In situ crystallization study of impurity phases in Bi–Fe–O thin films grown by atomic layer deposition

Abstract

We report on the phase evolution of pure and Fe-doped bismuth oxide (Bi–O and Bi–Fe–O) thin films grown by atomic layer deposition. In situ X-ray diffraction was used to map the evolution of phase formation and orientational growth of the oxides during the gradual crystallization of the films from the amorphous state on single-crystalline substrates. The formation of (001)-oriented Bi₂O_2.3 was observed at temperatures as low as 300 °C on (001)SrTiO₃, with a gradual transformation into Bi₂O₃. A similar crystallization of Fe-doped Bi₂O₃ on (111)ZrO₂(Y₂O₃) leads to the formation of (111)-oriented δ-Bi₂O₃ above 400 °C instead of the sillenite phase. We thus demonstrate that epitaxial stabilization of the metastable phases can take place during atomic layer deposition of oxides as well as post-deposition annealing. In situ crystallization of the amorphous Bi–Fe–O films revealed the evolution of oxide phases in the film with the sillenite composition. Our results are important for the design of annealing procedures to obtain phase-pure epitaxial BiFeO₃ thin films from amorphous stoichiometric Bi–Fe–O grown by atomic layer deposition.