Al-Doping-Induced VO₂ (B) Phase in VO₂ (M) Toward Smart Optical Thin Films with Modulated ΔT_vis and ΔT_c

Vanadium dioxide (VO₂) thin films are among the promising candidates for smart optical materials and energy-saving devices with a metal–insulator transition (MIT) near room temperature. The modulation of hysteresis width (ΔT_c) and optical characteristics of the solar spectral band (T_sol) during the MIT of vanadium oxides used for thermochromic devices is still challenging. In this article, we describe Al-doped VO₂ thin films with modulated visible spectral band (T_vis) and ΔT_c. The control of the Al/V ratio and Al-doping-induced VO₂ (B) phases in VO₂ is achieved by combining atomic layer deposition and post-annealing processes. With increasing Al/V ratio, the content of VO₂ (B) phases increases in VO₂ (M). ΔT_vis, ΔT_c, and Al-doping-induced VO₂ (B) phases are found to be dependent on the aluminum content in thin films. ΔT_vis up to 21.18% and ΔT_c down to 3.3 K for Al-doped VO₂ may be attributed to the coordinated interaction of both Al doping and the VO₂ (B) phases in the VO₂ matrix during MIT. These modulations may allow an understanding of the essential physics behind the MIT of doped VO₂ and thus fabrication of smart optical sensors, energy-saving devices, and even ultrafast Mott transistors.