Heteroepitaxial Growth of a TaN Thin Film with Clear Anisotropic Optical Properties.

TaN is a promising semiconductor photocatalyst which can generate H gas from water under visible light illumination. It is expected that TaN 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 TaN single-crystalline thin films by solid phase epitaxy on the (110) plane of perovskite LaAlO substrates. The obtained epitaxial thin films of TaN exhibited clear optical anisotropy (pleochroism) as predicted by previous first-principles calculations. The optical gap for ||[100] polarization (∼2.12 eV) was smaller than that for ||[100] polarization (∼2.27 eV).