Hole Carriers Doping Effect on the Metal–Insulator Transition of N‑Incorporated Vanadium Dioxide Thin Films

The coupling of doped charge carriers with the crystal lattice is an efficient route to modulate the phase transition behavior of VO<sub>2</sub>. In the current work, the N-incorporated VO<sub>2</sub> samples are prepared through the low-energy N<sub>2</sub><sup>+</sup> ion sputtering of the crystalline VO<sub>2</sub> films. The critical temperatures (<i>T</i><sub>c</sub>) of the metal–insulator transition (MIT) process are observed to decrease with a value of ∼18 °C for VO<sub>1.9</sub>N<sub>0.1</sub> and VO<sub>1.87</sub>N<sub>0.13</sub> samples. The effects of nitrogen incorporation on the MIT depression have been revealed by the electronic structural characterizations via the X-ray adsorption near-edge structure (XANES) spectroscopy and photon electronic spectroscopy (SRPES). The implanted nitrogen atoms are identified to coordinate with the V<sup>4+</sup> ions at the substituent position of oxygen atoms. The p-type dopant provides the hole carriers into the d<sub>∥</sub> sub-bands, resulting in the attenuation of the interaction within V–V dimer and the narrowing of the energy band gap in M1 phase. Both aspects unanimously facilitate the depression of the MIT temperature in N-incorporated VO<sub>2</sub>.