Low-cost VO2(M1) thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture for IR photodetection

Abstract

We report detailed structural, electrical transport and IR photoresponse properties of large area VO₂(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 VO₂ thin films with room temperature Hall mobility, μ_e of 0.097 cm² V⁻¹ s⁻¹, conductivity, σ of 0.102 Ω⁻¹ cm⁻¹ and carrier concentration, n_e = 5.36 × 10¹⁷ cm⁻³. In addition, we fabricated a high photoresponsive IR photodetector based on VO₂(M1) thin films with excellent stability and reproducibility in ambient conditions using a low-cost method. The VO₂(M1) photodetector exhibited high sensitivity, responsivity, quantum efficiency, detectivity and photoconductive gain of 5.18%, 1.54 mA W⁻¹, 0.18%, 3.53 × 10¹⁰ jones and 9.99 × 10³ 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.