Low-cost VO 2 (M1) thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture for IR photodetection.

We report detailed structural, electrical transport and IR photoresponse properties of large area VO 2 (M1) thin films deposited by a simple cost-effective two-step technique. Phase purity was confirmed by XRD and Raman spectroscopy studies. The high quality of the films was further established by a phase change from low temperature monoclinic phase to high temperature tetragonal rutile phase at 68 °C from temperature dependent Raman studies. An optical band gap of 0.75 eV was estimated from UV-visible spectroscopy. FTIR studies showed 60% reflectance change at λ = 7.7 μm from low reflectivity at low temperature to high reflectivity at high temperature in a transition temperature of 68 °C. Electrical characterization showed a first order transition of the films with a resistance change of four orders of magnitude and TCR of -3.3% K -1 at 30 °C. Hall-effect measurements revealed the n-type nature of VO 2 thin films with room temperature Hall mobility, μ e of 0.097 cm 2 V -1 s -1 , conductivity, σ of 0.102 Ω -1 cm -1 and carrier concentration, n e = 5.36 × 10 17 cm -3 . In addition, we fabricated a high photoresponsive IR photodetector based on VO 2 (M1) thin films with excellent stability and reproducibility in ambient conditions using a low-cost method. The VO 2 (M1) photodetector exhibited high sensitivity, responsivity, quantum efficiency, detectivity and photoconductive gain of 5.18%, 1.54 mA W -1 , 0.18%, 3.53 × 10 10 jones and 9.99 × 10 3 respectively upon illumination with a 1064 nm laser at a power density of 200 mW cm -2 and 10 V bias voltage at room temperature.