Wu P.,Ii Vi Inc.
Journal of Crystal Growth | Year: 2010
Extensive study of threading dislocations in 4H SiC crystals has been carried out using etching in molten KOH. In contrast to well-defined hexagonal pits formed on lightly doped 4H epilayers, etching of bulk 4H SiC crystals heavily doped with nitrogen produced rounded etch pits with their sizes varying in a wide range. Neither shape nor size of the etch pits in the bulk n+4H crystals could be used to distinguish between threading edge and treading screw dislocations. Data on the density of threading screw dislocations were obtained by counting etch pits on the carbon face of the wafers. Sequential steps of material removal, which included polishing followed by KOH etching, were used to track threading dislocations along the growth direction. It was found that a threading dislocation can produce etch pits of different sizes at different depths in the wafer. Mobility of the front of threading dislocations during growth was assessed by measuring change in the position of the dislocation etch pits upon sequential material removal. Statistical distribution of such displacements in the wafer plane was found to be lognormal. On average, the growth distance of 8 μm corresponded to the change in the etch pit position of about 2 μm. This shows that the front of threading dislocations has significant mobility during SiC sublimation growth, resulting in tilted or curved dislocation lines in the grown crystal. © 2009 Elsevier B.V. All rights reserved. Source
Ii Vi Inc. and II VI Incorporated | Date: 2011-10-18
Optical products, namely, lenses, reflectors, mirrors, windows, beam expander-condensers, waveplates, phase retarders, polarizer-analyzer-attenuators, thin film polarizers and electro-optical modulators.
Ii Vi Inc. | Entity website
Ii Vi Inc. | Entity website
II-VI Performance Metals division is an internationally recognized producer and supplier of rare specialty metals and chemical products. We are based in the Philippines, with global sales, marketing and customer support available through a combination of internal resources and distribution relationships ...
Kirkham M.J.,Oak Ridge National Laboratory |
Dos Santos A.M.,Oak Ridge National Laboratory |
Rawn C.J.,Oak Ridge National Laboratory |
Rawn C.J.,University of Tennessee at Knoxville |
And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012
Materials with the half-Heusler structure possess interesting electrical and magnetic properties, including potential for thermoelectric applications. MgAgSb is compositionally and structurally related to many half-Heusler materials but has not been extensively studied. This work presents the high-temperature x-ray diffraction analysis of MgAgSb between 27 and 420 ∼C, complemented with thermoelectric property measurements. MgAgSb is found to exist in three different crystal structures in this temperature region, taking the half-Heusler structure at high temperatures, a Cu 2Sb-related structure at intermediate temperatures, and a previously unreported tetragonal structure at room temperature. All three structures are related by a distorted Mg-Sb rocksalt-type sublattice, differing primarily in the Ag location among the available tetrahedral sites. Transition temperatures between the three phases correlate well with discontinuities in the Seebeck coefficient and electrical conductivity; the best performance occurs with the novel room temperature phase. For application of MgAgSb as a thermoelectric material, it may be desirable to develop methods to stabilize the room temperature phase at higher temperatures. © 2012 American Physical Society. Source