Date of Graduation

1999

Document Type

Dissertation/Thesis

Abstract

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) studies have been performed on two chalcopyrite crystals grown by the horizontal-gradient-freeze technique. An impurity defect has been characterized in silver gallium selenide (AgGaSe2) and has been identified as a Ni+ ion substituting for a Ag+ ion. This nickel defect exists in as-grown crystals in the paramagnetic state. A complete ENDOR angular dependence study provided spin-Hamiltonian parameters for the 61Ni isotope as well as the neighboring selenium ions (77Se) and gallium ions (69Ga and 71Ga). Optical absorption data taken at room temperature and low temperature showed a broad band peaking near 2.2 microns. The zero-phonon line position was determined from the low temperature data. The EPR and optical absorption data were consistent with each other, suggesting the absorption band was associated with Ni+ impurities. Two point defects have been identified and characterized in zinc germanium phosphide (ZnGeP 2). The first is a copper impurity, which substitutes for a zinc ion in the ZnGeP2 lattice. The copper impurity acts as a conventional acceptor and is not paramagnetic in the as-grown condition, i.e., the light-off condition. Upon illumination of the sample with 633-nm or 1064-nm light, the copper acceptor gives up an electron and becomes paramagnetic. The EPR spectrum consists of resolved hyperfine due to the copper nucleus (63Cu and 65Cu) as well as neighboring phosphorous nuclei ( 31P). The spin-Hamiltonian parameters have been determined from ENDOR measurements of the light-induced EPR spectrum. The second defect that has been studied in ZnGeP2 is the previously identified zinc vacancy (VZn). EPR and ENDOR studies have previously characterized the g values and primary hyperfine interactions associated with the VZn. Further ENDOR measurements have been made in order to identify hyperfine interactions with more distant phosphorous neighbors. The results led to spin-Hamiltonian parameters for five weaker phosphorous hyperfine interactions. The previous EPR and ENDOR results have been combined with these recent ENDOR measurements to give a complete characterization of the zinc vacancy in ZnGeP2. This work has been supported by the Air Force Office of Scientific Research (Grant #F-49620-96-1-0452) and the National Science Foundation (Grant #DMR-9807128).

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