Stable Oxygen Incorporation in Superconducting TaN: An Experimental and Theoretical Assessment

Oxide formation in superconducting TaN thin films is analyzed through experimental measurements and computational simulations. TaN was synthesized in an ultrahigh vacuum (UHV) system by reactive pulsed laser deposition and characterized in situ by X-ray photoelectron spectroscopy; it was also characterized ex situ by X-ray diffraction, transmission electron microscopy, and the four-point probe method. Despite being grown in an UHV chamber with a base pressure of 5 × 10^-9 Torr, TaN contains a significant amount of oxygen (up to 20 at. %) attributed to residual gases containing O atoms. Several TaN_1- O models, with different amounts of O atoms incorporated into N sites, were simulated using ab initio calculations to assess the feasibility of oxide formation. Thermodynamic stability analysis reveals that TaN_1- O stability increases with oxygen addition, indicating that its incorporation is thermodynamically favorable. The oxygen-impurified TaN exhibits a face-centered cubic structure and is a superconductor (R = 0 Ω) at 2.99 K. The results discussed here highlight the importance of considering stable oxygen impurities when studying superconductivity in TaN films. The formation of TaN_1- O regions in the compound may be key to understanding the variation in critical temperature reported in the literature.