Density Of Structural Defects Research Articles

Fast Method to Determine the Structural Defect Density of 156 x 156 mm2 Mc-Si Wafers

Today a remaining challenge is to determine the structural defect density (SDD) on a whole 156 x 156 mm2 multicrystalline (mc) silicon wafer over a timescale of a few minutes. In this contribution a new method is introduced to determine the SDD on large scale mc-Si wafers. The main advantage of the method presented is the possibility to obtain a complete map of the SDD of a 156 x 156 mm2 mc-Si wafer as well as a quantitative SDD analysis of the wafer in just a few minutes. Furthermore, the simple and quick sample preparation as well as the application of standard measurement equipment results in a convenient and cost-effective analysis tool. With these advantages, analysis of SDDs on large quantities of wafers, e.g. across the ingot height or width, can be easily realized in a few hours.

Analysis of Mono-cast Silicon Wafers and Solar Cells on Industrial Scale

Mono-cast silicon recently became available in volumes relevant for industrial scale production of solar cells. At the present time, mono-cast wafers are classified by an optical determination of the <100>-grain area on the wafer. This paper discusses solar cell efficiency distributions of mono-cast wafers which we obtained in first tests using an industrial cell process. A screening process based on the optical classification turns out to be insufficient in order to obtain a narrow efficiency distribution. We used photoluminescence imaging as an additional fast inspection tool for wafers and solar cells. Prominent defects of mono-cast wafers were investigated using photoluminescence, electroluminescence and reverse biased electroluminescence (ReBEL) imaging as well as the structural defect density (SDD) method on a laboratory scale.

Microstructure and Phase Transformation Behavior of a Stress-Assisted Heat-Treated Ti-Rich NiTi Shape Memory Alloy

In this study, the effects of stress-assisted heat treatment on the microstructure and phase transformation of a Ti-rich (Ti-49.52 at.% Ni) shape memory alloy were investigated. For this purpose, the alloy was heat treated at temperature of 500 °C for 10 h under applied stresses of 100 and 200 MPa. XRD, TEM, and repeated thermal cycling were employed to study the microstructure and transformation behavior of the heat-treated materials. Room temperature XRD diffractogram of the stress-free heat-treated material showed a weak reflection of austenite (B2), while that for the stress-assisted heat-treated materials had a high intensity implying the presence of residual austenite in the microstructure. TEM observations confirmed the presence of residual austenite and revealed mechanical twins as another constituent of the microstructure in the stress-assisted heat-treated materials. Moreover, with increasing the value of applied stress the size of mechanical twins was increased and a high density of structural defects was observed at the interfaces of the twins. DSC results demonstrated two-stage transformation in the initial cycles of transformation in the stress-assisted heat-treated material. After about eight cycles of transformation, the two-stage transformation has vanished, and a single-stage transformation remained up to 100 cycles. It was suggested that the accommodation of stresses at Ti2Ni/matrix interface provides a suitable condition for local transformation of B2 to B19′ that is manifested by a two-stage phase transformation. Introduction of structural defects during repeated thermal cycling may counteract the stress field at Ti2Ni/matrix interface leading to a single-stage transformation.

Evolution of carbon film structure during its catalyst-free growth in the plasma of direct current glow discharge

Catalyst-free growth of nanocrystalline carbon films on silicon substrates under direct current glow discharge in a mixture of hydrogen and methane was studied by scanning and transmission electron microscopy, Raman spectroscopy, as well as X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy (BESSY II, Berlin). The in-time development of the film structure on a carbided silicon substrate includes the formation of diamond-like particles, ultra-thin graphite flakes parallel to the surface, carbon nanowalls nucleated on the stacked flakes and their growth accompanied by a permanent decrease of the structural defect density, and finally nanotube nucleation at the nanowall edges. Based on the observation of the carbon nanotube/nanowall linear size variation in time and using the calculated binding energies and the diffusion thresholds obtained from the literature, we propose that direct attachment of the CH 3 radicals to the carbon nanowall edge is the predominant mechanism and the rate-limiting step of its growth, whereas carbon nanotube growth is controlled by radicals diffusing along its outer surface.

Effects of Buffer Layer on Structure and Ferromagnetism of Co-Doped SnO$_{2}$ Films

The thickness of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers has been found to considerably affect the structure and magnetic properties of Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films. As the buffer-layer thickness increases, the lattice constant <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> and Co-O bond length of the Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films contract, which suggest the gradual relaxation of the accumulated tensile strain. Simultaneously, the amount of structural defects in Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films decreases significantly and the grain size increases with increasing buffer-layer thickness. All the Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films exhibit intrinsic ferromagnetism at room temperature and the saturated magnetic moment varies with the buffer-layer thickness. The dependence of ferromagnetism on the buffer-layer thickness can be explained on the basis of the variations in the density of structural defects and Co-O bond length in Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films.

Effect of Zn incorporation into CuInS2 solar cell absorbers on microstructural and electrical properties

Zn incorporation into CuInS2 absorbers is found to increase the open-circuit voltage but decrease the short-circuit current of the corresponding thin-film solar cells. In this article, we study the effect of Zn incorporation into CuInS2 absorbers with a focus on the mechanisms leading to the measured changes in the electrical properties of the solar cells. Solar cells with varying Zn concentrations in their absorbers are characterized via the application of transmission electron microscopy, quantum efficiency, and current-voltage measurements, as well as admittance, x-ray photoelectron and photoluminescence spectroscopy. A Zn accumulation on the absorber side of the CuInS2–CdS interface and a higher structural defect density within the absorber are found after Zn incorporation. Capacitance, quantum efficiency, and current-voltage measurements in combination with device simulations suggest that Zn incorporation induces or enhances a shallow donor at the CuInS2–CdS interface. The interface defect pins the Fermi level close to the CdS conduction band, leading to an inversion at the heterointerface and thus reducing the recombination at interface defects and increasing the open-circuit voltage. A shallow bulk acceptor about 0.15 eV above the valence band edge is observed to increase with increasing Zn concentration in the CuInS2 absorbers and is responsible for a gradual decrease in the short-circuit current and the gain in the open-circuit voltage as the Zn concentration increases.

Phase Transition of Octaneselenolate Self-assembled Monolayers on Au(111) Studied by Scanning Tunneling Microscopy

We investigated the surface structure and wetting behavior of octaneselenolate self-assembled monolayers (SAMs) on Au(111) formed in a 50 ethanol solution according to immersion time, using scanning tunneling microscopy (STM) and an automatic contact angle (CA) goniometer. Closely-packed, well-ordered alkanethiol SAMs would form as the immersion time increased; unexpectedly, however, we observed the structural transition of octaneselenolate SAMs from a molecular row phase with a long-range order to a disordered phase with a high density of vacancy islands (VIs). Molecularly resolved STM imaging revealed that the missing-row ordered phase of the SAMs could be assigned as a superlattice containing three molecules in the rectangular unit cell. In addition, CA measurements showed that the structural order and defect density of VIs are closely related to the wetting behaviors of octaneselenolate SAMs on gold. In this study, we clearly demonstrate that interactions between the headgroups and gold surfaces play an important role in determining the physical properties and surface structure of SAMs.

Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (&amp;lt;400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (∼50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

Electronic structure of Co2+ions in anatase Co:TiO2in relation to heterogeneity and structural defects

We have studied the electronic structure of Co ions in semiconducting anatase Co:TiO2(1.4 at.% Co) with x-ray-absorption spectroscopy. The density of structural defects is varied by (i) the oxygen vacancy concentration depending on the oxygen background pressure during growth, and (ii) the film thickness. TheCoL2,3-edge spectra, which are characteristic of Co2+ (3d7) ions, show particularly pronounced ligand-to-metal charge-transfer (CT) satellites for the thickest oxygen-poor films, which also exhibit the highest structural defect density. With charge-transfer multiplet calculations, the CT satellites are modeled by configuration interaction, originating from hybridization between Co 3d- and ligand states. This hybridization adds to the complex interplay between Co heterogeneity, defects, and electronic and magnetic properties in Co:TiO2.

Tuning the Conduction Mechanism in Niobium-Doped Titania Nanoparticle Networks

Networks of niobium-doped TiO2 anatase nano- particles with variable doping concentrations were investigated by time-domain terahertz spectroscopy and microwave impe- dance spectroscopy. A detailed description of their electromag- netic response is proposed; the model takes into account the depolarization fields of inhomogeneous samples and allows us to understand the conductive and dielectric response of in- dividual nanoparticles. We find that electron hopping is the dominating contribution to the conductivity at terahertz fre- quencies and that the dielectric losses of TiO2nanoparticles are enhanced in comparison with bulk anatase. The conductive properties of nanoparticles can be tuned via synthesis conditions and thermal posttreatment.In particular, annealing at elevated temperatures improves the nanoparticle crystallinity, reduces the density ofstructuraldefects,andenhancestheconductivepercolationofthenetwork.Thedevelopedmodeloftheconductionprocessescan be helpful for interpretation of charge transport in other semiconducting nanoscale materials.

Creation of Face-to-face π-π Stacking of Fused Acene Backbones by Aryl-perfluoroaryl Interactions and Induction of Charge Transport Properties

ABSTRACTThe charge transport properties critically depend on the degree of ordering of the chains in the solid state as well as on the density of chemical or structural defects. In general, goodelectronic performance requires strong electronic coupling between adjace nt molecules in the solid-state that yield strong intermolecular π-overlap. Herein, we newly designed and synthesized organic semiconducting materials having both aryl (Ar) and perfluoroaryl (FAr) as substituents for organic electronics along with molecular packing control. Regarding this molecular design, we hypothesized and expected that the Ar and FAr substituents would induce well-defined π-π stacking structure of charge transport units for high performance organic electronics devices.

Ultrasonic Spectroscopy of Silicon Single Crystal

Specimens of Si single crystals with different crystal orientation [100] and [110] were studied by ElectroUltrasonic Spectroscopy (EUS) and Resonant Ultrasonic Spectroscopy (RUS). A silicon single crystal is an anisotropic crystal, so its properties are different in different directions in the material relative to the crystal orientation. EUS is based on interaction of two signals: an electric AC signal and an ultrasonic signal, which are working on different frequencies. The ultrasonic wave affects the charge carriers’ transport in the structures and the intermodulation electrical signal which is created due to the interaction between the ultrasonic wave and charge carriers, is proportional to the density of structural defects. RUS enables to measure natural frequencies of free elastic vibrations of a simply shaped specimen by scanning a selected frequency range including the appropriate resonances of the measured specimens.

Electrical Properties of Pt/n-Ge Schottky Contact Modified Using Copper Phthalocyanine (CuPc) Interlayer

We investigated the electrical properties and reverse leakage mechanisms of Pt/n-Ge Schottky contacts with copper phthalocyanine (CuPc) as an interlayer. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Schottky contacts were used to evaluate Schottky barrier parameters such as ideality factor, barrier height, and series resistance. The barrier heights and ideality factors measured from the forward bias I-V characteristics were found to be 0.50 eV and 1.06 for Pt/n-Ge Schottky contact, and 0.58 eV and 1.31 for Pt/CuPc/n-Ge Schottky contact, respectively. Cheung method was used to measure the series resistances of the Schottky contacts, and the consistency was checked using the Norde method. The reverse leakage conduction mechanism of the Schottky contacts was investigated. Pt/CuPc/n-Ge Schottky contacts showed a transition from Schottky emission to Poole-Frenkel emission at a higher bias range. This could be associated with the high density of structural defects or traps associated with the organic material.

Membrane-assisted revelation of the spatial nanoarchitecture of dislocation networks

We propose a method of direct visualization of the spatial nanoarchitecture of dislocation networks which is based on etching away the regions with low density of structural defects from the bulk of GaN epilayers, keeping intact only the threading dislocations and a thin surface film pre-treated with low-energy Ar + ions. The formation of nanometer-thick suspended membrane to which the dislocations are genetically attached provides conditions for the revelation of the spatial nanoarchitecture of dislocation networks using conventional scanning electron microscopy. Complementary monochromatic and panchromatic micro-cathodoluminescence images are presented.

Quantitative structure-and-energy analysis of heat treatment of structural steel

The microhardness, coercive force, resistivity, and structure of steel 45 are studied. The concept of structural interface is used to develop a quantitative parameter of organization of the micro- and mesostructures, which characterizes the density of the crystal structure defects. The relation between this parameter and the physical and mechanical properties of structural steel 45 is determined.

Study of Ion-Beam-Induced Damage and Luminescence Properties in Terbium-Implanted AlGaN

Terbium (Tb) ions were implanted into Al0.35Ga0.65N epitaxial layers at room temperature to investigate ion-beam-induced damage and luminescence properties at various doses of 1×1012–2.8×1016 Tb/cm2. Rutherford backscattering spectrometry/channeling (RBS/channeling) reveals that ion-beam-induced damage level steeply increases and that the damage cannot be fully suppressed even after rapid thermal annealing at 1100 °C, when the dose exceeds 5×1014 Tb/cm2. However, cathodoluminescence (CL) intensity related to Tb3+ transitions increased initially and saturated above a dose of 1×1013 Tb/cm2. Furthermore, transient decay time determined by time-resolved photoluminescence (TRPL) decreased faster and a fast decay component related to the formation of nonradiative Tb-defect complexes became dominant, as Tb ion dose increases. Therefore, the results suggest that Tb-related luminescence properties are much susceptible to defects and nonradiative defects, namely, Tb-defect complexes, are formed under low-dose conditions even at a very low structural defect density.

Strain-induced lateral self-organization in Si/SiO2 nanostructures

We show that strain, arising from the mismatch between Si and SiO2 thermal expansion coefficients, directs the thermal crystallization of amorphous Si along Si/SiO2 interfaces, and produces continuous, fully crystallized nanometer thick Si layers with a lateral-to-vertical aspect ratio close to 100:1. These Si nanolayers exhibit a low density of structural defects and are found to be elastically strained with respect to the crystal Si substrate.

Nucleation of Epitaxial Graphene on SiC(0001)

A promising route for the synthesis of large-area graphene, suitable for standard device fabrication techniques, is the sublimation of silicon from silicon carbide at elevated temperatures (>1200 degrees C). Previous reports suggest that graphene nucleates along the (110n) plane, known as terrace step edges, on the silicon carbide surface. However, to date, a fundamental understanding of the nucleation of graphene on silicon carbide is lacking. We provide the first direct evidence that nucleation of epitaxial graphene on silicon carbide occurs along the (110n) plane and show that the nucleated graphene quality improves as the synthesis temperature is increased. Additionally, we find that graphene on the (110n) plane can be significantly thicker than its (0001) counterpart and appears not to have a thickness limit. Finally, we find that graphene along the (110n) plane can contain a high density of structural defects, often the result of the underlying substrate, which will undoubtedly degrade the electronic properties of the material. Addressing the presence of non-uniform graphene that may contain structural defects at terrace step edges will be key to the development of a large-scale graphene technology derived from silicon carbide.

The features of temperature dependence of contact resistivity of Au-Ti-Pd2Si-p+-Si ohmic contacts

We consider the features of formation of AuTiPd ohmic contacts to p + -Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metalSi interface. + -Si.

Electrical and electrothermal transport in InN: The roles of defects

The transport properties of Mg doped and undoped InN films are studied with capacitance-voltage, thermopower, and Hall mobility measurements. A positive Seebeck coefficient is observed for Mg doped InN confirming p-type conductivity, though high doping and structural defect density can lead to n-type films. Transport measurements of undoped films are analyzed employing Rode's iterative Boltzmann equation method. Observed thermopower, Hall mobility, and dislocation density data for undoped films are consistent with calculations including the effects of charged line defect (donor-type dislocation) scattering.