bluuebunny/crossref_metadata_2025 huggingface dataset:
Copper Chalcopyrite Film Photocathodes for Direct Solar-Powered Water Splitting
Authors: Marsen Bjorn , Dorn Susanne , Cole Brian , Rocheleau Richard E. , Miller Eric L.
Published: April 2011

In search of an efficient semiconductor material for direct photoelectrochemical (PEC) hydrogen production, chalcopyrite films in the Cu(In,Ga)Se2system (CIGS) with bandgaps of 1.3-1.65 eV have been evaluated. The films have been fabricated by 2-stage and 3-stage co-evaporation processes. Film samples have been fabricated into CIGS/CdS solar cells for evaluation of solid-state device properties, and into CIGS photocathodes for evaluation of the photoelectrochemical hydrogen-production characteristics. The PEC current-potential scans of the photocathodes in 0.5M sulfuric acid show photocurrents of 18-27 mA/cm2under simulated AM1.5 global light (100 mA/cm2) at sufficient cathodic potential bias. In terms of fill factor of the photocurrent curves, electrodes with molybdenum back contact are superior to SnO2:F back contact because of better conductivity. The morphology as seen in scanning electron micrographs is unchanged after initial PEC testing in the cathodic regime, suggesting films are stable.
Conjugated Polymer-Based Flexible Photovoltaic Cells with Controlled Nanostructures
Authors: Kim Myung-Su , Kim Jin-Sung , Cho Jae Cheol , Shtein Max , Guo L. Jay , Kim Jinsang
Published: April 2011

We demonstrate that conjugated polymers (CPs)-based flexible solar cells with well-defined interdigitated donor-acceptor interfaces enhance charge separation and transport. The welldefined straight donor-acceptor interfaces are achieved successful application of nanoimprinting technology to rationally designed energy harvesting and hole transporting conjugated polymers. Nanoimprinting enables the precise and direct nano-scale control of the shape of the donoracceptor interface on both rigid and flexible substrates. Comparison between the performances of the solar cells having imprinted different feature sizes revealed that the short circuit current can be systematically increased by the interfacial area of the heterojunction without affecting the open circuit voltage. The results also showed that the vertically oriented heterojunction facilitate charge transport and allow synergistically improved fill factor, open circuit current, and ensuing energy conversion efficiency beyond the gain of the interfacial area of the heterojunction.
Electrical Response of Wet Chemically Grown ZnO Nanorods for Photovoltaic Application
Authors: Tornow Julian , Schwarzburg Klaus
Published: April 2011

Wet chemically prepared arrays of ZnO nanorods in electrolyte solution were investigated with respect to their capacitive behavior. The ZnO nanorod electrode could be well described by a frequency independent capacitive and a conductive element in parallel. The capacitive element is determined as space charge capacitance in the nanorods. However the dependency of the nanorod electrodes capacitance on the applied voltage bias is more complicated than for flat semiconductor electrodes.
Microcrystalline SiO and its Application to Solar Cell
Authors: Piromjit Channarong , Yotsaksri Decha , Pingate Nirut , Sichanugrist Porponth
Published: April 2011

As microcrystalline silicon oxide (μc-SiO) is reported to be more promising material than microcrystalline silicon carbide for the application to solar cells, both of high efficiency amorphous (top cell) and microcrystalline (bottom cell) silicon solar cells fabricated on tin oxide coated glass substrate have been developed by using μc-SiO p-layer and buffer i-layer. High VHF frequency of 60 MHz and carbon dioxide gas are used for their deposition. ZnO deposited by DC sputtering is coated on Asahi's type U tin oxide in order to promote the crystallization of the μc-SiO p-layer. It was found that the top cell with this novel mc-SiO p-layer has higher cell efficiency than the one with normal SiO p-layer. Furthermore, the microcrystalline bottom cell with novel μc-SiO p-layer and μc-SiO buffer layer has higher performance than the one with normal μc-Si p-layer. Up to now, an efficiency of more than 15% has been achieved with a-SiO/a-SiGe/μc-Si tandem cell.
Analytical TEM Observations of Au-Pd Nano-particles Prepared by Sonochemical Techniques
Authors: Akita Tomoki , Hiroki Taiei , Tanaka Shingo , Kojima Takao , Kohyama Masanori , Iwase Akihiro , Hori Fuminobu
Published: April 2011

The structure of Au-Pd bimetallic nanoparticles prepared by sonochemical technique was investigated by an analytical transmission electron microscopy. The core (Au)-shell (Pd) structure was clearly confirmed by the intensity profile of annular dark field scanning transmission electron microscopy (ADF-STEM). The line-scan analysis of energy dispersive X-ray spectroscopy (EDS) in STEM mode also revealed the Au core-Pd shell structure. The selected area electron diffraction pattern from the Au-Pd nanoparticles indicated the possibility that the crystal lattice of Pd shell is expanded and coincident with the crystal lattice of Au core.
Measurement of Moisture Migration Kinetics in Environmental Scanning Electron Microscopy
Authors: Tang Xiaohu , Rooij Mario de
Published: April 2011

Volume change of cereal materials caused by moisture migration is studied by Environmental Scanning Electron Microscopy (ESEM) using videomicroscopy and stereoscopy in combination with image processing. It is shown that the in situ volume change can be monitored by following the change of projection area, assuming isotropic volume change. Also the volume change measured by stereoscopy matches well with the measurement of the projection area change by videomicroscopy (after normalization). It is concluded that volume changes more in a higher relative humidity (RH) region with more active kinetic behavior. The exact volume change in between two relative humidities can be obtained by interpolating the equilibrium volumes. All the sorption/desorption curves can be well described by the ‘parallel exponential kinetics’ model (PEK model), which described two independent, parallel processes.
Electrical and Optical Modelling of Thin-Film Silicon Solar Cells
Authors: Zeman Miro , Krc Janez
Published: April 2011

Today amorphous and microcrystalline silicon based solar cells use surface-textured substrates for enhancing the light absorption and buffer and graded layers in order to improve the overall performance of the cells. Tandem and triple-junction configurations are utilized to assure better use of the solar spectrum and, thus, achieve higher conversion efficiencies of the devices. Resulting structures of the solar cells are complex and computer modeling has become an essential tool for a detailed understanding and further optimization of their optical and electrical behavior.

The performance limits of tandem and triple-junction silicon based solar cells are studied by simulations using the optical simulator SunShine developed at Ljubljana University and the opto-electrical simulator ASA developed at Delft University of Technology. First, both simulators were calibrated with realistic optical and electrical parameters. Then, they were used to study the required scattering properties, absorption in non-active layers, antireflective coatings, the crucial role of the wavelength selective intermediate reflector, and a careful current matching in order to indicate the way for achieving a high photocurrent, more than 15 mA/cm2 for a tandem a-Si:H/ìc-Si:H and 11 mA/cm2 for a triple-junction a-Si:H/a-SiGe:H/ìc-Si:H solar cells. By optimizing electrical properties of the layers and interfaces, for example using a p-doped a-SiC layer with a larger band gap (EG > 2 eV) and introducing buffer layers at p/i interfaces, the extraction of the charge carriers, the open-circuit voltage and the fill factor of the solar cells are improved. The potential for achieving the conversion efficiency over 15% for the a-Si:H/ìc-Si:H and 17 % for the triple-junction a-Si:H/a-SiGe:H/ìc-Si:H solar cells is demonstrated.
Comparative Study of Hot-Wire Chemical Vapor Deposition onto (100) Si Near 600°C: Epitaxial and Polycrystalline Silicon Films
Authors: Teplin Charles W. , Branz Howard M. , Jones Kim M. , To Bobby , Iwaniczko Eugene , Stradins Paul
Published: April 2011

Previously, we reported improved silicon epitaxy by hot-wire chemical vapor deposition (HWCVD) between about 600 and 650°C. Such temperatures are compatible with the thickening of large-grained Si seed layers on borosilicate glasses or other inexpensive substrates. Here, we provide detailed real-time spectroscopic ellipsometry (RTSE) and x-ray diffraction (XRD) analysis of two films grown near 600°C. A film grown at 594°C shows breakdown to a polycrystalline phase, while a film grown at 627°C is entirely epitaxial. Transmission electron microscopy (TEM) of this epitaxial film shows dislocation defects that originate at the substrate/film interface, suggesting that an optimized surface preparation could yield lower defect densities.
Microwave Activation of Dopants & Solid Phase Epitaxy in Silicon
Authors: Thompson Douglas C. , Decker J. , Alford T. L. , Mayer J. W. , Theodore N. David
Published: April 2011

Microwave heating is used to activate solid phase epitaxial re-growth of amorphous silicon layers on single crystal silicon substrates. Layers of single crystal silicon were made amorphous through ion implantation with varying doses of boron or arsenic. Microwave processing occurred inside a 2.45 GHz, 1300 W cavity applicator microwave system for time-durations of 1-120 minutes. Sample temperatures were monitored using optical pyrometery. Rutherford backscattering spectrometry, and cross-sectional transmission electron microscopy were used to monitor crystalline quality in as-implanted and annealed samples. Sheet resistance readings show dopant activation occurring in both boron and arsenic implanted samples. In samples with large doses of arsenic, the defects resulting from vacancies and/or micro cluster precipitates are seen in transmission electron micrographs. Materials properties are used to explain microwave heating of silicon and demonstrate that the damage created in the implantation process serves to enhance microwave absorption.
Optimisation of Microcrystaline Silicon Deposited by Expanding Thermal Plasma Chemical Vapor Deposition for Solar-Cell Application
Authors: Jimenez Zambrano Raul , van Swaaij R.A.C.M.M. , van de Sanden M.C.M.
Published: April 2011

The causes for the porosity of the microcrystalline material deposited by the expanding thermal plasma (ETP) chemical vapor deposition (CVD) technique have been investigated through IR-absorption measurements. The role of impinging ions on the structure of the material is discussed in relation to the hydrogen bounding configuration (microcrystalline factor). The ion energy is controlled through external RF biasing. Correlation between biasing and reduction of porosity is presented. The influence of high deposition pressure is as well studied, related with changes in a-Si structure.
Phase Control and Stability of Thin Silicon Films Deposited from Silane Diluted with Hydrogen
Authors: van Elzakker Gijs , Šutta Pavol , Tichelaar Frans D. , Zeman Miro
Published: April 2011

Hydrogen dilution of silane during the rf-PECVD growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. The increased stability of cells and films deposited using hydrogen dilution is verified in an accelerated degradation experiment. At higher hydrogen dilutions the early phase transition to the microcrystalline phase complicates the growth of fully amorphous films as absorbers with a sufficient thickness. In a systematic study on the influence of various deposition conditions on the material properties the pressure is identified as an important factor for controlling the structural phase evolution of the films.
High Mobility Nanocrystalline Silicon TFTs for Display Application
Authors: Han Min-Koo , Han Sang-Myeon
Published: April 2011

Nanocrystalline silicon (nc-Si) thin film transistors (TFTs) of which active layer thickness was 100nm were fabricated using inductively coupled plasma chemical vapor deposition (ICP-CVD) at 150°C. The fabricated nc-Si TFT exhibits rather high field effect mobility exceeding 22cm2/Vs and excellent sub-threshold slope of 0.45V/dec. The nc-Si film deposited 150°C as an active layer of the TFT shows high crystallinity more than 70% and very thin incubation layer less than 20nm. ICP-CVD provides high density plasma with reduced ion bombardment during the deposition on nc-Si and He dilution can enhance the decomposition of SiH4 into Si, SiHX radicals and atomic H, so that high quality nc-Si film can be fabricated. The gate insulator SiO2 film deposited by ICP-CVD at 150°C shows good electrical characteristics such as flat band voltage of -1.8V and breakdown voltage of 6.2MV/cm.
Pecvd Grown p-i-n Si and Si,Ge Thin Film Photodetectors For Integrated Oxygen Sensors
Authors: Ghosh Debju , Shinar Ruth , Dalal Vikram L. , Zhou Zhaoqun , Shinar Joseph
Published: April 2011

Recent efforts to advance photoluminescence (PL)-based oxygen sensors have focused on developing compact, field-deployable devices. This has led to organic light emitting device (OLED)-based sensors with a structurally integrated [OLED excitation source]/[sensing film] module. To additionally integrate a photodetector (PD), PECVD for fabrication of thin-film p-i-n and n-i-p Si- and Si,Ge-based PDs was employed. O2 concentrations are advantageously determined by monitoring the effect of O2 on shortening the PL decay time  of an oxygen-sensitive dye, rather than on quenching its PL intensity. This approach, which employs pulsed OLEDs, eliminates the need for frequent sensor calibration, minimizes issues associated with background light, and eliminates the need for optical filters, which lead to bulkier sensors. However, it requires PDs with response times significantly shorter than . Therefore, the development of thin-film PDs focused on decreasing their response time, and understanding the factors affecting it. In this paper we show that boron diffusion during growth from the p+ to the i layer increases the response time of PECVD grown p-i-n PDs. Incorporating a SiC buffer layer and fabricating superstrate structures, where the p+ layer is grown last, decrease it. Additionally, ECR fabricated PDs show a slower response in comparison to VHF PECVD-grown PDs.
Modeling and Characterization of the Hydrogenated Amorphous Silicon Metal Insulator Semiconductor Photosensors for Digital Radiography
Authors: Safavian Nader , Vygranenko Y. , Chang J. , Kim Kyung Ho , Lai J. , Striakhilev D. , Nathan A. , Heiler G. , Tredwell T. , Fernandes M.
Published: April 2011

Because of the inherent desired material and technological attributes such as low temperature deposition and high uniformity over large area, the amorphous silicon (a-Si:H) technology has been extended to digital X-ray diagnostic imaging applications. This paper reports on design, fabrication, and characterization of a MIS-type photosensor that is fully process-compatible with the active matrix a-Si:H TFT backplane. We discuss the device operating principles, along with measurement results of the transient dark current, linearity and spectral response.
Comparative Study of Solid-Phase Crystallization of Amorphous Silicon Deposited by Hot-wire CVD, Plasma-Enhanced CVD, and Electron-Beam Evaporation
Authors: Stradins Paul , Kunz Oliver , Young David L. , Yan Yanfa , Jones Kim M. , Xu Yueqin , Reedy Robert C. , Branz Howard M. , Aberle Armin G. , Wang Qi
Published: April 2011

Solid-phase crystallization (SPC) rates are compared in amorphous silicon films prepared by three different methods: hot-wire chemical vapor deposition (HWCVD), plasma-enhanced chemical vapor deposition (PECVD), and electron-beam physical vapor deposition (e-beam). Random SPC proceeds approximately 5 and 13 times slower in PECVD and e-beam films, respectively, as compared to HWCVD films. Doping accelerates random SPC in e-beam films but has little effect on the SPC rate of HWCVD films. In contrast, the crystalline growth front in solid-phase epitaxy experiments propagates at similar speed in HWCVD, PECVD, and e-beam amorphous Si films. This strongly suggests that the observed large differences in random SPC rates originate from different nucleation rates in these materials while the grain growth rates are relatively similar. The larger grain sizes observed for films that exhibit slower random SPC support this suggestion.
Elastic Properties of Several Silicon Nitride Films
Authors: Liu Xiao , Metcalf Thomas H , Wang Qi , Photiadis Douglas M
Published: April 2011

We have measured the internal friction (Q-1) of amorphous silicon nitride (a-Si3Nx) films prepared by a variety of methods, including low-pressure chemical-vapor deposition (LPCVD), plasma-enhanced chemical-vapor deposition (PECVD), and hot-wire chemical-vapor deposition (HWCVD) from 0.5 K to room temperature. The measurements are made by depositing the films onto extremely high-Q silicon double paddle oscillator substrates with a resonant frequency of ~5500 Hz. We find the elastic properties of these a-Si3N4 films resemble those of amorphous silicon (a-Si), demonstrating considerable variation, depending on the film growth methods and post deposition annealing. The internal friction for most of the films shows a broad temperature-independent plateau below 30 K, characteristic of amorphous solids. The values of Q-1, however, vary from film to film in this plateau region by more than one order of magnitude. This is typical for tetrehedrally bonded amorphous thin films, like a-Si, a-Ge, and a-C. The PECVD films have the highest Q-1 just like an ordinary amorphous solid, while LPCVD films have an internal friction more than one order of magnitude lower. All the films show a reduction of Q-1 after annealing at 800°C, even for the LPCVD films which were prepared at 850°C. This can be viewed as a reduction of structural disorder.
Recent Progress in Up-Scaling of Amorphous and Micromorph Thin Film Silicon Solar Cells to 1.4 m2 Modules
Authors: Meier Johannes , Kroll Ulrich , Benagli Stefano , Roschek Tobias , Huegli Andreas , Spitznagel Joel , Kluth Oliver , Borello Daniel , Mohr Michael , Zimin Dmitri , Monteduro Giovanni , Springer Jiri , Ellert Christoph , Androutsopoulos Girogios , Buechel Gerold , Zindel Arno , Baumgartner Franz , Koch-Ospelt Detlev
Published: April 2011

In this paper an overview of our developments towards industrialization of thin film silicon PV modules is presented. Amorphous silicon p-i-n solar cells have been developed in medium size single-chamber R&D KAI-M PECVD reactors. High initial efficiencies of 10.6 % and stabilized of 8.6 % could be achieved for a 1 cm2 a-Si:H p-i-n solar cell of 0.20 m thick i-layer deposited on TCO from Asahi U type (SnO2). On our in-house developed LPCVD ZnO we could further improve the stabilized a-Si:H p-i-n efficiency to a similar level of 8.5 %. Incorporating such cells in commercial available front TCO of lower quality still leads to high initial mini-module aperture efficiencies (10 × 10 cm2) of 9.1% and stabilized ones of 7.46% (independently measured by ESTI JRC-Ispra).

Transferring the processes from the KAI-M to the industrial size 1.1×1.25 m2 KAI-1200 R&D reactors resulted in a-Si:H modules of 110.6 W using commercial TCO, respectively 112.4 W when applying in-house developed LPCVD front ZnO. Both initial module performances have been independently measured by ESTI laboratories of JRC Ispra. A typical temperature coefficient for the module power of -0.22 %/°C (relative loss) has been deduced from temperature dependent I-V characteristics at ESTI laboratories of JRC Ispra. Finally, micromorph mini-modules of 10 % initial aperture efficiency have been fabricated.
Time-resolved Cavity Ringdown Spectroscopy as a Monitoring Technique of Nanoparticles in Pulsed VHF Plasmas
Authors: Nagai Takehiko , Smets Arno H. M. , Kondo Michio
Published: April 2011

Time-resolved cavity ringdown (τ-CRD) spectroscopy has been applied to monitor the sylil (SiH3) radicals and nano-particles in pulsed very high frequency (VHF) silane (SiH4)/hydrogen (H2) plasmas under microcrystalline silicon (μc-Si:H) deposition conditions. After the plasma ignition, a small constant cavity loss (~100 ppm) on timescales smaller than ~1 s has been observed, whereas on time scales larger than ~1 s after plasma ignition, an additional cavity loss is observed. By variation of the wavelength of the CRD laser pulse, we demonstrate that the cavity loss on time scales smaller than ~1 s reflects the SiH3 absorption. On time scales larger than ~1 s, the additional cavity loss corresponds to the loss of light due to mainly scattering at the nano-particles. Under the conditions studied, the light scattering at nano-particles can be described by Rayleigh scattering during its initial growth. After ~ 2.5 s, the cavity loss reflects the transition of the scattering mechanism from dominant Rayleigh to dominant Mie-scattering. These results are discussed in terms of nano-particles growing in time and further confirmed by additional scanning electron microscopy analyses on the nano-particles created in the plasma pulse.
Advances in Understanding and Control of CMP Performance: Contact-Hydrodynamics at Wafer, Groove, and Asperity Scale
Authors: Muldowney Gregory P.
Published: April 2011

Examining CMP at any scale, one finds coupled contact mechanics and fluid mechanics. Increasingly sophisticated experimental and computational techniques have revealed aspects of solid-solid interaction and slurry flow at the wafer and groove scale and, more recently, at the texture scale. Successful prediction of CMP performance hinges on identifying universal physics that span these scales. In this paper we first review results of novel asperity-scale experiments that characterize the pad texture both as a solid topography subject to contact deformation and as an equivalent porous medium for slurry flow. These measures reveal that much of the texture volume is inactive as flow space, a feature confirmed quantitatively by computational modeling of flow across a conditioned CMP pad surface built from 3-D microscopy images. For hydrodynamics, the findings establish active fluid volume per unit area as the property that bridges from asperity scale to wafer scale. We then derive a fundamental basis for CMP removal rate prediction based on contact and hydrodynamics, using a Sommerfeld number defined across the groove and texture length scales. The resulting equation, containing a single unknown proportionality constant, demonstrates that the often used product of downforce and table speed tracks removal rate only when the hydrodynamic state affords adequate pad-wafer contact. Departures from the Preston equation attributed in other models to chemically-limited regimes of CMP are explained in the present treatment as changes in hydrodynamic film thickness and contact area—a fact confirmed by direct measurement. Removal rate predictions are discussed for ILD, STI, and copper processes using both conventional and non-Prestonian slurries, including variations in downforce, table speed, temperature, pad properties, and groove design. Finally, the influence of regional pad-wafer hydrodynamics is illustrated by applying the contact-hydrodynamics equation to grooves specially configured to vary the slurry film thickness from wafer center to edge. Local removal rates are well predicted using locally defined values of the groove-texture Sommerfeld number, confirming the generality of the contact-hydrodynamic description at least from wafer to asperity scale. Findings are further discussed in the context of next-generation pad architectures—not only to achieve more effective pad-wafer contact and slurry delivery, but also to favorably decouple contact and fluid mechanics in CMP pad design.
Surfactants in Controlling Removal Rates and Selectivity in Barrier Slurry for Cu CMP
Authors: Bian Jinru
Published: April 2011

Leading edge integrated circuits (ICs) are complicated structures designed to have up to 3 capping layers above a low k dielectric material. The upper capping layer may use TEOS and/or silicon nitride (SiN), while the lower one may use silicon carbon nitride (SiCN), silicon carbide (SiC), or carbon doped oxide (CDO) immediately above the low k dielectric. Therefore, a barrier slurry for copper CMP, in addition to exhibiting a high removal rate of the barrier, must be able to remove the upper capping layer and stop at the underlying dielectric surface.

We have developed a slurry family that can effectively remove TaN, TEOS, SiN, CDO, and/or SiCN, or any combination of these films, or can stop at any one or two film surfaces of TEOS, SiN, CDO, SiCN, and SiC, depending on the specific slurry design. Removal rate control is achieved by one or two additives. One of the additives is an anionic surfactant. When selecting a surfactant, the surfactant hydrophobicity and charge interaction between the surfactant and the wafer surface are two important factors to be considered. This report discusses these two factors in selecting a proper surfactant for a specific slurry application.
Defect Structures of B12As2 Epilayers Grown on c-plane and a-plane 6H-SiC Substrates
Authors: Chen Hui , Wang Guan , Dudley Michael , Zhang Lihua , Zhu Yimei , Zhang Yi , Edgar James H. , Kuball Martin
Published: April 2011

B12As2 epitaxial layers grown on (0001) 6H-SiC and (1120) 6H-SiC substrates have been studied using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and synchrotron white beam x-ray topography (SWBXT) and investigated with the aid of crystal visualization software. SWBXT showed that B12As2 adopted [111] growth orientation, parallel to [0001]SiC, on c-plane 6H-SiC and adopted [101] growth orientation, parallel to [1120]SiC, on a-plane 6H-SiC. However, SWBXT also revealed the twins in both sets of the B12As2 films, consistent with the SEM observation of the surface morphology. Cross-sectional HRTEM also confirmed the presence of twins in both cases and also revealed the existence of an intermediate layer between the c-plane 6H-SiC and the B12As2 film. By correlating the HRTEM observation and crystal visualization, the atomic configurations across the twin boundaries in both samples as well as those in the intermediate layer in the c-plane sample were proposed.
Lead Iodide Thin Films Grown Using N.N-Dimethylformamide as Solvent
Authors: Fernando Condeles Jose , Caldeira-Filho Ademar Marques , Mulato Marcelo
Published: April 2011

Spray pyrolysis was used for the deposition of lead iodide (PbI2) thin films using N.N-dimethylformamide (DMF) as an alternative solvent under varying deposition parameters. Final thickness of 60 μm was obtained for a total deposition time of 2.5 hours. The films were characterized mainly by using Raman and photoluminescence, but additional techniques such as X-ray diffraction, scanning electron microscopy and dark conductivity as a function of temperature were also employed. Thick PbI2 films deposited by spray pyrolysis using DMF as a solvent are promising to be used in medical systems as X-ray imaging.
Comparison of Silicon Photoluminescence and Photoconductive Decay for Material Quality Characterization
Authors: Johnston Steven , Ahrenkiel Richard , Dippo Pat , Page Matt , Metzger Wyatt
Published: April 2011

Minority-carrier lifetime in silicon directly relates to defect- and impurity-related recombination, and thus gives a measure of material quality. Lifetime measurements are useful in research laboratories and commercial production environments as an indicator for process development and quality control. While photoconductivity (PCD) techniques for measuring lifetime are commercially available, there has recently been interest in using photoluminescence (PL) to characterize lifetime in silicon because of the measurement speed to image an entire wafer and higher mapping resolution. The intensity of band-to-band PL is theoretically proportional to the effective bulk lifetime in low-injection conditions if carrier diffusion and re-absorption are neglected, surface recombination is small, and silicon properties, such as carrier concentration and the radiative recombination coefficient, are constant. We show data that compare lifetimes from PCD techniques to PL intensity for varying-resistivity, single-crystal silicon. Surface conditions are also varied (native oxide, thermal oxide, and HF etch/methyl-iodine solution), and the measured lifetimes are compared to corresponding PL intensity.
Characterization of the Segregation of Arsenic at the Interface SiO2/Si
Authors: Steen Christian , Pichler Peter , Ryssel Heiner , Pei Lirong , Duscher Gerd , Werner Matt , van den Berg Jaap A. , Windl Wolfgang
Published: April 2011

The segregation of As atoms at the Si/SiO2 interface during annealing was investigated by grazing incidence X-ray fluorescence spectroscopy in combination with successive removal of silicon layers by etching with thicknesses on the order of a nanometer. With this method it is possible to clearly distinguish between the segregated atoms and the As atoms in the bulk over a large range of implantation doses from 3·12 cm−2 to 1·16 cm−2. The samples were annealed at 900 °C and 1000 °C, respectively, for times sufficiently long to ensure that the segregation reflects an equilibrium effect. The results were confirmed by medium energy ion scattering, Z-contrast measurements and electron energy loss spectroscopy.
An Experimental and Simulation Study of Arsenic Diffusion Behavior in Point Defect Engineered Silicon
Authors: Kong Ning , Kirichenko Taras A. , Hwang Gyeong S. , Mark Foisy C. , Anderson Steven G. H. , Banerjee Sanjay K.
Published: April 2011

We report that arsenic diffusion can be enhanced and retarded by surrounding interstitial rich and vacancy rich environments created by Si point defect engineering implant. The enhancement and retardation can be attributed to the dominant arsenic interstitial diffusion mechanism during post-implant anneal. Kinetic Monte Carlo simulations with newly implemented models show good match with experiments. Our study suggests the importance of arsenic interstitial mechanism and a possible approach for n-type ultra shallow junction fabrication.
Silver Nanocrystals at Cavities Created by High Energy Helium Implantation in Bulk Silicon
Authors: El Bouayadi Rachid , Regula Gabrielle , Lancin Maryse , Larios Eduardo , Pichaud Bernard , Ntsoenzok Esidor
Published: April 2011

High resolution transmission electron microscopy observations show for the first time the presence of two orientations of pure silver precipitates in nanocavities induced in bulk silicon by implantation at 1.6 MeV with a dose of 5×1016 He+ cm−2 and a two hour annealing at 1050°C. These precipitates were called A and B to refer to the two well-known nickel silicide (NiSi2) precipitates or Ag films on a {111} silicon surface. Thus, the A precipitate corresponds to a growth of silver nanocrystal on {111} cavity walls in epitaxy with the Si matrix with an orientation relationship Ag(-111)[211]||Si(-111)[211]. The B precipitate develops on a {111} plane parallel to a {111} cavity wall as well, but in a twin orientation with respect to the Si matrix defined by Ag(-111)[211]||Si(-111)[-2-1-1]. The Ag nanocrystals have a size ranging from a few nm to 50 nm. Most of them have the faceted-shape characteristic of “clean” cavities. They are either A precipitates or they contain alternatively A and B bands in good agreement with both the low stacking fault energy of silver and the two types of nanocrystal orientations obtained by Ag deposition on (111) Si substrate at room temperature. Some Ag precipitates were also found at dislocations located at the He+ projection range, but these trapping sites were found thermally unstable as compared to the cavity ones. Indeed, during a second identical annealing, the precipitates grow in cavities whereas they fade at dislocations.
Microwave Activation of Exfoliation in Ion–cut Silicon Layer Transfer
Authors: Thompson Douglas C. , Alford T. L. , Mayer J. W. , Hochbauer T. , Lee J. K. , Nastasi M. , Theodore N. David
Published: April 2011

Microwave heating is used to initiate the ion-cut process for transfer of coherent silicon-layers onto insulator substrates. Hydrogen and boron co-implanted silicon was bonded to an insulative substrate before processing inside a 2.45 GHz, 1300 W cavity applicator microwave system. Sample temperatures measured using a pyrometer were comparable to previous ion – cut studies. Selected samples were further annealed to repair any damage created in the ion implant process. Rutherford backscattering spectrometry and selective area electron diffraction patterns show high crystallinity in transferred layers. RUMP simulation of backscattering spectra and cross-sectional transmission electron microscopy demonstrate that thicknesses of the transferred layers are comparable to previous ion-cut exfoliation techniques. Surface quality as characterized by an atomic force microscope compares well with previous ion-cut studies. Hall measurements were used to characterize electrical properties of transferred layers. The mobility and carrier density of microwave activated ion – cut silicon on insulator processed samples compares well with previous annealing techniques.
The Charge Carriers Transport Mechanism Through the Interface Layer of the p-GaSe(Cu)/n+GaAs Heterojunctions
Authors: Cuculescu Elmira I. , Caraman Mihail I.
Published: April 2011

The photoelectrical properties of p-GaSe(Cu)/n-GaAs heterojunctions obtained by optically contacting the components and by thermal evaporation of GaSe, have been studied. The rectification factor for optically contacted heterojunctions is ∼2·102 at 5 V, and the current flow is determined by diffusion mechanism. The diffusion and recombination through the interface defects mechanisms determine de current flow for heterojunctions formed by GaSe evaporation.
Design and Simulation of High Efficiency Silicon Light-Emitting Diodes
Authors: Pan Grant Z. , Peretzman Jaime , Pak Dae H. , Ren Li P.
Published: April 2011

Four boron-implanted p-n junction silicon light-emitting diode structures were designed and simulated under an identical process flow by using Silvaco simulators. In the simulation, only boron-implant parameters and post-implant anneal conditions were varied to identify and compare the physical, electrical, and optical properties of the structures. It was found that a pillar structure with a wrapped p-n junction has the greatest radiative recombination rate. Regardless the structure type, the maximum radiative recombination rate always occurs within the p+ region. There exists a peak in the maximum radiative recombination rate when the anneal temperature increases from 700 to 1100 °C, and the anneal temperature at peak increases while the implant dose increases. Furthermore, the radiative recombination rate always increases with the implant dose but it saturates at a high dose. However, the radiative recombination rate does not change significantly with the implant energy.
Bright-Pixel Defects in Irradiated CCD Image Sensors
Authors: McColgin William C , Tivarus Cristian , Swanson Craig C. , Filo Albert J.
Published: April 2011

We have examined environmental radiation sources for digital cameras to find the origins of bright-pixel defects known to accumulate with time. We show that beta and gamma emissions from camera parts and lenses cause image transients, but permanent damage can occur with alpha particles from the CCD cover glass. Our experiments with 14-MeV- and thermal-neutron beams confirm that cosmic rays are the primary cause of new imager bright points.
Strain-Transfer Structure Beneath the Transistor Channel for Increasing the Strain Effects of Lattice-Mismatched Source and Drain Stressors
Authors: Yeo Yee-Chia , Ang Kah-Wee , Lin Jianqiang , Lam Chee-Shing
Published: April 2011

We incorporate an additional semiconductor heterostructure beneath the transistor channel region to increase the strain-transfer efficiency of lattice-mismatched source/drain (S/D) stressors, resulting in higher strain levels in the channel region. The additional structure is lattice-mismatched with respect to the overlying Si-channel and/or with respect to the S/D stressors. For an n-FET with Si:C S/D, a SiGe region integrated beneath the Si-channel enhances the magnitude of the tensile strain in the channel region. For a p-FET with SiGe S/D, a Si:C region beneath the Si-channel enhances the strain effect in the channel region. This additional structure beneath the transistor channel is called a strain-transfer structure (STS). Extensive numerical simulations were performed using the finite element method to explain how the new strain-transfer structure works. Profiles of the various strain components in the transistor channel were obtained. Dependence of the strain effect on geometrical features of the new transistor structure will also be reported.
Nucleation Studies of HfO2 Thin Films Produced by Atomic Layer Deposition
Authors: Hackley Justin C. , Demaree J. Derek , Gougousi Theodosia
Published: April 2011

A hot wall Atomic Layer Deposition (ALD) flow reactor equipped with a Quartz Crystal Microbalance (QCM) has been used for the deposition of HfO2 thin films with tetrakis (dimethylamino) hafnium (TDMAH) and H2O as precursors. HfO2 films were deposited on H-terminated Si and SC1 chemical oxide starting surfaces. Spectroscopic ellipsometry (SE) and QCM measurements confirm linear growth of the films at a substrate temperature of 275°C. FTIR spectra indicate the films are amorphous as-deposited. Two distinct growth regimes are observed: from 1-50 cycles, both surfaces display similar growth rates of about 1.0Å/cycle; from 50-200 cycles, HfO2 growth is decreased by about 15% to ~0.87Å/cycle on both surfaces. Nucleation and initial growth behavior of the films on Si-H were examined using X-ray photoelectron spectroscopy (XPS). Angle-resolved XPS, at take-off angles of θ=0, 15, 30, 45 and 60° measured from the normal to the sample surface, is used to probe the interfacial region of thin films (4, 7, 10, 15 and 25 cycles) on H-terminated samples. Initially, an interfacial layer comprised of a SiOx/HfSiOx mixture is grown between 1-10 ALD cycles. We observe that the Si/HfO2 interface is unstable, and oxidation continues up to the 25th ALD cycle, reaching a thickness of ~18Å.
A New 3D Multistring Code to Identify Compound Oxide Nanophase With Ion Channeling
Authors: Bradley James Douglas , Herbots Nicole , Culbertson Robert , Shaw Justin , Atluri Vasu
Published: April 2011

A new 3DMultiString computer code of Ion Beam Analysis (IBA) using 4He++ ion channeling combined with Nuclear Resonance Analysis (NRA) is used to analyze controlled formation of order in continuous layers of silicon dioxide nucleated on (1×1) Si(100) via the Herbots-Atluri clean (U.S. patent 6,613,677 (9/3/2003)) in air at 300 K. In our most recent work, this new 3DMultiString simulations combined with IBA leads to the identification of a new two-dimensional nanophase of tetragonally distorted β-cristobalite SiO2 (annotated b-c SiO2) with a critical thickness of 2 nm from the (1×1) Si (100)/b-c SiO2 interface to the b-c SiO2 /amorphous SiO2 interface (annotated b-c SiO2/a-SiO2). 3DMultiString simulations of IBA data taken on this new b-c SiO2/(1×1) Si(100) interphase includes channeling along the three <100>, <110>, and <111> axes of Si (100) in combination 16OO(α, α)16O 3.045 MeV NRA to measure oxygen areal densities corresponding to nm-thick films. In this way, the critical thickness of the β-c SiO2 nanophase can be established as a function of oxygen coverage. This new 3DMultiSTRING computer code is derived from the original 3DSTRING program that originated at Bell Labs, NJ.
Electrical Characterization of High-k Dielectrics by Means of Flat-Band Voltage Transient Recording
Authors: Duenas Salvador , Castán Helena , García Héctor , Bailón Luis , Kukli Kaupo , Ritala Mikko , Leskela Markus
Published: April 2011

We have carried out a comparison between flat-band transients displayed in metal-oxide-semiconductor (MOS) structures fabricated on several atomic layer deposited (ALD) high-k dielectric films: HfO2, ZrO2, Al2O3, Ta2O5, TiO2, and Gd2O3. The gate voltage as a function of time is recorded while keeping constant the capacitance at the initial flat band condition (CFB). Since samples are in darkness, under no electric fields and no charge-injection conditions, transients must be due to charge trapping of localized states produced by electrons (holes) coming from the semiconductor by tunnelling. The process is assisted by phonons and it is therefore thermally activated. The temperature-transient amplitude relation follows an Arrhenius plot which provides the thermal activation energy of soft-optical phonons. Finally, we describe the dependencies of the flat-band voltage on the setup bias history (accumulation or inversion) and the hysteresis sign (clockwise or counter-clockwise) of the capacitance-voltage (C-V) characteristics of MOS structures.
The Fine Structure of the Mn Distribution in ZnO Layers Deposited by Magnetron Sputtering for Spintronic Application
Authors: Abouzaid Morad , Ruterana Pierre
Published: April 2011

In this work, we carry out structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering, using transmission electron microscopy (TEM) and high resolution x-ray diffraction. On top of sapphire (0001) substrates, Mn rich precipitates and an interface reaction layer are observed following the deposition of Zn(Mn)O layers above 500°C. The crystalline quality of ZnO layers deposited by magnetron sputtering is highly improved at 500°C as well as the measured ferromagnetic response.
Micro/Nanofabrication by Spin Dewetting on a Poly(Dimethylsiloxane) Mold
Authors: Ferrell Nicholas , Bross Aimee , Hansford Derek
Published: April 2011

The process of spin dewetting was used to fabricate polymer micro and nanostructures from poly(methyl methacrylate) (PMMA), poly (propyl methacrylate) (PPMA), and polystyrene (PS). Polymer structures were formed on poly(dimethylsiloxane) (PDMS) molds by dewetting of a polymer solution during spin coating. Features were removed from the mold using heat and pressure to transfer the polymer to silicon or glass substrates. By varying the coating conditions, a variety of different polymer feature morphologies were obtained for a given PDMS mold geometry. In this study, the ability to fabrication polymer micro and nanostructures using spin dewetting was demonstrated on a variety of PDMS mold geometries. The effects of polymer solution concentration and mold feature size on the resulting polymer structures were examined. In addition, microfabricated PMMA structures were used as etch masks for anisotropic etching of silicon in an aqueous solution of tetramethylammonium hydroxide (TMAH).
Modeling of Self-Assembly Dynamics of Photolithographically Patterned MUFFINS Biosensor Arrays
Authors: Lee Saul , Carmichael Peter , Meiring Jason , Dickey Michael , Grayson Scott , Bonnecaze Roger T. , Willson C. Grant
Published: April 2011

The ability to mass produce biosensor arrays at low costs is an important target for the diagnostics industry. Our group has previously explored the batch production of mesoscale sized hydrogels as platforms for biosensors using photolithographic techniques. The individual hydrogel features were self-assembled through lateral capillary interactions to form a closed packed configuration and the pre-polymer medium was subsequently UV-cured to form the array. To understand the self-assembly dynamics, we investigated, through simulation, the flotation behavior of two assembling particles and its dependence on physical constants such as surface tension and particle density. Simulation results revealed that the objects tilt toward each other as they came into proximity. The tilt angle decreased with increasing surface tension but increased with increasing particle density. Understanding the details of the flotation behavior is necessary in the development of a full scale self-assembly model.
In-plane Molecular Alignment in Thin Films of Pentacene Grown by Solution Casting and Performance of Thin Film Transistors
Authors: Minakata Takashi , Nastume Yutaka
Published: April 2011

We have fabricated solution-processed thin films of pentacene by casting solution on a substrate and vaporizing solvent. The films with large oriented platelet domains were obtained by directionally grown condition. Molecular alignment in the directionally grown grains has been studied by several kinds of structural analysis. Oriented domains with the width of several hundreds microns and the length in an order of cm of the films were confirmed by polarized microscopy. In-plane crystalline structure of the domain has been studied by grazing incidence X-ray diffraction (GIXD) and strong anisotropy of in-plane crystalline structure was confirmed. Crystalline growth direction of the film was determined to be b-axis from both transmission electron diffraction and GIXD. Thin films transistors (TFTs) with directionally oriented domains of the films were fabricated on electrode patterned substrate. The observed maximum carrier mobility of 2.7 cm2/Vs was comparable to that of single crystal, which indicated that the quality of the film was almost identical with the single crystal. Correlation between FET performance and growth direction was studied and preferred performance of TFTs with the film grown perpendicularly to the channel was observed.
Fast Photoresponse of Functionalized Pentacene and Anthradithiophene Thin Films
Authors: Day Jonathan , Ostroverkhova Oksana , Anthony John
Published: April 2011

We present photoconductivity of high-performance functionalized pentacene and anthradithiophene thin films on time scales from picoseconds to many seconds after photoexcitation. The polycrystalline thin films were deposited from solution on glass substrates with patterned interdigitated aluminum electrodes. In studies of fast transient photoconductivity, the samples were excited with laser pulses of ~100 fs duration at a wavelength of 400 nm, and the photocurrent due to transport of photoexcited charge carriers was monitored using 50 GHz digital sampling oscilloscope. The photoconductivity at longer (milliseconds through seconds) time scales was investigated using continuous wave (cw) illumination and a source-delay-measure unit. Both experiments were performed under conditions of varied electric field strength, fluence and temperature. In all samples, we observed fast charge carrier photogeneration (<30 ps, limited by time resolution of our setup) followed by decay of the photocurrent over the period of 5-50 ns, depending on the material, due to charge trapping and recombination, linear dependence of the peak photoconductivity on the fluence and super-linear dependence of the peak photocurrent on the applied electric field.
A Planar Electroosmotic Micropump for Lab-on-Microchip Applications
Authors: Seibel Konstantin , Schöler Lars , Schäfer Heiko , Walder Marcus , Böhm Markus
Published: April 2011

The scope of the paper is to provide a theoretical and experimental treatment allowing to optimize critical design parameters for planar electroosmotic micropumps. The suggested design with a vertical arrangement of multiple narrow polymer pumping microchannels reduces the pump area to 1/10 compared to planar micropumps with widened shallow pumping channels. This design allows the fabrication of the channel system in only one process step, compatible with post-CMOS processing and suitable for monolithical integration on labchips. A simple analytical model has been developed to characterize the flow rate in a field free pressure-driven section of the channel. It is shown that the micropump with optimized dimensions of rib structures makes possible high pressure low voltage pumping. For high pressure capacity the distance between the ribs must be on the order of 0.5-1 µm with an aspect ratio of 10-20. The electroosmotic micropump with microchannels of SU-8 and polyacrylamide gel electrodes has been fabricated and tested. The pumping rate is bidirectionally linear and reached 10 nl/min at applied voltage of 40 V in 1 cm long pressure-driven channel, which corresponds to zero-flow pressure of 65 Pa.