Exploring epsilon near zero response and enhanced properties in tungsten Oxynitride: A DFT and experimental study

The current study investigated the effects of nitrogen doping on the structural, electronic, optical, and thermoelectric properties of WO₃ for optoelectronic applications. The analysis was conducted using both density functional theory and experimental studies on thin films synthesized via magnetron sputtering. Nitrogen incorporation reduced the band gap, induced a direct transition, and enhanced charge mobility. The density of state spectra confirmed strong p-d hybridization, with W-d and O-p orbitals playing a key role. Thermoelectric analysis showed a significant increase in electrical conductivity from 0.93 × 10¹⁹ (S/m·s) in undoped WO₃ to 46 × 10¹⁹ (S/m·s) in composition having maximum nitrogen content, as calculated using BoltzTraP under constant relaxation time approximation. However, excessive doping increased thermal conductivity and phonon scattering, reducing thermoelectric efficiency. X-ray diffraction analysis revealed the cubic phase, while optical analysis recorded notable changes in the refractive index and absorption coefficient, along with the emergence of epsilon-near-zero behavior in the NIR-visible range, which highlights its potential for advanced optoelectronic applications.