Epitaxial oxide thin films grown by solid source metal-organic chemical vapor deposition.

摘要

The conventional liquid source metal-organic chemical vapor deposition (MOCVD) technique is capable of producing large area, high quality, single crystal semiconductor films. However, the growth of complex oxide films by this method has been hampered by a lack of suitable source materials. While chemists have been actively searching for new source materials, the research work reported here has demonstrated the successful application of solid metal-organic sources (based on tetramethylheptanedionate) to the growth of high quality thin films of binary compound cerium dioxide (CeO{dollar}sb2{dollar}), and two more complex materials, the ternary compound lithium niobate (LiNbO{dollar}sb3{dollar}), with two cations, and the quaternary compound strontium barium niobate (SBN), with three cations.; The growth of CeO{dollar}sb2{dollar} thin films on (1012)Al{dollar}sb2{dollar}O{dollar}sb3{dollar} substrates has been used as a model to study the general growth behavior of oxides. Factors affecting deposition rate, surface morphology, out-of-plane mosaic structure, and film orientation have been carefully investigated. A kinetic model based on gas phase prereaction is proposed to account for the substrate temperature dependence of film orientation found in this system. Atomically smooth, single crystal quality cerium dioxide thin films have been obtained. Superconducting YBCO films sputtered on top of solid source MOCVD grown thin cerium dioxide buffer layers on sapphire have been shown to have physical properties as good as those of YBCO films grown on single crystal MgO substrates.; The thin film growth of LiNbO{dollar}sb3{dollar} and Sr{dollar}sb{lcub}1-x{rcub}{dollar}Ba{dollar}sb{lcub}x{rcub}{dollar}Nb{dollar}sb2{dollar}O{dollar}sb6{dollar} (SBN) was more complex and challenging. Phase purity, transparency, in-plane orientation, and the ferroelectric polarity of LiNbO{dollar}sb3{dollar} films grown on sapphire substrates was investigated. The first optical quality, MOCVD grown LiNbO{dollar}sb3{dollar} films, having waveguiding losses of less than 2 dB/cm, were prepared. An important aspect of the SBN film growth studies involved finding a suitable single crystal substrate material. MgO (100) was found to be a useful substrate material for growing (001)-oriented SBN films. However, four in-plane grain orientations coexisted under certain conditions. The volume fraction of the mixed grains was dependent on source composition and not by deposition rate, substrate temperature, cooling rate, or deposition method. The single phase existence region for SBN films was found to deviate from that in the equilibrium phase diagram. Near optical quality films were obtained.; The results found in this study on three quite different oxide materials indicate that solid source MOCVD can provide excellent film quality, exceeding or competitive with physical vapor deposition techniques.