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The Seebeck coefficient is the most widely measured property specific to thermoelectric materials. There is currently no consensus on measurement protocols, and researchers employ a variety of techniques to measure the Seebeck coefficient. The implementation of standardized measurement protocols and the use of reliable Seebeck Coefficient Standard Reference Materials (SRMs® ) will allow the accurate interlaboratory comparison and validation of materials data, thereby accelerating the development and commercialization of more efficient thermoelectric materials and devices. To enable members of the thermoelectric materials community the means to calibrate Seebeck coefficient measurement equipment, NIST certified SRM® 3451 "Low Temperature Seebeck Coefficient Standard (10K to 390 K)". Due to different practical requirements in instrumentation, sample contact methodology, and thermal stability, a complementary SRM® is required for the high temperature regime (300K to 900 K). The principal requirement of a SRM® for the Seebeck coefficient at high temperature is thermocyclic stability. We therefore characterized the thermocyclic behavior of the Seebeck coefficient for a series of candidate materials: constantan, p-type single crystal SiGe, and p-type polycrystalline SiGe, by measuring the temperature dependence of the Seebeck coefficient as a function of 10 sequential thermal cycles, between 300K and 900 K. We employed multiple regression analysis to interpolate and analyze the thermocyclic variability in the measurement curves. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

Research describing the dynamic characteristics of dislocations within silicon crystals doped with boron is presented. The etch pit technique is used to investigate the effects of varying boron concentrations.

We generalize in this work the constitutive model for silicon crystals of Alexander and Haasen. Strain-rate and temperature dependency of the mechanical behavior of intrinsic crystals are correctly accounted for into stage I of hardening. We show that the steady-state of deformation in stage I is very well reproduced in a wide range of temperature and strain rate. The case of extrinsic crystals containing high levels of dissolved oxygen is examined. The introduction of an effective density of mobile dislocations dependent on the unlocking stress created by oxygen atoms gathered at the dislocation cores is combined to an alteration of the dislocation multiplication rate, due to pinning of the dislocation line by oxygen atoms. This increases the upper yield stress with the bulk oxygen concentration in agreement with experimental observations. The fraction of effectively mobile dislocations is found to decay exponentially with the unlocking stress. Finally, the influence of oxygen migration back onto the dislocations from the bulk on the stress distribution in silicon bars is investigated. [ABSTRACT FROM AUTHOR]

We report on the crystallinity, N incorporation efficiency, optical properties, and electrical properties of N and Te codoped ZnO films grown by plasma-assisted molecular-beam epitaxy. Te improves the surface morphology and roughness of ZnO films in terms of both streak reflection high energy electron diffraction pattern and atomic force microscopy observations. Also, N and Te codoping is helpful to improve the crystallinity and N incorporation efficiency simultaneously. We found that; (a) narrower x-ray linewidth and higher N concentration were obtained by codoping. (b) Nitrogen related emission lines including donor-acceptor pair and acceptor-bound exciton dominantly emerged in photoluminescence spectra. (c) Codoping enhanced the carrier compensation of native donors in ZnO films and suppressed the dislocation scattering. As a consequence, we concluded that N and Te codoping is very effective for the growth of reliable p-type ZnO films which fulfill the controversial requirements; high N concentration and high crystallinity, simultaneously. [ABSTRACT FROM AUTHOR]

Variation in stacking fault energy with annealing at 1173 K were identified in Czochralski-grown silicon crystals heavily doped with n- or p-type dopant atoms. In n-type crystals, the energy decreased with increasing annealing time. The higher the concentration of dopant atoms, the larger the degree of the decrease. On the other hand, the energy was unchanged during annealing in p-type and nondoped crystals. These results imply that n-type dopant atoms segregate nearby a stacking fault, via their thermal migration, under an electronic interaction leading to a reduction in the stacking fault energy. [ABSTRACT FROM AUTHOR]

Constitutive modeling of silicon materials is currently restricted to the very early stage of deformation. Uniaxial tensile testing of monocrystals oriented for single glide is traditionally simulated by a scalar model relying on the so-called machine equation. The present work uses a crystal plasticity framework to identify the role of secondary slip systems in the yield region. A three-dimensional finite element model of a tensile apparatus is validated by comparison of its outputs to the results yielded by a scalar formulation. Best fits of the constitutive model of Alexander and Haasen to experimental data reveal strong variations in its parameters with temperature. An improved constitutive model for intrinsic silicon monocrystals deformed in single slip is described. Its parameters are identified as analytical functions of temperature. We show its excellent agreement with the observed steady state of deformation in stage I. [ABSTRACT FROM AUTHOR]

Optical properties of wurtzite ZnO bulk single crystals in which an arbitrary number (typically 109–1010 cm-2) of fresh dislocations were introduced intentionally by the plastic deformation at elevated temperatures (923–1073 K) were examined. Deformed specimens showed excitonic light emission with photon energies of 3.100 and 3.345 eV, as well as their LO phonon replicas at 11 K. The light intensities increased with increasing dislocation density. The activation energy for a thermal quenching of the 3.100 or 3.345 eV emission band, which corresponds to the depth of the localized energy level associated with the emission band, was estimated to be 0.3±0.1 or 0.05±0.01 eV, respectively. The origin of the energy levels was proposed as point defect complexes involving dislocations. The introduction of the dislocations at the elevated temperatures above 923 K did not influence the intensities of the emission bands except the dislocation-related emission bands. [ABSTRACT FROM AUTHOR]

The mechanical strength of bulk single crystal wurtzite ZnO was investigated at elevated temperatures by means of compressive deformation. The yield stress of ZnO in the temperature range of 650–850 °C was found to be around 10–20 MPa, i.e., extremely lower than that of GaN, a typical wide band-gap semiconductor. On the basis of the observed temperature dependence of yield stress, the activation energy for dislocation motion at elevated temperatures in ZnO is deduced to be 0.7–1.2 eV, which follows the relation of activation energy for dislocation motion versus band-gap energy known in a variety of semiconductors. [ABSTRACT FROM AUTHOR]

Heavily impurity-doped single crystals of SixGe1-x alloy with the composition 0.84

We have investigated the characteristic of the dislocations in the ZnO layers grown on c sapphire by the plasma-assisted molecular beam epitaxy under the different Zn/O flux ratios. The ZnO layers were characterized by the transmission electron microscopy (TEM) and the high-resolution x-ray diffraction (HRXRD). The TEM and HRXRD experiments revealed that the major threading dislocations (TDs) in the ZnO layers are the edge dislocations running along the c axis with Burgers vector of 1/3«11–20». The TD densities are determined to be 6.9×109, 2.8×109, and 2.7×109 cm-2, for O-rich, stoichiometric, and Zn-rich grown ZnO, respectively. Different from the O-rich grown ZnO where the dislocations run along the c-axis, several dislocations in the stoichiometric and the Zn-rich grown ZnO are inclined to 20°∼30° from the c-axis. By considering the slip system in the wurtzite-structure ZnO, the glide planes of the dislocations are close to (10-10) for the O-rich grown ZnO and close to (10-11) for the stoichiometric and Zn-rich grown ZnO. Furthermore, the thickness of the interface dislocations in the O-rich grown ZnO is much thinner than in the stoichiometric and Zn-rich grown ZnO. In addition, the most probable origin of the inclined dislocations including c/a ratios, growth rate, and initial growth stage of high temperature (HT)-ZnO layers are also discussed. [ABSTRACT FROM AUTHOR]

We report diffusion experiments of Au in highly dislocated, undoped and homogeneously doped Si with B concentrations of 3.0×1019 and 1.7×1020 cm-3. After Au diffusion at temperatures between 800 and 1100 °C, Au profiles were measured by means of neutron-activation analysis in conjunction with serial sectioning. The diffusion of Au in dislocated Si is accurately described on the basis of the kick-out mechanism and an additional reaction which takes into account the capture of interstitial Au at dislocations. The profiles yield data for the boundary concentration CAu0 and the Au diffusion coefficient DAu whose product CAu0DAu equals the transport capacity CAuieqDAui of interstitial Aui. With increasing B doping Au diffusion increases showing that interstitial Au is singly positively charged. An enhanced boundary concentration CAu0 and simultaneously retarded Au diffusivity was observed at temperatures below 1000 °C which provides direct evidence of Au segregation at dislocations. A segregation enthalpy of 2.7 eV for the energy difference of Au atoms dissolved on substitutional lattice sites and Au atoms trapped at dislocations was determined. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dynamic behavior of dislocations in heavily germanium (Ge)-doped silicon (Si) crystals with concentrations up to 2.5 × 10[sup 20] cm[sup -3], and Ge and boron (B) codoped Si crystals with concentrations of 4×10[sup 19] and 9×10[sup 18] cm[sup -3], respectively, is investigated using the etch pit technique in comparison with that in undoped and B-doped Si crystals. Strong suppression of the generation of dislocations from a surface scratch is found for Ge and B codoped Si in comparison with that observed for Ge-doped and B-doped Si. The velocity of dislocations in Ge and B codoped Si crystals is found to be lower than that of dislocations in B-doped, Ge-doped, and undoped Si. The coexistence of Ge and B impurities in Si is considered to be effective at immobilizing and retarding the velocity of dislocations in Si. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the alpha and beta dislocations' dynamic behavior in undoped and impurity-doped InAs crystals, using the etch pit technique. Structure of the III-V compound semiconductor crystals; Details on the dislocation velocity; Expression of the measurement of the velocities; Results of the study.

The dynamic behavior of dislocation in heavily Ge-doped Si crystals and Ge and B codoped Si crystal has been investigated which demonstrates strong suppression of dislocation generation in Si codoped with Ge and B, while weak suppression occurs in Ge-doped Si and the critical stress increases gradually with increasing Ge concentration. This is interpreted in terms of dislocation immobilization due to the effective segregation of both Ge and B impurities.

Dislocation-oxygen impurity interaction in Czochralski-grown silicon crystals was influenced by treatments at temperature of 650 °C under a magnetic field up to 8 T. It was found that the critical stress for dislocation generation from a surface scratch varies with an intensity of the applied magnetic field and duration of the magnetic treatment. The generation of dislocations was effectively suppressed under certain conditions of the magnetic treatments. Such phenomena could not be detected in float-zone-grown silicon crystals. The results were discussed in terms of spin-dependent solid-state reaction in atomic bindings with impurity atoms around dislocation core, causing immobilization of dislocations in their macroscopic generation process. [ABSTRACT FROM AUTHOR]