Bandgap engineering of tantalum nitride thin films by ion‑assisted magnetron sputtering for advanced electronic and radiation detection applications

Abstract

Tantalum nitride (TaN_x) thin films exhibit a wide range of electrical and optical properties that can be controlled by adjusting deposition conditions, making them attractive for microelectronics, protective coatings, and functional layers in radiation detectors and other advanced devices. In this work, TaN_x films were deposited by ion‑assisted reactive magnetron sputtering while systematically varying the N₂/Ar flow‑rate ratio. Optical transmission/reflectance spectroscopy combined with spectroscopic ellipsometry and the Tauc method analysis shows that increasing N₂/Ar flow-rate ratio governs a continuous transition from quasi-metallic Ta-rich films to semiconducting N-rich films, with indirect optical bandgaps increasing from near zero to about 1.6 eV. This transformation is accompanied by a corresponding increase in resistivity over roughly five orders of magnitude, from ~10^–2 to ~10³ Ω·cm. Raman spectroscopy and grazing-incidence X-ray diffraction reveal that all films are nanocrystalline or quasi-amorphous TaN_x with short-range order embedded in a disordered matrix; increasing N₂/Ar suppressing cubic TaN-like formation and promoting nitrogen-rich, structurally disordered Ta–N configurations. Rutherford backscattering spectrometry confirms that N-rich films at N₂/Ar ≈ 2 are compositionally uniform, with stoichiometry lying between Ta₃N₅ and Ta₄N₅. Overall, these results establish quantitative deposition–structure–property relationships in nanocrystalline TaN_x thin films and demonstrate that ion-assisted reactive sputtering enables effective tuning of resistivity and optical bandgap. The identified correlations are essential for optimizing electro-optical performance in low-resistivity contacts and liners, as well as high-resistivity blocking and passivation layers for electronic, photonic, and detector applications.