Metal-organic chemical vapor deposition of cerium oxide, gallium-indium-oxide, and magnesium oxide thin films: Precursor design, film growth, and film characterization.

摘要

A new class of volatile, low-melting, fluorine-free lanthanide metal-organic chemical vapor deposition (MOCVD) precursors has been developed. The neutral, monomeric cerium, neodymium, gadolinium, and erbium complexes are coordinatively saturated by a versatile, multidentate, ether-functionalized β-ketoiminate ligand, and complex melting point and volatility characteristics can be tuned by altering the alkyl substituents on the ligand periphery. Direct comparison with lanthanide β-diketonate complexes reveals that the present precursor class is a superior choice for lanthanide oxide MOCVD. Epitaxial CeO ₂ buffer layer films have been grown on (001) YSZ substrates by MOCVD at significantly lower temperatures than previously reported using one of the newly developed cerium precursors. High-quality YBCO films grown on these CeO₂ buffer layers by POMBE exhibit very good electrical transport properties. The cerium complex has therefore been explicitly demonstrated to be a stable and volatile precursor and is attractive for low-temperature growth of coated conductor multilayer structures by MOCVD.; Gallium-indium-oxide thin films (Ga_xIn_2−xO ₃), x = 0.0∼1.1, have been grown by MOCVD using the volatile metal-organic precursors In(dpm)₃ and Ga(dpm)₃. The films have a homogeneously Ga-substituted, cubic In₂O₃ microstructure randomly oriented on quartz or heteroepitaxial on (100) YSZ single-crystal substrates. The highest conductivity of the as-grown films is found at x = 0.12. The optical transmission window and absolute transparency of the films rivals or exceeds that of the most transparent conductive oxides known. Reductive annealing results in improved charge transport characteristics with little loss of optical transparency. No significant difference in electrical properties is observed between randomly oriented and heteroepitaxial films, thus arguing that carrier scattering effects at high-angle grain boundaries play a minor role in the film conductivity mechanism.; The synthesis and characterization of a new magnesium MOCVD precursor, Mg(dpm)₂(TMEDA) is detailed. It is shown that the donating ligand TMEDA prevents oligomerization and subsequent volatility depression as observed in the commonly used [Mg(dpm)₂]₂. The superiority of Mg(dpm)₂(TMEDA) as an MOCVD precursor is explicitly demonstrated by growth of epitaxial MgO thin films on single-crystal SrTiO₃ substrates.