Influence of post-annealing on structural, electrical and optical properties of manganese oxide thin films grown by atomic layer deposition

Manganese oxide films are fabricated on silicon wafer by an atomic layer deposition method. The effects of different post-annealing temperatures on the valence of the manganese and the crystal structure and electrical and optical properties of the films have been studied. It is found that the oxidation state of the manganese decreases with increasing post-annealing temperature. The chemical composition of the films as-deposited and post-annealed at lower temperature is β-MnO₂ and transforms into Mn₂O₃ when the post-annealing temperature is higher than 600°C. The electrical resistivity of the β-MnO₂ films decreases from 3.10 Ω·cm to 1.12 Ω·cm with the post-annealing temperature increasing. These samples exhibit stronger absorption in the visible light region. After being post-annealed at temperature higher than 600°C, the films exhibit higher electrical resistivity and higher transmittance in the visible light region. These results indicate that the post-annealing is an effective method to modify the electrical and optical properties of manganese oxides and useful for the applications of manganese oxide films in microelectronic and optoelectronic devices.