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Title: Growth and Characterization of Epitaxial ZnO Thin Films on GaN(0001) Epilayers and ZnO{0001} Substrates Using Metalorganic Chemical Vapor Depositon
Authors: Pierce, Jonathan Mark
Advisors: Dr. Douglas Barlage, Committee Member
Dr. George Rozgonyi, Committee Member
Dr. Robert Davis, Committee Chair
Keywords: epitaxial
thin films
Issue Date: 29-Jun-2005
Degree: MS
Discipline: Materials Science and Engineering
Abstract: ZnO thin films were produced on GaN(0001) epilayers and ZnO(0001) substrates utilizing an iterative process requiring a structured low temperature (480°C) layer followed by a high temperature (800°C) densification step to create approximately 200 nm of contiguous film. This process is subsequently repeated to achieve thicker films with each iteration producing approximately 200 nm of dense film. Diethylzinc was used as the zinc source, UHP oxygen (O2) as the oxygen source, and UHP argon as both the carrier and diluent gas. Nitrous (N2O) and nitric oxide (NO2) were also used both as potential oxygen sources in the pure state as well as mixed with oxygen in the chamber and for nitrogen doping of the growing film. Major impurities of C, H, and N were incorporated into the films with the majority of the incorporation occurring during the low temperature step. Films grown using N2O + O2 contained an average of 5 x 1017 cm-3 atomic nitrogen while films using NO2 + O2 had an average nitrogen concentrations of 9 x 1019 cm-3. Needle microstructures were observed for low temperature layers using O2 and N2O + O2, while networked structures formed when using NO2 + O2. The surface of the densified films contained hexagonal pits that increased in number and depth with an increase in film thickness. Triple-axis XRD measurements indicated that the crystal structure of the films mimic the underlying substrates. A comparative analysis of undoped and N-doped films using capacitance voltage and photoluminescence measurements showed that the N-doped films were more insulating than the undoped films and the incorporation of nitrogen decreases the amount of excitonic peaks observed in the PL spectra. The 3.367 eV ionized donor bound exciton becomes dominant in N-doped films relative to the 3.361 eV donor bound exciton that dominates the undoped films. A preliminary inductively coupled plasma etching study determined that the smoothest sidewalls and surfaces were obtained using an ICP power of 600 W, a DC bias of 50 V, 5 mtorr total pressure, and 20 sccm of pure flowing BCl3 The etch rate under these conditions was 40 nm/min.
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