopic ellipsometry, and spectral transmittance and reflectance measurements. This material is deposited in several steps and has a fairly complex structure. The measured data were fit to models based on this structure to obtain the optical indices. Atomic force microscopy confirmed the optically modeled surface roughness.
The Growth of Surface Textured Aluminum Doped ZnO Films for a-Si Solar Cells by RF Magnetron Sputtering At Low Temperature
Authors: Selvan J. A. Anna , Keppner H. , Shah A.
Published: April 2011

Transparent Conducting Oxide films are essential for all kind of thin film solar cells. Doped Zinc Oxide (ZnO) in particular has several advantages when compared to other TCOs. It is stable in a hydrogen plasma and it acts as a diffusion barrier with respect to impurities from the substrate. In this work results on textured ZnO films deposited by RF magnetron sputtering are presented. The dependence of the film properties on the RF power, the substrate temperature and the water-vapor partial pressure added to the argon atmosphere has been investigated. We have found that high quality textured aluminum doped ZnO (ZnO:AI) films can be grown at low temperatures (150 °C) using the sputtering technique. Textured surfaces show two types of surface morphology; columnar and granular, depending on the deposition conditions. The ZnO:AI films seem to undergo a structural transition from hexagonal (mostly columnar appearance) to cubic structure (mostly granular appearance).
Role Of Deep Level Trapping On Surface Photovoltage Of semiinsulating GaAs
Authors: Liu Qiang , Ruda Harry E. , Koutzarov Ivoil P. , Jedral Lech , Chen Genmao , Prasad Manoj
Published: April 2011

Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state EL2& was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2& recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1. 9× 1012 s−1 were obtained, and attributed to the thermal recovery rate for EL2&.
The Valence Band Tail Density of States and Bond Angle Distortion in a-SiNx: H Alloys
Authors: Budaguan B. G. , Aivazov A. A. , Stryahilev D. A
Published: April 2011

Films of a-SiNx:H with x = 0.0..0.62 were deposited by glow discharge decomposition of (10% SiH4+90%/H2 )+ NH3 mixture. The chemical bonding and composition of films were investigated with using of infrared spectroscopy. The deformation energy per Si atom connected to bond bending Vkθ was calculated from data of Raman scattering. Characteristic energy of valence band tail (VBT) states distribution, E0v, were determined fromrsubgap absorption spectra. The dependencies of E0v and Vkθ on film composition, x, were considered in order to estimate the influence of the bond angle disorder on the distribution of VBT states.

The essential difference in behavior of E0v and Vkθ dependencies on x was found for Si-rich (x<0. 15) alloys. When Vkθ value increase with x, the E0v parameter stays almost constant; while at x>0. 15 the E0v increase with x as well as the VKO. It means that bond angle disorder in the bulk of the material contributes to VBT characteristic energy, but it is not the only source. Another factors as it was shown may be connected with valence states of Si atoms, localized near inner boundaries.
A Global Electricai-Optical Model of Thin Film Solar Cells on Textured Substrates
Authors: Chatterjee P. , Leblanc F. , Favre M. , Perrin J.
Published: April 2011

In order to simulate the performance of the present day state-of-the-art multijunction solar cells in its entirety, an integrated electrical-optical model has been developed. The one-dimensional ab initio electrical model for the analysis of the transport properties of such devices can handle a very general semiconductor device structure where the material properties vary with position and the gap state properties with position and energy. The original semi-empirical optical model used takes into account both specular interference effects, and diffused reflectances and transmittances due to interface roughness. The latter are derived from angular-resolved photometric measurements and used as input parameters to the numerical programme. Comparison of the illuminated current density-voltage (J-V) characteristics, calculated on the basis of (a) a simple exponential absorption law and (b) the optical model, reveals an increase of ˜1 mA cm−2 in the short-circuit current and ˜8% in the cell conversion efficiency for case (b). Also the long wavelength quantum efficiency (QE) shows a marked improvement, while the blue QE decreases since proper account is taken of the absorption in the transparent conducting oxide and reflection from the device. The combined model is being applied to simulate the characteristics of wideband-gap-emitter-layer solar cells deposited in a three chamber conventional glow discharge reactor onto (i) highly textured SnO2 and (ii) weakly textured indium tin oxide substrates. The cells have been characterised experimentally by J-V and QE measurements. Preliminary results indicate that the integrated model matches the experimental J-V and QE data with a more realistic set of material parameters as compared to case (a).
Numerical Simulation of Surface Diffusion Controlled Motion and Shape Change of Electromigration Voids
Authors: Kraft O. , Mockl U. E. , Arzt E.
Published: April 2011

In order to simulate void motion and shape change of electromigration voids a numerical model was developed in which electromigration-driven diffusion on the void surfaces is assumed to act as the primary transport mechanism. The simulation describes the motion and shape evolution of a "two-dimensional void" having a simple initial shape in an isotropic medium. The current density distribution in the vicinity of a void was calculated by the application of a finite element method. Subsequently, the void shape changes by surface diffusion were examined using a finite difference scheme which includes the influence of gradients in curvature along the void surface. The model has been extended to allow other diffusion pathways, such as grain boundaries. The often observed faceting of voids and the formation of slit-like voids are discussed on the basis of simulations in which anisotropic surface tension and anisotropic surface diffusivity were assumed.
A Molecular Dynamics Study of Cu Segregation to the Σ11 Grain Boundary In Al
Authors: Huang Hanchen , Rubia T. Diaz de la , Fluss M. J.
Published: April 2011

We present results of molecular dynamics (MD) simulation studies of Cu segregation to the Σ11 grain boundary (GB) in Al. The simulations were performed with Embedded Atom Method (EAM) potentials for Al and Al-Cu. The results predict that copper atoms tend to order along either side of the interface even at the pure symmetrical GB, forming alternating chains along the direction. The nucleation of the chains is driven by a change in the local atomic level stress induced by the pre-existing Cu atoms at the GB.
In Situ Study of Al2Cu Precipitate Evolution During Zlectromigration in Submicron Al Interconnects
Authors: Theiss Silva K. , Prybyla J. A.
Published: April 2011

We have studied the behavior of Al2Cu precipitates during electromigration in submicron runners using in situ plan view TEM. Al (0.5 wt. % Cu) runners of widths between 0.3 and 1.0 μ were stressed at temperatures between 200 and 275° C and a current density of 2×106A/cm2. A greater number of precipitates nucleate per unit length in narrower runners (0.3 and 0.5 μ wide) than in wider runners (0.8 and 1.0 μ wide), although their average size is smaller in the narrower runners. The distribution of precipitates along the length of the runners is skewed towards the anode ends. Their number decreases and the skewing of their distribution increases with increasing temperature and linewidth. Precipitates are three times more likely to be found “downstream” (with respect to the electron flow) of a polygranular region and “upstream” of a blocking grain than the reverse. After their initial nucleation and growth, precipitates either decline in size or continue to grow during electromigration stressing depending on their position in the line and on the local grain structure. Grain boundaries profoundly influence the speed and direction of growth; however, the direction of growth cannot be predicted based on grain boundary inclinations alone. Precipitates tend to stay in one place and grow (or shrink) rather than migrate, in contrast to the behavior of voids which tend to migrate at higher temperatures. When precipitate migration occurs, it is either in association with void migration or by the replacement of small Al grains. Small precipitates remain compact as voids pass over or under them.
Electromigration in Single-Crystal Aluminum Lines Pre-Damaged by Nanoindentation
Authors: Joo Young-Chang , Baker Shefford P. , Knaufß Michael P. , Arzt Eduard
Published: April 2011

Electromigration tests have been performed on single-crystal Al lines which were predamaged by rows of submicrometer-depth indentations made using a nanoindentation device. Indentations were placed close to each other so that their plastic deformation zones overlapped. During subsequent electromigration testing at 280°C and I to 2 MA/cm2, no damage was observed in non-indented single-crystal lines, while the indented lines showed electromigrationinduced voids at the cathode-side ends of the indented areas, and hillocks at the anode-side ends. The voids grew and moved away from the indentations towards the cathode. Fhe electromigration damage morphology of the indented lines indicates that the mechanical damage generates a local fast diffusion path in the single-crystal lines, which is believed to be due to dislocation core diffusion. A minimum indentation row length was observed, below which no void formed. This electromigration behavior is found to be phenomenologically similar to that of polygranular clusters in near-bamboo lines.
Further Investigations of the Microstructural Mechanism of Electromigration Failure in Al-Cu Lines with Quasi-Bamboo Microstructures
Authors: Kang S. H. , Génin F. Y. , Kim C. , Morris J. W.
Published: April 2011

Thin-film Al-2Cu conducting lines with “quasi-bamboo” microstructures were investigated to understand the microstructural mechanism of electromigration failure. Both conventional test structures and electron-transparent lines fabricated on silicon nitride windows were utilized to identify the “weakest” polygranular segments. Even when the current density was reduced to 0.75 MA/cm2 and the segment length was on the order of a few microns, failure occurs at the upstream termination of the longest polygranular segment in the line, at a time that decreases exponentially with the segment length. There is no apparent “Blech length” in quasi-bamboo Al- Cu lines; the longest segments are the failure sites, and their lifetime decreases with segment length in a regular way, even when the longest segments are only a few microns in length. It follows (and is observed) that the time-to-failure distribution of a group of lines is fixed by the distribution of the longest polygranular segments within them. This distribution can be effectively controlled by post-pattern annealing, which can refine the quasi-bamboo structure so that the longest polygranular segments are short and the distribution of longest polygranular segment lengths is narrow. Consequently, post pattern annealing is a very effective method for improving reliability by increasing the time to first failure.
Accelerated Breakdown in Thin Oxide Films Due to Interfacial Stress and Carrier Depletion
Authors: Subramanian V. , Bhat N. , Saraswat K.
Published: April 2011

We present the results of experiments studying the effect of carrier depletion and interfacial stress on time to breakdown of'thin oxide films during constant current stressing High energy electrons resulting from carrier depletion conditions increase damage to oxides during tunneling. Carrier depletion conditions cause a dramatic decrease in time to breakdown and increase the number of early failures substantially. Mechanical interfacial stress results in a degradation in oxide reliability. Anode interfacial stress has been uniquely isolated from other phenomena such as cathode surface roughness, and has been shown to result in accelerated breakdown. These results have implications on oxide reliability and on test methodologies to obtain a measure of the same