Tracking optical properties of VOx films to optimize polycrystalline VO2 fabrication

Abstract

In-situ real-time spectroscopic ellipsometry (RTSE) measurements are performed on a growing amorphous vanadium oxide (a-VOx) film to determine the complex dielectric function (ε = ε1 + iε2) spectra, structure, and oxygen content (x) with depth during deposition. VOx with x ∼2 is annealed to produce polycrystalline VO2 and characterized by near-infrared to ultraviolet (0.75–5.9 eV) spectroscopic ellipsometry during heating and cooling from room temperature (RT) to 343 K to RT to track hysteresis effects in the semiconducting-to-metal transition (SMT). Spectra in ε are measured for as-deposited and annealed films prepared with varying deposition parameters to determine the as-deposited film x and verify the SMT. Temperature-dependent IR extended spectroscopic ellipsometry is performed from 0.06 to 0.74 eV to determine the IR ε spectra of polycrystalline VO2 across the SMT. As-deposited amorphous VOx films with x from 1.89 ≤ x ≤ 2.14 transition to polycrystalline VO2 after annealing and exhibit the SMT when heated from RT to 343 K which are verified by substantially increased ε2 magnitude at ≥343 K. By identifying x of a-VOx from ε spectra, a shortened path of qualifying a-VOx films which will crystallize to phase change VO2 is developed.