Yi-Jie Xu

Zinc gallate (ZnGa₂O₄) thin films were grown on sapphire (0001) substrate using radio frequency (RF) magnetron sputtering. After the thin film deposition process, the grown ZnGa₂O₄ was annealed at a temperature ranging from 500 to 900 °C at atmospheric conditions. The average crystallite size of the grown ZnGa₂O₄ thin films increased from 11.94 to 27.05 nm as the annealing temperature rose from 500 to 900 °C. Excess Ga released from ZnGa₂O₄ during thermal annealing treatment resulted in the appearance of a Ga₂O₃ phase. High-resolution transmission electron microscope image analysis revealed that the preferential crystallographic orientation of the well-arranged, quasi-single-crystalline ZnGa₂O₄ (111) plane lattice fringes were formed after the thermal annealing process. The effect of crystallite sizes and lattice strain on the width of the X-ray diffraction peak of the annealed ZnGa₂O₄ thin films were investigated using Williamson-Hall analysis. The results indicate that the crystalline quality of the deposited ZnGa₂O₄ thin film improved at higher annealing temperatures.

In this paper, we report the growth and material characteristics of ZnGa₂O₄ thin films on c-plane sapphire and Si(100) substrates by a radio-frequency magnetron sputtering. When deposited on sapphire, the ZnGa₂O₄ film showed a polycrystalline nature and a less randomly oriented, primarily with the (111), (222) and (511) planes parallel to the substrate surface. On Si(100), the ZnGa₂O₄ thin film was randomly oriented with (311)- and (020)-plane polycrystalline properties. Transmission electron microscopy analysis revealed that an amorphous-layer interface was formed on the Si(100) substrate and the microstructure of ZnGa₂O₄ became disordered. The ZnGa₂O₄/sapphire emitted ultraviolet photoluminescence and green emissions. The dominant optical transitions depended on the deposition temperature, oxygen and Zn contents, and nature of the substrate. The structural and optical properties of sputter-deposited ZnGa₂O₄ thin film on sapphire indicated that sapphire substrate is suitable for the growth of crystalline, high-quality ZnGa₂O₄ thin film.

Yttrium fluoride (YF₃) films were grown on sapphire substrate by a radio frequency magnetron using a commercial ceramic target in a vacuum chamber. The structure, composition, and plasma etching behavior of the films were systematically investigated. The YF₃ film was deposited at a working pressure of 5 mTorr and an RF power of 150 W. The substrate-heating temperature was increased from 400 to 700 °C in increments of 100 °C. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction results confirmed an orthorhombic YF₃ structure was obtained at a substrate temperature of 700 °C for 2 h. X-ray photoelectron spectroscopy revealed a strongly fluorinated bond (Y–F bond) on the etched surface of the YF₃ films. HRTEM analysis also revealed that the YF₃ films became yttrium-oxyfluorinated after exposure to fluorocarbon plasma. The etching depth was three times lower on YF₃ film than on Al₂O₃ plate. These results showed that the YF₃ films have excellent erosion resistance properties compared to Al₂O₃ plates.