Growth and characterization of zinc oxide thin films produced by metalorganic vapor phase epitaxy

ZnO thin films were grown in a metalorganic vapor phase epitaxy system constructed at North Carolina State University for use in this research. The system utilized radio frequency induction heating and could accommodate samples just under two inches in diameter. Diethylzinc was used as the zinc source, UHP oxygen as the oxygen source, and UHP argon as both the carrier and diluent gas. Films grown at a temperature of 500°C, a total growth pressure of 40 torr, and an O₂:DEZ ratio of 320:1 on both GaN epilayers and bulk ZnO(0001) substrates were found to be monocrystalline and a sharp interface was observed between the substrate and film, as verified by high-resolution transmission electron microscopy. A large number of dislocations were observed in the all of the ZnO films grown, however, films grown on GaN epilayers appeared to have a higher density of threading dislocations, many of which were generated at the GaN/ZnO interface. Atomic force microscopy and X-ray photoelectron spectroscopy were used to examine the growth mechanism of ZnO on GaN epilayers. It was found that growth proceeded via Volmer-Weber, or 3-D island growth. The film morphology was studied by scanning electron microscopy. It was found that films grown above 550°C were polycrystalline with a columnar morphology while those grown below 500°C had a higher degree of surface roughness than those grown at 500°C. Growth on both the zinc-terminated and oxygen-terminated face of ZnO(0001) substrates was investigated. It was found that films grown on the zinc-terminated face had a lower degree of surface roughness than those grown on the oxygen-terminated face. High-resolution transmission electron microscopy of homoepitaxial films showed them to be monocrystalline and lattice matched with the substrate.