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Title: Thin Film Growth and Doping Characteristics of ZnO and beta-Ga2O3
Authors: Porter, Hugh Lawson
Advisors: Jagdish Narayan, Committee Co-Chair
John Muth, Committee Co-Chair
Robert Kolbas, Committee Member
Veena Misra, Committee Member
Keywords: transmission electron microscopy
zinc oxide
gallium oxide
thin films
pulsed laser deposition
isoelectronic impurities
Issue Date: 20-Jan-2005
Degree: PhD
Discipline: Electrical Engineering
Abstract: ZnO films have been prepared through both pulsed laser deposition (PLD) and pulsed electron deposition (PED). The films grown through PLD have been co-doped with tellurium and nitrogen to compensate for ZnO's natural n-type behavior and have been shown to be highly resistive. A discussion of the isoelectronic impurity, tellurium, and the p-type impurity, nitrogen, and their compensating mechanisms is given. A Kaufman ion source was used to incorporate atomic nitrogen into ZnO films, and the impact of N₂⁺ ions with the ZnO film is proposed as the cause of breaking the nitrogen molecules into individual atoms. Tellurium has been incorporated into the films by mixing a small amount of ZnTe in the source material. The films are not strongly p-type, but resistivity and photoconductive responsivity have been shown to increase with doping concentration, suggesting donor compensation and more intrinsic films. There appears to be an optimal percentage of incorporated tellurium of 0.5%, at which both of these properties are at a maximum, and this is suggested to be a solubility limit for this process. Time-resolved photoluminescence shows a much shorter excess carrier life-time in the doped films, which implies that the enhanced photoconductivity is indeed due to the films being more intrinsic. Epitaxial β-Ga₂O₃ has been prepared through pulsed electron deposition. The epitaxial growth relationship is given, and shown to be due to domain matching epitaxy. X-ray diffraction (XRD), and high resolution transmission electron microscopy (HR-TEM) confirm the relationship between film and substrate. Finally, optical absorption measurements provide an optical band gap of 4.96 eV.
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