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
Agency: Department of Defense | Branch: Defense Advanced Research Projects Agency | Program: SBIR | Phase: Phase II | Award Amount: 275.50K | Year: 1993
LARGE, HIGH QUALITY CDZNTE SINGLE CRYSTALS AREREQUIRED AS HGCDTE EPITAXIAL SUBSTRATES IN THE MANUFACTURE OF INFRARED FOCAL PLANE ARRAYS. BRIDGMAN GROWTH PROCESSES ARE CURRENTLY EMPLOYED TO PRODUCE MATERIALS WHICH MEET SOME APPLICATION REQUIREMENTS, BUT FALL SHORT IN MANY STATE-OF-THE-ART EPITAXIAL HGCDTE DEVICES. BRIDGMANTECHNIQUES, BEING MELT PROCESSES, ARE STRONGLY INFLUENCED BY INTRICATE COUPLING BETWEEN HEAT AND MASS TRANSFER AND METAL FLOW. THE PROCESSES ARE CONTROLLED BY REGULATING SYSTEM GEOMETRIES, GROWTH RATES, AMBIENT ATMOSPHERES AND APPLIED THERMAL GRADIENTS. PROCESS INTRICACIES ANDDEVIATIONS HAVE A PARTICULARLY LARGE EFFECT ON CDTE FAMILY CRYSTAL QUALITY DUE TO PARTICULARLY LARGE EFFECT ON CDTE FAMILY CRYSTAL QUALITY DUE TO THE LOW THERMAL CONDUCTIVITIES, STACKING FAULT ENERGIES AND YIELD STRENGTHS OF THESE MATERIALS. THIS PROJECT WILL STUDY THE APPLICATION OF INTELLIGENT PROCESSING OF MATERIALS (IPM) TECHNIQUES TO BRIDGMAN CDZNTE CRYSTAL GROWTH. THE OBJECTIVES OF HIGHER QUALITY, HIGHER YIELD AND LOWER COST WILL BE SOUGHT THROUGH THE APPLICATION OF ADVANCED SENSORS, INTELLIGENT ASSESSMENT AND ADAPTIVE CONTROL. IN PHASE I, AN ADVANCED TEMPERATURE SENSOR SYSTEM WILL BE DEVELOPED AND DEMONSTRATED AND THE CONCEPTUAL DESIGN OF AN IPM SYSTEM WILL BE PERFORMED. DURING PHASE II, IPM CONTROL OF METAL CONVECTION, LIQUID/SOLID INTERFACE SHAPE, GROWN-IN STRESS, DISLOCATION GENERATION, PRECIPITATE FORMATION AND/OR IMPURITY SEGREGATION WILL BE DEMONSTRATED. ANTICIPATED BENEFITS/POTENTIAL COMMERCIAL APPLICATIONS - IPM ENHANCED PRODUCIBILITY OF CDZNTESUBSTRATES WILL DRIVE HIGHER QUALITY, HIGHER YIELD HGCDTE EPITAXIAL MATERIALS LEADING TO HIGHER PERFORMANCE, LOWER COST IR FOCAL PLANE ARRAYS. THESE DEVICES WILL ENHANCE MANY DOD INFRARED SYSTEMS AND, IF COSTS ARE LOW ENOUGH, ENABLE COMMERCIAL IR
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 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