AlN films have been successfully deposited by plasma CVD for the first time. Al was supplied by trimethyl Al (TMA) with H2 or N2 carrier gas, and N was supplied as NH3 through separate gas lines. The deposition rate depends upon the TMA supply, and is essentially independent of the NH3 flow rate. The composition of the deposited films was almost AlN, although a small amount of oxygen was always detected. A better film was obtained for the H2 carrier gas than for N2 carrier gas. X-ray diffraction profiles of the deposited films exhibited no crystalline AlN diffracting peaks, suggesting that the films are not crystallized, but the infrared and ultraviolet absorption spectra exhibited the presence of the Al–N bond (650/cm) and an optical band gap of 5.55 eV. The refractive index was about 1.9. These results suggest that the plasma-deposited films possess dominant AlN properties even though they are not crystalline.
Thin films of BaTiO3 and SrTiO3 and their superlattice were grown on SrTiO3 substrates using oxygen from the substrates as an oxygen source. Epitaxial growths were carried out by coevaporations of the component metals under ultrahigh vacuum without introducing any oxidants. The growth mechanism in the extremely low oxidation ambient was studied. Oxygen was automatically fed from the substrate to the growing film surface. As a result, oxygen vacancies were incorporated deep into the inside of the SrTiO3 substrate, confirmed by means of positron annihilation. The local oxygen deficiency at the growing surface is buffered by the fast diffusion of incorporated oxygen vacancies into deep inside of the substrate, avoiding decomposition or nucleation of the metallic phases on the surface. The BaTiO3/SrTiO3 interfaces were formed without intermixing, despite considerable amounts of oxygen having moved through the interfaces.
A high-quality BaTiO3 thin film on SrTiO3 substrate was obtained by shutting off the oxygen supply during growth. Epitaxial growth of BaTiO3 film was carried out with molecular-beam epitaxy (MBE) under extremely low oxygen partial pressure (pO2<1×10-8 Pa). Although only Ba and Ti metals were supplied without introducing oxidant during the growth, a clear reflection high-energy electron diffraction (RHEED) intensity oscillation from layer-by-layer growth of BaTiO3 was observed. Oxygen was automatically fed from the substrate during the growth. The deposited film was found to have an approximately stoichiometric composition and single-phase of BaTiO3 from the analyses of Auger electron spectroscopy (AES) and X-ray diffraction (XRD).
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