Precise control of the phase-transition temperature of VO2 from 70 to -35 °C for tunable optics

Abstract: We demonstrate the combination of metal doping and ion bombardment as a hybrid technique to precisely engineer the insulator-to-metal transition (IMT) properties of vanadium dioxide (VO$_2$) films. This approach enables (i) setting the phase-transition temperature ($T_c$) from $-35$ to $70$ {\deg}C, (ii) near-zero hysteresis in highly doped and irradiated films, and (iii) robust optical contrast across a broad range of doping and irradiation conditions, down to $T_c = -35$ {\deg}C. While previous work has focused on engineering the IMT via one of metal doping or ion irradiation, our hybrid method utilizes both. In doing so, we address several lingering challenges in VO$_2$ engineering, including the trade-off between $T_c$ reduction and optical contrast, and limitations in the achievable value of T$_c$. Strain$-T_c$ correlation from XRD and Raman measurements suggests a common mechanism behind doping- and irradiation-induced $T_c$ reduction. The ability to reduce the $T_c$ and hysteresis of VO$_2$ while maintaining large optical contrast will extend the functionality of VO$_2$-based optical and optoelectronic devices, including detectors, limiters, and modulators.