PREPARATION OF ZINC TITANATE THIN-FILMS BY LOW-PRESSURE METALORGANIC CHEMICAL-VAPOR-DEPOSITION

Homogeneous thin films of zinc titanate have been successfully prepared on Si(100) wafers by depositing a film of zinc and titanium oxides (ZnO-TiO2) by low-pressure metalorganic chemical vapor deposition (MOCVD), followed by an annealing treatment, The precursors used for the deposition mere diethylzinc (DEZ), tetraisopropoxide titanium (TPT), and water. By performing the deposition at temperatures between 140 degrees and 350 degrees C, the stoichiometry of the as-deposited films could be effectively controlled over Zn/Ti ratios between 0.5 and 2.5, which cover the composition of various zinc titanate phases identified in the literature, The as-deposited ZnO-TiO2 films are amorphous, and possess a fairly smooth surface. XPS and SIMS analysis showed that the composition of these films is uniform over the wafer as well as through the film bulk. An annealing treatment of the as-deposited films at high temperature (650-800 degrees C) converted the amorphous ZnO-TiO2 into a zinc titanate crystalline structure, The conditions applied during the annealing treatment have a great effect on the composition and structure of the finally obtained zinc titanate films. By heating the as-deposited ZnO-TiO2 films to 800 degrees C at a rate of 600 degrees C/h, followed by keeping them at 800 degrees C for 2 h, the Zn/Ti atomic ratios of the annealed films remained nearly unchanged. The zinc titanate films consisted of large crystals having a size of hundreds of nanometers. The film with a Zn/Ti ratio of ca. 2 consisted of a Zn2TiO4 phase, which has a cubic inverse-spinel structure, The unit cell size of the Zn2TiO4 crystal is 8.433 Angstrom.