Some Electronic Properties of ZnO and SrTiO₃

Citation

Neville, Richard Coulston (1971) Some Electronic Properties of ZnO and SrTiO₃. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZF7V-1G45. https://resolver.caltech.edu/CaltechTHESIS:06132018-121037092

Abstract

The surface barrier systems consisting of gold and palladium on both chemically prepared and cleaved zinc oxide have been studied in detail. Surface barrier energies on non-degenerate chemically prepared zinc oxide were found to be 0.66 and 0.60 eV respectively for gold and palladium, as determined by four independent methods: photoresponse, current-voltage characteristics, thermal activation energy, and capacitance variation with voltage. The Bethe diode theory as modified by image force lowering was found to be an excellent description of the voltage-current characteristics. Thermionic field and pure tunneling currents were observed for surface barriers on degenerate zinc oxide at room and liquid nitrogen temperatures, respectively. The voltage dependence of these currents was in excellent agreement with the thermionic field and tunneling theories. Although dependence on impurity concentration was functionally in agreement with theory the predicted currents were too high by an order of magnitude. This effect is attributed to deficiencies in the theory.

The second material investigated was strontium titanate. The surface barrier systems consisting of gold, palladium, copper, and indium on both chemically prepared and cleaved single crystal strontium titanate were examined in detail. Surface barrier energies were determined, and the current versus voltage characteristics were examined in light of Bethe diode theory as modified by image force lowering. The relative permittivity of strontium titanate was determined over a temperature range from 4.2^°K to 300^°K as a function of applied electrical bias. No evidence of a ferroelectric transition was observed. A phenomonological description of the free energy involved in the titanium atom motion, which is responsible for the large relative permittivity, was derived. Evidence for domain interaction is discussed.

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