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, μe of 0.097 cm2 V−1 s−1, conductivity, σ of 0.102 Ω−1 cm−1 and carrier concentration, ne = 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.
Highlights
Electrical transport and IR photoresponse properties of large area VO2(M1) thin films deposited by a simple cost-effective two-step technique
We believe this article is of interest to the intended audience who will fabricate IR photodetectors based on this inexpensive technique
The temperature dependence of Hall mobility (Fig. 7c) shows that it slowly decreases with temperature which can be attributed to scattering of band electrons from acoustic phonons and was consistent with other reports.[4,54,66,67]
Summary
Both physical and chemical, have been used to synthesize VO2 thin lms. Physical methods among others include sputtering,[12] pulsed laser deposition (PLD),[13] molecular beam epitaxy (MBE),[14] and electron beam evaporation.[15] physical methods are expensive and produce thin lms over a small area which does not favor industrial application. As such chemical methods of synthesis have been adopted to synthesize VO2 thin lms over large area due to their low-cost and can be scaled up for industrial production. We believe this article is of interest to the intended audience who will fabricate IR photodetectors based on this inexpensive technique
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