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Title:Phonon scattering from substitutional impurities and lattice defects in cadmium sulfide
Author(s):Moore, Glenn Ellis
Doctoral Committee Chair(s):Klein, Miles V.
Department / Program:Physics
Subject(s):phonon scattering
substitutional impurities
lattice defects
cadmium sulfide
thermal conductivity
Abstract:The thermal conductivity as a function of temperature has been measured from 1.4°K to 80 0K for doped and pure cadmium sulfide single crystals of the wurtzite structure. The crystals were grown by a modified Bridgeman technique under 100 atmospheres of argon at 1100°C by the Eagle Picher Corporation. The experimental results for the pure crystals indicate the heat flow is isotropic in the crystal; the thermal conductivity parallel to the c-axis is identical to the conductivity perpendicular to the c-axis. It is also found that etching the crystals in HC1 gives a "perfectly rough" surface for boundary scattering of phonons. A theoretical analysis utilizing the Debye thermal conductivity integral was successfully applied to the data for the pure crystal. Coefficients derived from computer fits to the data agree with those calculated from theoretical phonon scattering rates. Isoe1ectronic, substitutional impurities (Co, Mn, Ni, Se, and Zn) were introduced in the melt in concentrations up to 500 ppm. A Debye fit, using only enhanced point defect scattering, to the thermal conductivity data for the doped crystals works well except at the lowest temperatures. To match the low temperature data it was necessary to include a term Ym in the inverse of the phonon relaxation time. It i$ suggested that lattice imperfections, in particular dislocations, may cause the low temperature depression of the thermal conductivity. Theoretical studies by Klemens, Carruthers, and Ohashi of phonon scattering by dislocations were compared and the re5lUlts applied to cadmium sulfide. Dislocation densities determined from etch pit counts on the doped crystals were a factor of 10 lower than those predicted by the above theories and computer fits to the data. Phonon scattering by magnetic levels of the transition metal dopants (Co, Mn, and Ni) was also considered. The low temperature depression of the thermal conductivity of the 500 ppm Co-doped sample may be due to the splitting of the magnetic energy levels in the cobalt ion by the electric field of the cadmium sulfide lattice. Magnetic level scattering was not detected in the Mn-and Ni-doped crystals. Heat treatments were used to study the effects of stoichiometry and electronic compensation on the thermal conductivity of the pure and doped samples. Heating in flowing argon does not change the electrical or thermal conductivity of the sample. It is postulated that this indicates the crystals are stoichiometric. Heating the samples in a sealed sulfur atmosphere induces photoconductivity but has no effect on the thermal conductivity.
Issue Date:1968
Genre:Dissertation / Thesis
Rights Information:1968 Glenn Ellis Moore, Jr.
Date Available in IDEALS:2011-07-11
Identifier in Online Catalog:6085726

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