|M.Sc Student||Nijikovsky Boris|
|Subject||Microstructural Characterization of ZnO Films Deposited on|
(111)-MgAl2O4 from Low Temperature Aqueous
|Department||Department of Materials Science and Engineering||Supervisor||Professor Wayne D. Kaplan|
|Full Thesis text|
ZnO is considered a promising candidate material for advanced technological devices. Various methods for synthesizing ZnO epitaxial films exist, e.g. vapor phase deposition and liquid solution techniques. The relatively simple process of low temperature (≤ 100°C) aqueous synthesis is particularly attractive, and is the focus of this research. The main goals of this study were to evaluate the microstructure of ZnO films produced by low temperature aqueous synthesis, and to gain a better understanding of the nucleation and film growth mechanisms during film formation.
ZnO films (~4 μm thick) were deposited on single crystal (111)-MgAl2O4 substrates by a two-step aqueous synthesis process at 90°C at the University of California, Santa Barbara. During the first step a thin ZnO seed layer (~200 nm) was deposited under nucleation promoting conditions, followed by annealing at 500°C. A subsequent growth stage was used to thicken the films, followed by annealing treatments for 4 hours at different temperatures under flowing nitrogen.
Preferred orientation and phase analyses were performed by backscattered electron and X-ray diffraction, respectively. Scanning electron microscopy was used to characterize the surface morphology, and transmission electron microscopy (TEM) was performed in cross-section to determine the ZnO polarity, to characterize defects in the films, and to characterize the ZnO-MgAl2O4 interface.
Film nucleation and growth mechanisms are proposed based on grain size distribution analysis and the observed microstructural details. The high density of defects (dislocations and voids) are discussed with respect to possible growth mechanisms, and compared to the microstructure resulting from other ZnO deposition methods.