A microstructural approach toward the effect of thickness on semiconductor-to-metal transition characteristics of VO2 epilayers

We report the control of semiconductor to metal transition in VO2(010) epilayers integrated with Si{100} substrates buffered with an NiO[111]/YSZ[100] intermediate layer. VO2 epitaxial thin films were grown at different thicknesses varying from 10 to 200 nm using pulsed laser deposition technique. An epitaxial relationship of VO2(010)‖NiO(111)‖ YSZ(001)‖Si(001) and VO2[100]‖NiO[110]‖ YSZ[100]‖Si[100] was established at room temperature. The crystallographic alignment across the VO2/NiO interface changes to VO2(100)‖NiO(111) and VO2[001]‖NiO[110] at the temperature of growth giving rise to a misfit strain of about 33.5% and 3.0% along two orthogonal in-plane orientations. The transition temperature was observed to vary from about 353 to 341 K, the transition amplitude increased by about five orders of magnitude, and the hysteresis decreased to about 3 K, as the thickness of VO2 layers increased from about 10 to 200 nm. These observations were explained based on strain characteristics, overall defect content and grain boundaries, and phenomenological thermodynamic models.