Heteroepitaxial Growth of a Ta₃N₅ Thin Film with Clear Anisotropic Optical Properties

Ta₃N₅ is a promising semiconductor photocatalyst which can generate H₂ gas from water under visible light illumination. It is expected that Ta₃N₅ exhibits a strong anisotropy in its physical properties stemming from its highly anisotropic crystal structure. However, such anisotropic properties have not been verified experimentally due to the difficulty in synthesizing a large single crystal. Here, we report the synthesis of (010)-oriented Ta₃N₅ single-crystalline thin films by solid phase epitaxy on the (110) plane of perovskite LaAlO₃ substrates. The obtained epitaxial thin films of Ta₃N₅ exhibited clear optical anisotropy (pleochroism) as predicted by previous first-principles calculations. The optical gap for E||[100] polarization (∼2.12 eV) was smaller than that for E||[100] polarization (∼2.27 eV).