Preparation and properties of thermally evaporated lead germanate films

Abstract

Ferroelectric lead germanate (Pb₅Ge₃O₁₁) films were fabricated by thermal evaporation on n-type silicon substrates. Characterization of the films was made on the basis of substrate temperature, rate of evaporation, annealing time and temperature, and their interdependence. The crystallinity of the film depends on the substrate temperature; films grown at room temperature are amorphous. At high substrate temperatures crystalline films can be obtained, but the as-grown films which were crystalline in nature were found to be nonferroelectric. The conductivity of these films was very much higher than that of the bulk crystals. This may be attributed to O₂ deficiency in the films. The loss of stoichiometry was recovered by annealing the films in an atmosphere of Pb and O₂ at 600° C for 6 h. A clear dielectric anomaly, offset in the dc conductivity near the transition temperature, and good hysteresis loops were observed in the annealed films of thickness ≳1 µm.