Lirong Sun1,2, Faisal Mehmood1, John G. Jones1, Lauren M. Loftus1,2, Tod A. Grusenmeyer1, Ruth Pachter1, Peter R. Stevenson1
1Air Force Research Laboratory, Wright-Paterson Air Force Base, OH
2Azimuth Corporation, a Core4ce LLC, Beavercreek, OH
Niobium-doped zinc oxide (NZO) and niobium oxynitride (NbOxNy) thin films were deposited under ambient temperature using reactive magnetron sputtering, representing optically transparent tailorable conductive films. This work combines experimental fabrication and broadband characterization with spectroscopic ellipsometry to investigate material properties. Experimentally, the niobium (Nb) content was controlled by varying the sputtering power (from 0 to 75 W) on a Nb target while sputtering zinc target simultaneously. The resistivity was tailored by Nb doping content for NZO thin films and by the N2/(O2+Ar) ratio for the NbOxNy thin films. Structural, electrical, and optical properties were characterized over a wide spectral range (210 nm to 30 μm). Increasing the Nb doping concentration resulted in films with improved (002) c-axis crystallinity, lower electrical resistivity reaching a minimum of 2.40 x 10-3 Ω cm, and enhanced near-infrared (NIR) reflectance, all while maintaining high transparency in the visible wavelength region. Density functional theory calculations of NZO revealed that incorporating an oxygen vacancy proximate to the Nb dopant is critical, where this model produced calculated optical property trends in significantly better agreement with our experimental XPS and photoluminescence (PL) results. This combined approach demonstrates that the optoelectronic behavior of NZO is governed by a synergy between the Nb dopant and oxygen deficiency, providing a predictive framework for designing advanced optical coatings. Tuning the resistivity and the extinction coefficient k in the IR region, the optimized NbOxNy thin film is a good material candidate for many applications, such as electrostatic discharge (ESD) materials. The NZO and NbOxNy films were characterized using spectroscopic ellipsometry (SE), x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), four-point probe and photoluminescence (PL).