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Point Defects (point + defect)
Selected AbstractsObservation of Zn vacancies in ZnO grown by chemical vapor transportPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006F. Tuomisto Abstract We have used positron annihilation spectroscopy to study the vacancy defects in ZnO crystals grown by both the conventional and contactless chemical vapor transport (CVT and CCVT). Our results show that Zn vacancies or Zn vacancy related defects are present in as-grown ZnO, irrespective of the growth method. Zn vacancies are observed in CVT-grown undoped ZnO and (Zn,Mn)O. The Zn vacancies present in undoped CCVT-ZnO are the dominant negatively charged point defect in the material. Doping the material with As introduces also Zn vacancy-related defect complexes with larger open volume. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Predominant point defects in tellurium saturated CdTePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006P. Fochuk Abstract High temperature Hall effect measurements at 570,1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ,870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm,3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect , the oxygen interstitial acceptor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radiation induced modification of impurity-related point defects in crystalline quartz , a reviewCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006Harish Bahadur Abstract This article presents a short review of impurity-related point defects in crystalline quartz and their radiation induced modifications. In particular, a discussion has been presented on some of the prominent aluminum related alkali and proton compensated centers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High temperature arsenic doping of CdHgTe epitaxial layersCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2004A. Vlasov Abstract Experimental results on solid-state arsenic doping of the n-type bulk and ISOVPE epitaxial CdXHg1- XTe (X = 0.19 ÷ 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1- xTe films (nAs , 5 · 1016 ÷ 1 · 1020 cm -3; d = 2 ÷ 5 ,m) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 ÷ 600 °C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the Design of High-Efficiency Thermoelectric Clathrates through a Systematic Cross-Substitution of Framework ElementsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Xun Shi Abstract Type I clathrates have recently been identified as prospective thermoelectric materials for power generation purposes due to their very low lattice thermal conductivity values. The maximum thermoelectric figure of merit of almost all type I clathrates is, however, less than 1 and occurs at, or above, 1000,K, making them unfavorable especially for intermediate temperature applications. In this report, the Zintl,Klemm rule is demonstrated to be valid for Ni, Cu, and Zn transition metal substitution in the framework of type I clathrates and offers many degrees of freedom for material modification, design, and optimization. The cross-substitution of framework elements introduces ionized impurities and lattice defects into these materials, which optimize the scattering of charge carriers by the substitution-induced ionized impurities and the scattering of heat-carrying lattice phonons by point defects, respectively, leading to an enhanced power factor, reduced lattice thermal conductivity, and therefore improved thermoelectric figure of merit. Most importantly, the bandgap of these materials can be tuned between 0.1 and 0.5,eV by adjusting the cross-substitution ratio of framework elements, making it possible to design clathrates with excellent thermoelectric properties between 500 and 1000,K. [source] Influence of Point-Defect Reaction Kinetics on the Lattice Parameter of Ce0.8Gd0.2O1.9ADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Anna Kossoy Abstract The kinetics of point-defect association/dissociation reactions in Ce0.8Gd0.2O1.9 and their influence on the crystal lattice parameter are investigated by monitoring thermally induced stress and strain in substrate- and self-supported thin films. It is found that, in the temperature range of 100,180,°C, the lattice parameter of the substrate-supported films and the lateral dimensions of annealed, self-supported films both exhibit a hysteretic behavior consistent with dissociation/association of oxygen vacancy,aliovalent dopant complexes. This leads to strong deviation from linear elastic behavior, denoted in the authors' previous work as the "chemical strain" effect. At room temperature, the equilibrium state of the point defects is reached within a few months. During this period, the lattice parameter of the substrate-supported films spontaneously increases, while the self-supported films are observed to transform from the flat to the buckled state, indicating that formation of the dopant,vacancy complex is associated with a volume increase. The unexpectedly slow kinetics of establishing the defect equilibrium at room temperature can explain the fact that, depending on the sample history, the "observable" lattice parameters of Ce0.8Gd0.2O1.9, as reported in the literature, may differ from one another by a few tenths of a percent. These findings strongly suggest that the lattice parameter of the materials with a large concentration of interacting point defects is a strong function of time and material preparation route. [source] Periodic models in quantum chemical simulations of F centers in crystalline metal oxidesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007Yuri F. Zhukovskii Abstract We present a survey of recent first principles simulations of the neutral oxygen vacancies (F centers) existing as native or radiation-induced point defects in various crystalline metal oxides in different forms (bulk, bare substrate surface, and on the interface with metal adsorbates). We mainly consider periodic models in calculations of point defects using the metal oxide supercell or cyclic clusters. We compare different formalisms of first principles calculations, mostly the Density Functional Theory (DFT) as implemented in the framework of either localized basis set of atomic orbitals or delocalized basis sets of plane waves. We analyze in detail the structural and electronic properties of F centers in binary oxides of light metals (MgO and Al2O3), and ternary metal oxides (SrTiO3, BaTiO3, PbTiO3, KNbO3, and PbZrO3 perovskites). When available, we compare results of ab initio periodic defect calculations with experimental data, results of the first principles cluster calculations (both embedded and molecular) as well as with semi-empirical calculations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Theoretical Defect Energetics in Calcium Phosphate BioceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Katsuyuki Matsunaga Vacancies, impurities, and foreign ions dissolving in calcium phosphate bioceramics play an important role in the biological properties of the materials. However, little is known about the thermodynamic stability of the defects. In this regard, point defects in hydroxyapatite (HAp) and octacalcium phosphate (OCP) were calculated in a first-principles manner, and the chemical-potential dependence of the defect formation energies was revealed. In particular, because calcium phosphates are usually subjected to an aqueous solution, a methodology to evaluate ionic chemical potentials under chemical equilibrium of the solid,aqueous solution was introduced. In the present article, recent results based on such a methodology (the solution pH dependence of Ca/P molar ratio of HAp and the ion-exchange ability with foreign cations in HAp and OCP) were reviewed. [source] Single dopant diffusion in semiconductor technologyMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 2 2004A. Glitzky Abstract The paper deals with the analysis of pair diffusion models in semiconductor technology. The underlying model contains reaction-drift-diffusion equations for the mobile point defects and dopant-defect pairs as well as reaction equations for immobile dopants which are coupled with a non-linear Poisson equation for the chemical potential of the electrons. For homogeneous structures we present an existence and uniqueness result for strong solutions. Starting with energy estimates we derive further a priori estimates such that fixed point arguments due to Leray,Schauder guarantee the solvability of the model equations. Copyright © 2004 John Wiley & Sons, Ltd. [source] First-principles study on the concentrations of native point defects in high-dielectric-constant binary oxide materialsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2008J. X. Zheng Abstract The intrinsic concentrations of point defects in high- k binary oxide materials of HfO2, ZrO2, Y2O3 and La2O3 are evaluated on the basis of first-principles calculations. Oxygen defects are found to dominate over a wide range of the oxygen chemical potential. Neutral oxygen vacancies are likely to be responsible for electron trapping in the investigated materials. In HfO2 and ZrO2, oxygen Frenkel pairs are likely to form. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New direct evidence of point defects interacting with dislocations and grain boundaries in diamond,PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2005A. E. Mora Abstract The correlation of TEM imaging and micro-photoluminescence studies of electron irradiated areas of diamond, developed in Bristol, has been extended to new optical centres and defects. In this paper, we show new evidence of the interaction of point defects with dislocations and grain boundaries in diamond. Optical centres at 518.6 and 518.8 nm are directly correlated with dislocations and an optical centre at 519.1 nm was correlated with a grain boundary. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical resonant Raman spectra of nanotube (7,0) with point defectsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009Valentin N. Popov Abstract The Raman spectra of the nanotube (7,0) with point defects (monovacancy, divacancy, and Stone,Wales defect) were simulated in order to derive spectroscopic signatures of defective nanotubes. First, we calculated the electronic band structure and the phonon dispersion of the defective nanotubes using supercells within a non-orthogonal tight-binding model. We found that new optical transitions and Raman-active phonons appeared in comparison with the perfect nanotube. Secondly, we calculated the resonance Raman excitation profile for all Raman-active phonons of the defective nanotubes and simulated their Raman spectra at specific laser excitation energies. The predicted high-intensity Raman lines can be used as spectroscopic signatures of the defective nanotubes. [source] Identification of intrinsic defects in SiC: Towards an understanding of defect aggregates by combining theoretical and experimental approachesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2008Michel Bockstedte Abstract In SiC, mobile point defects may form thermally stable clusters and aggregates, such as di-vacancies or carbon interstitial complexes. Although predicted by theory, experimental evidence of such clusters became available only recently. Combining theoretical and experimental approaches, the unique identification of the di-vacancy, the carbon vacancy-antisite complex with the spin resonance centers P6/P7 and SI5 was recently achieved. In this way also the di-carbon and tri-carbon antisites with the photoluminiscence centers P,T and U, HT3 and HT4, respectively were identified. The two identified vacancy complexes show distinct properties: while the di-vacancy, like the silicon vacancy possesses a high-spin ground state, the carbon vacancy,antisite complex, like the carbon vacancy, is a Jahn,Teller center. These effects consistently explain the complex properties of the spin resonance spectra and are discussed in detail for the isolated vacancies. The aggregation of vacancies proved to be relevant in the explantation of the kinetic deactivation of nitrogen in co-implanted SiC. This and further evidence for defect aggregates underline the relevance of this notion. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Application of wavelength-resolved optically-detected XAS methods to phase-segregated silicatesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004N. R. J. Poolton Abstract Wavelength-resolved optically-detected X-ray absorption experiments are described that monitor the emission from naturally occurring phase-exsolved aluminosilicate feldspars, when exciting across the Ca and K L2,3 core levels. The results from a selection of example cases are presented that demonstrate the power of the technique in examining the structural and optical properties of phase segregated materials that could not easily be achievable by other methods. The results highlight that in these materials, extrinsic point defects such as Mn2+ and Fe3+ can also become preferentially associated with particular exsolved phases. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Positron annihilation studies of defects in Si1-xGex/SOI heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009A. Calloni Abstract The strain of a SiGe alloy epitaxially grown on Si can be released by heating at 750°C. However the strain relaxation is accompanied by the generation of threading dislocations and associated point defects. The attempted remedy is to let SiGe grow on a very thin Si substrate on top of a SOI heterostructure, with the purpose of concentrating the defects at the Si-SiO2 interface of the SOI substrate. A slow positron beam was used to investigate the effectiveness of the remedy. The positron diffusion length in SiGe decreases after the thermal treatment. This result shows the generation of lattice defects still occurs in the SiGe layer, in spite of the deposition on SOI. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure, chemistry and electrical properties of extended defects in crystalline silicon for photovoltaicsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2009M. Seibt Abstract The electronic properties of present-day multicrystalline silicon (mc-Si) materials for photovoltaic applications are strongly influenced by point defects, their mutual interaction and their interaction with dislocations and grain boundaries. This paper presents results from fundamental investigations of metal impurity interaction with extended defects, namely a small-angle grain boundary and bulk microdefects. It is shown that the distribution of copper silicide precipitates closely follows the density of bulk microdefects indicating the underlying physics of ,good' and ,bad' grains frequently observed in mc-Si. Co-precipitation of copper and nickel in the same samples leads to virtually the same distribution of multimetal silicide precipitates which according to light-beam induced current measurements show the same recombination activity as single-metal silicide particles. Transmission electron microscopy is used to show that for copper-rich and nickel-rich conditions two types of silicides co-exist, i.e. Cu3Si precipitates containing a small amount of nickel and NiSi2 precipitates containing some copper. Finally, phosphorus-diffusion gettering (PDG) is discussed as the main gettering process used in presentday silicon photovoltaics. Special emphasis is put on the effect of extended defects and their interaction with metal impurities on PDG kinetics. It is shown that different limiting processes will be simultaneously operative in mc-Si as a result of inhomogeneous bulk defect distributions (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dynamics of nanostructure formation using point defects on semiconductors by laser radiationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2009A. Medvid Abstract Dynamics of nanostructures (nanocones and nanocavties) formation on surface of semiconductors by laser radiation based on Thermogradient effect (TGE) is studied. Nanostructures formation of both nanohills and nanocavities are explained by point defects redistribution in gradient of temperature at the irradiated surface. Study of photoluminescence (PL), atomic force microscopy (AFM) and Raman back-scattering spectra speak in favour of presence of quantum confinement effect (QCE) on the top of nanocones on the irradiated surface of semiconductor single crystals. Aggregation of vacancies under the irradiated surface forms nanocavities. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Toward control of point defects in lithium fluoride thin layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007R. M. Montereali Abstract Point defect formation and stabilization properties, as well as their peculiar spectroscopic characteristics, locally modify the optical properties of insulating materials. Thin layers containing high concentrations of colour centres, hosted in a LiF single crystal and/or a polycrystalline matrix, offer the opportunity to develop innovative light-emitting photonic devices. Control of all the critical parameters should be required on spatial dimension comparable with the optical wavelengths. Recent developments in laser technologies, electron and particles beam methods, and novel photon sources, have opened a wide range of opportunities. An overview of the most significant advances in this field is provided, with particular emphasis on colour-centre LiF-based innovative miniaturised light sources, optical amplifiers and lasers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dependence of long-lived defect creation on excitation density in MgO single crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007Aleksandr Lushchik Abstract The processes of the creation, stabilization and annealing of anion Frenkel defects have been investigated in MgO and MgO:Be single crystals irradiated by , particles, uranium swift ions or fast neutrons at 300 K and also additionally irradiated by 5 keV electrons at 6 K. Neutral oxygen interstitials undergo stabilization due to their association with the holes localized near Be2+ ions or near cation vacancies. The peculiarities of the processes of nonimpact creation and stabilization of point defects under conditions of a high density of electronic excitations formed in the tracks of swift heavy ions have been considered by the example of MgO crystals, where the creation energy of a pair of long-lived Frenkel defects exceeds the energy gap, EFD > Eg. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] First-principles modelling of defects in advanced nuclear fuelsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007E. A. Kotomin Abstract In this paper we present and discuss the results of first first-principle modelling of point defects in nitride nuclear fuels. Calculations have been performed using the VASP computer code combined with supercells containing up to 250 atoms. The effective atomic charges, the electronic density redistribution, atomic displacements around U and N vacancies and their formation energies are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of CuInS2 crystals from melt and their propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006N. Satoh Abstract CuInS2 crystals are grown from the melt with the typical compositions which are stoichiometric, In2S3 and Cu2S excess ones and the effect of the melt composition on the melt growth is examined. Large grain size crystals are grown for the melt compositions except the case of Cu2S excess one. It is found that a small amount of CuIn5S8 is precipitated in In2S3 excess crystals by forming thin film layers in the bulk. From electrical conductivity and photo-luminescence (PL) spectra of the grown crystals, predominant native point defects characterizing their semi-conducting properties are discussed. As a result, it is suggested that native vacancy and the interstitial Cu play an important roles and a tentative band-diagram is proposed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Predominant point defects in tellurium saturated CdTePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006P. Fochuk Abstract High temperature Hall effect measurements at 570,1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ,870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm,3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect , the oxygen interstitial acceptor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The role of aluminium and titanium in the point defects of gamma irradiated natural quartzPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005G. O. Sawakuchi Abstract In this work, the origin of the smoky colour acquired by quartz when exposed to extremely high doses (20 kGy) of ionising radiation is studied. Five paramagnetic centres were detected in the electron paramagnetic resonance (EPR) spectrum of irradiated quartz: [AlO4]0, [TiO4,/Li+]0A, [GeO4,/Na+]0A, [GeO4,/Li+]0C, and E,1. Optical absorption revealed a complex spectrum with superposition of bands. With the technique of thermoluminescence, at least three peaks at around 180, 260 and 320 °C were detected. The peak at around 180 ºC has maximum emission at 470 nm and the peaks at around 260 and 320 °C have maximum emissions at 450 nm. Through correlations between the obtained results with these techniques, it was possible to confirm previous results from the literature, i.e., that the smoky colour of quartz is strongly related to the centre [AlO4]0. Besides, it was verified an excellent correlation between the thermal decay of [AlO4]0 and [TiO4,/Li+]0A, suggesting that at a temperature around 200 ºC the Li leaves the Ti centre and recombines with the aluminium centre destroying the smoky colour of irradiated quartz. On the other hand and differently from the literature this process does not correlate to any of the thermoluminescence peaks. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Giant reflectance anisotropy of polar cubic semiconductors in the far infraredPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2003Yu. A. Kosevich Abstract We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of GaAs(001) in the far infrared can reach the value of twenty percents which is two orders of magnitude higher than the reflectance difference of the GaAs(001) in the near-ultraviolet - visible range. The most strong reflectance anisotropy was observed in the optical phonon Reststrahlbande and its vicinity. We relate the observed reflectance anisotropy with the anisotropy of the optical-phonon and plasma damping constants. Such anisotropy can be caused by anisotropic inhomogeneous broadening of the frequencies of the optical-phonon and plasma oscillations polarized respectively along the [110] and directions. This effect can be understood in terms of the lattice-deformation-induced changes of the optical-phonon force constants and electron-effective-mass tensor components. Anisotropic inhomogeneous strain of the lattice can in turn be induced by anisotropic microscopic short-range ordering of point defects (dopants) and dislocations in near-surface regions of noncentrosymmentric zinc-blende semiconductors. The observed giant reflectance anisotropy can be used as a sensitive tool for the far infrared characterization of zinc-blende semiconductors. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Using dynamically scattered electrons for three-dimensional potential reconstructionACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2009Christoph T. Koch Three-dimensional charge-density maps computed by first-principles methods provide information about atom positions and the bonds between them, data which are particularly valuable when trying to understand the properties of point defects, dislocations and interfaces. This paper presents a method by which three-dimensional maps of the electrostatic potential, related to the charge-density map by the Poisson equation, can be obtained experimentally at 1,Å resolution or better, especially at low accelerating voltages. The method requires data acquired by holographic transmission electron microscopy methods such as off-axis electron holography or focal series reconstruction for slightly (e.g.±2°) different directions of the incident electron beam. The reconstruction of the three-dimensional electrostatic (and absorptive) potential is achieved by making use of changes in the dynamical scattering within the sample as the direction of the incident beam varies. [source] Thermodynamic Modelling of Defect Migration in Ferroelectric MaterialsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Oliver Goy Motivated by the phenomenon of electric fatigue, point defects and their interaction in ferroelectric material are studied with a focus on the tendency of clustering. The underlying continuum model takes into account the full anisotropic electromechanical material properties. Isotropic and anisotropic defect descriptions and their influence on defect interaction will be compared. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The electronic structure of chalcopyrites,bands, point defects and grain boundariesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2010Susanne Siebentritt Abstract We summarize the progress made recently in understanding the electronic structure of chalcopyrites. New insights into the dispersion of valence and conduction band allow conclusions on the effective masses of charge carriers and their orientation dependence, which influences the transport in solar cell absorbers of different orientation. Native point defects are responsible for the doping and thus the band bending in solar cells. Results of optoelectronic defect spectroscopy are reviewed. Native defects are also the source for a number of metastabilities, which strongly affect the efficiency of solar cells. Recent theoretical findings relate these effects to the Se vacancy and the InCu antisite defect. Experimentally determined activation energies support these models. Absorbers in chalcopyrite solar cells are polycrystalline, which is only possible because of the benign character of the grain boundaries. This can be related to an unusual electronic structure of the GB. Copyright © 2010 John Wiley & Sons, Ltd. [source] Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflectionsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2005Vladimir E. Dmitrienko Symmetry and physical aspects of `forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of `forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local `chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed. [source] Resonant X-ray diffraction: `forbidden' Bragg reflections induced by thermal vibrations and point defectsACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2000V. E. Dmitrienko In general, the local atomic environment becomes less symmetric owing to point defects and thermal vibrations of atoms in crystals. It is shown that, as a result of this phenomenon, an additional anisotropy of the resonant scattering factors can occur and the forbidden Bragg reflections can be excited near absorption edges. Examples of crystals are presented (Ge, K2CrO4, C-15 type) where such thermal-motion-induced (TMI) and point-defect-induced (PDI) reflections can be observed. The tensor structure factors of both types of reflection are computed. Owing to their resonant character, the PDI reflections allow both impurity atoms and host atoms of different types to be studied separately. The considered phenomena can provide a very sensitive method to study point defects because only the atoms distorted by defects produce contributions to the PDI reflections. [source] | |||||||||||||||||||