Room temperature tunability of Mo-doped VO₂ nanofilms across semiconductor to metal phase transition

The phase transition temperature (T_t) across semiconductor-to-metal transition (SMT) of the vanadium dioxide (VO₂) thin films can be tuned to room temperature either by reducing the grain size of crystallites to nanoscale or by doping them with molybdenum (Mo⁶⁺) ions. In this work, the combined response of these effects (quantum size effect and doping mechanism) has been demonstrated by studying the structural and electrical transport properties of low concentration (0, 1, 3 and 5%) Mo⁶⁺-doped VO₂ nanofilms across SMT. Room temperature value of T_t = 303.7 K was achieved for Mo⁶⁺-doped VO₂ nanofilms as compared to 333.2 K of pristine VO₂ nanofilms and against 340 K of bulk VO₂ thin films. A systematic analysis of charge carrier mobility (μ), Seebeck coefficient (s) and charge carrier concentration (n) was performed for the first time to the best knowledge of the authors. Decrease in μ and increase in s were observed across SMT with increase in doping percentage of Mo⁶⁺-ions. n increased by 1 to 4 orders of magnitude across SMT for the samples which contributed almost entirely for the resistance change. Resistance ratio (R_s/R_M) and hysteresis width (ΔH) diminished whereas hysteresis sharpness (ΔT) escalated across SMT with the increase of Mo⁺⁶-ions. - Highlights: • Mo-doped VO₂ nanofilms have been fabricated on sapphire substrates by solgel method. • Room temperature phase transition was achieved by effects of nanosize and Mo-doping. • Carrier concentration increased up to 4 orders of magnitude across phase transition. • Seebeck coefficient increased and mobility decreased with increase in Mo-doping.