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Rapid thermal annealing by, e.g., laser scanning of hydrogenated amorphous silicon (a-Si:H) films is of interest for device improvement and for development of new device structures for solar cell and large area display application. For well controlled annealing of such multilayers, precise knowledge of temperature and/or hydrogen diffusion length in the heated material is required but unavailable so far. In this study, we explore the use of deuterium (D) and hydrogen (H) interdiffusion during laser scanning (employing a continuous wave laser at 532 nm wavelength) to characterize both quantities. The evaluation of temperature from hydrogen diffusion data requires knowledge of the high temperature (T > 500 °C) deuterium-hydrogen (D-H) interdiffusion Arrhenius parameters for which, however, no experimental data exist. Using data based on recent model considerations, we find for laser scanning of single films on glass substrates a broad scale agreement with experimental temperature data obtained by measuring the silicon melting point and with calculated data using a physical model as well as published work. Since D-H interdiffusion measures hydrogen diffusion length and temperature within the silicon films by a memory effect, the method is capable of determining both quantities precisely also in multilayer structures, as is demonstrated for films underneath metal contacts. Several applications are discussed. Employing literature data of laser-induced temperature rise, laser scanning is used to measure the H diffusion coefficient at T > 500 °C in a-Si:H. The model-based high temperature hydrogen diffusion parameters are confirmed with important implications for the understanding of hydrogen diffusion in the amorphous silicon material.Rapid thermal annealing by, e.g., laser scanning of hydrogenated amorphous silicon (a-Si:H) films is of interest for device improvement and for development of new device structures for solar cell and large area display application. For well controlled annealing of such multilayers, precise knowledge of temperature and/or hydrogen diffusion length in the heated material is required but unavailable so far. In this study, we explore the use of deuterium (D) and hydrogen (H) interdiffusion during laser scanning (employing a continuous wave laser at 532 nm wavelength) to characterize both quantities. The evaluation of temperature from hydrogen diffusion data requires knowledge of the high temperature (T > 500 °C) deuterium-hydrogen (D-H) interdiffusion Arrhenius parameters for which, however, no experimental data exist. Using data based on recent model considerations, we find for laser scanning of single films on glass substrates a broad scale agreement with experimental temperature data obtained by measuring ...

The effects of postdeposition air exposure of microcrystalline silicon films, prepared at varied deposition rates, are investigated. The changes in the oxygen content, evaluated from Fourier transform infrared spectroscopy measurements, were studied over a period of time after deposition (up to 180 days) depending on deposition rate and Raman intensity ratio. Two types of behavior were identified: in the case of highly crystalline samples, an oxygen uptake increases with increasing Raman intensity ratio; while less crystalline samples were found to be more stable against oxygen incorporation. These observations are related to the film microstructure and porosity and are linked to the variations in Raman intensity ratio and growth rate of microcrystalline silicon films.

The influence of implanted hydrogen (up to a concentration level of 3 at. %) on the microstructure of silicon (Si) materials is investigated by Fourier transform infrared spectroscopy as well as by effusion of hydrogen and of (low dose) implanted helium. Three materials of low original hydrogen concentration, crystalline Si, electron beam evaporated amorphous Si, and plasma-deposited hydrogenated amorphous Si (using high deposition temperature) were investigated. Significant differences between crystalline and amorphous materials were observed. In crystalline Si, implanted hydrogen is found to generate multivacancies that trap diffusing helium while this is not the case in amorphous Si. Accordingly, cavities where hydrogen is located in amorphous Si must be smaller than divacancies. Those cavities in amorphous Si, present from the growth process, that trap helium tend to disappear when the implanted hydrogen concentration increases. Annealing of the materials up to temperatures of 575 °C was also studied. No significant change in the density of voids (trapping helium) occur but in case of crystalline Si the bonding sites of hydrogen as well as the diffusion paths of helium change.

This study addresses the electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide (ZnO:Al) films. The main focus was on the improvement in carrier mobility mu to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity. The influence of Al concentration in the target, film thickness, sputter power, deposition pressure, and substrate temperature on material properties was investigated. The structural, compositional, electrical and optical properties were studied using x-ray diffraction, secondary ion mass spectrometry (SIMS), room temperature Hall effect measurements and spectral photometry, respectively. All ZnO:Al films were polycrystalline and preferentially oriented along [002]. The grain size along the direction of growth increased with higher Al doping and with increasing film thickness. The SIMS measurements revealed that the Al concentration in the film was nearly the same as in the target. Carrier concentration N and mobility mu are determined by the target Al concentration. In addition mu is influenced by the film thickness and the sputter pressure. For each Al concentration, the highest mu was generally observed at low deposition pressures. By using a target with low Al2O3 concentration of 0.5 wt %, mu could be improved up to 44.2 cm(2)/V s while maintaining the electrical resistivity rho as low as 3.8x10(-4) Omega cm. For these films the transparency in the near-infrared wavelength range strongly improved which makes them particularly interesting for the application in optoelectronic devices like thin-film solar cells. The mu-N dependence for films deposited under diverse conditions was studied to identify a practical limit for mu. (C) 2004 American Institute of Physics.

Microcrystalline silicon carbide (μc-SiC:H) deposited by hot wire chemical vapor deposition (HWCVD) and plasma-enhanced chemical vapor deposition (PECVD) provide advantageous opto-electronic properties, making it attractive as a window layer material in silicon thin-film and silicon heterojunction solar cells. However, it is still not clear which electrical transport mechanisms yield dark conductivities up to 10−3 S/cm without the active use of any doping gas and how the transport mechanisms are related to the morphology of μc-SiC:H. To investigate these open questions systematically, we investigated HWCVD and PECVD grown layers that provide a very extensive range of dark conductivity values from 10−12 S/cm to 10−3 S/cm. We found out by secondary ion mass spectrometry measurements that no direct correlation exists between oxygen or nitrogen concentrations and high dark conductivity σd, high charge carrier density n, and low activation energy Ea. Higher σd seems to rise from lower hydrogen concentrations or/and larger coherent domain sizes LSiC. On the one hand, the decrease of σd with increasing hydrogen concentration might be due to the inactivation of donors by hydrogen passivation that gives rise to decreased n. On the other hand, qualitatively consistent with the Seto model, the lower σd and lower n might be caused by smaller LSiC, since the fraction of depleted grain boundaries with higher Ea increases accordingly.

SIMS depth profiling, using an oxygen primary beam at close to normal incidence, was applied to study lithium diffusion in thin films of hydrogenated amorphous silicon (a-Si:H) as well as in layered structures of doped and undoped silicon-based alloys. A strongly increasing decay length of the lithium profiles was observed for increasing primary beam energies and is attributed to the Li accumulation at the SiOx/Si interface. The stability of the lithium incorporation in a-Si:H is found to depend on the presence of charged acceptors or defects and of doping gradient related electrical fields.

The influence of oxygen and nitrogen impurities on the performance of thin-film solar cells based on microcrystalline silicon (mu c-Si:H) has been systematically investigated. Single mu c-Si:H layers and complete mu c-Si:H solar cells have been prepared with intentional contamination by admitting oxygen and/or nitrogen during the deposition process. The conversion efficiency of similar to 1.2 mu m thick mu c-Si: H solar cells is deteriorated if the oxygen content in absorber layers exceeds the range from 1.2 x 10(19) to 2 x 10(19) cm(-3); in the case of nitrogen contamination the critical impurity level is lower ([N](critical)=6 x 10(18)-8 x 10(18) cm(-3)). It was revealed that both oxygen and nitrogen impurities thereby modify structural and electrical properties of mu c-Si:H films. It was observed that the both contaminant types act as donors. Efficiency losses due to oxygen or nitrogen impurities are attributed to fill factor decreases and to a reduced external quantum efficiency at wavelengths of >500 nm. In the case of an air leak during the mu c-Si:H deposition process, the cell performance drops at an air leak fraction from 140 to 200 ppm compared to the total gas flow during i-layer deposition. It is demonstrated that oxygen and nitrogen impurities close to the p/i-interface have a stronger effect on the cell performance compared to impurities close to the n/i-interface. Moreover, thick mu c-Si:H solar cells are found to be more impurity-sensitive than thinner cells. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3104781]

An improved version of a data processing and control system has been used with state-of-the-art AES and SIMS instruments. It consists of a mainframe with CPU, buffer and IEEE 488 interface to a host computer and a range of plug-in submodules. Its features include three-dimensional analysis, imaging, multichannel spectra and sample bias control. The performance of the system has been tested by AES and SIMS depth profile measurements of Si-Ge multilayers.

The influence of atmospheric contaminants oxygen and nitrogen on the performance of thin-film hydrogenated amorphous silicon (a-Si:H) solar cells grown by plasma-enhanced chemical vapor deposition at 13.56 MHz was systematically investigated. The question is addressed as to what degree of high base pressures (up to 10(-4) Torr) are compatible with the preparation of good quality amorphous silicon based solar cells. The data show that for the intrinsic a-Si: H absorber layer exists critical oxygen and nitrogen contamination levels (about 2 x 10(19) atoms/cm(3) and 4 x 10(18) atoms/cm(3), respectively). These levels define the minimum impurity concentration that causes a deterioration in solar cell performance. This critical concentration is found to depend little on the applied deposition regime. By enhancing, for example, the flow of process gases, a higher base pressure (and leak rate) can be tolerated before reaching the critical contamination level. The electrical properties of the corresponding films show that increasing oxygen and nitrogen contamination results in an increase in dark conductivity and photoconductivity, while activation energy and photosensitivity are decreased. These effects are attributed to nitrogen and oxygen induced donor states, which cause a shift of the Fermi level toward the conduction band and presumably deteriorate the built-in electric field in the solar cells. Higher doping efficiencies are observed for nitrogen compared to oxygen. Alloying effects (formation of SiOx) are observed for oxygen contaminations above 10(20) atoms/cm(3), leading to an increase in the band gap. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3009384]

Fur die unendliche anisotrop-elastische Ebenc wird der Einflus von zwei Grundsingularrtalen, der Einzelkraft und der Stufenversetzung, auf die Airysche Spannungslunktion, den Spannungsfunktionsvektor und den Spannungstensor sowie den Verschiebungsvektor und den Distorsionstensor berechnet. Der Vorteil der dargestellten Methode besteht darin, das die Materialkonstanten in ubersichtlicher Form zu kompakten tensoriellen und quasi-tensoriellen Grosen zusammengefast und gewisse Analogien zwischen den betrachteten zehn Einflusfunktionen deutlich werden.

Fur die unendliche anisotrop-elastische Ebene wird der Einflus der Einzelkraft und des Kraftedipols sowie der Keilversetzung, der Stufenversetzung und des Stufenversetzungsdipols auf die Airysche Spannungsfunktion, den Spannungsfunktionsvektor und den Spannungstensor sowie auf den Verschiebungsvektor und den Distorsionstensor berechnet. Dabei konnen alle auftretenden Materialkonstanten zu kompakten tensoriellen und quasi-tensoriellen Grosen zusammengefast werden. Wie im isotropen Fall lassen sich Singularitaten und Zustandsgrosen einander zuordnen; daher weisen die Einflusfunktionen gewisse Symmetrien bzw. Identitaten auf, und zwischen den Materialgrosen besteht eine Reihe wichtiger Verknupfungen.

A method is given, in a compact, schematized form, of representing the fundamental solutions for the infinite orthotropic plane. Attention is particularly focused on the tensorial and “quasi-tensorial” structure of the orthotropic-elastic factors which occur in the influence functions. It is shown that the proposed formulation leads directly to the limiting case of isotropic material.

Basis for the presented method is the knowledge of certain fundamental solutions for theinfinite anisotropic medium. By superimposing these singular solutions in a suitable fashion, the given boundary value problem can be formulated as a tensorial integral equation (singularity method).

It is well known that a “one to one” analogy (slab analogy) exists for all steps of the formulation of plane-elasticity and slab-deflection problems. The object of this paper is to reveal this analogy also for the most important statical and geometrical singularities and for the fundamental solutions which depict the influence of the singularities on the elastic state of deformation, with special emphasis on anisotropic material. Therefore state variables, differential equations, singularities and elastic constants of both problems are composed systematically and compared with each other, and it is shown in which way the fundamental solutions of the first problem change into those of the second.

The occurrence of metallic conductivity in SrTiO3 single crystals is reported for reduction under low partial pressure of oxygen at 800 degrees C. This transition is shown to result from the formation of a high concentration of vacancy defects along a network of extended defects within the skin region. A self-healing phenomenon is observed for progressive reduction which causes the concentration of initially introduced defects to decrease in the course of heat treatment and leads to a breakdown of the metallic conductivity as well as a substantial loss of optical subgap absorption.