Enhanced phase transition and infrared photoresponse characteristics in VO2(M1) thin films synthesized by DC reactive sputtering on different substrates

Abstract

VO₂ is a material with high potential for low-cost optoelectronic, switching and energy saving devices. This work presents the synthesis of smooth high-quality VO₂(M1) thin films on quartz (VO₂-Qu) and c-sapphire (VO₂-Saph) substrates by two-step DC reactive sputtering with enhanced semiconductor-to-metal transition (SMT) and infrared (IR) photoresponse characteristics. Phase formation and purity were confirmed by XRD and Raman measurements. Morphological analysis by AFM and SEM revealed the nanosized nature of the films with a surface roughness of 37 ± 0.5 nm and 48 ± 1 nm for VO₂-Qu and VO₂-Saph thin films respectively. The VO₂-Qu and VO₂-Saph thin films exhibit thermally activated SMT temperature (T_SMT) of 71 °C and 68 °C with resistance change of 4 and 5 orders of magnitude respectively. Infrared (λ = 1064 nm and 1550 nm) photoresponse characteristics of the low-cost photodetector fabricated based on the synthesized VO₂(M1) films increase with a decrease in film roughness. The responsivity increases in the order VO₂-Qu (14.02 mA W⁻¹) > VO₂-Saph (11.1₂ mA W⁻¹) under an IR (λ = 1064 nm, 250 mW cm⁻²) laser at a bias voltage of 10 V. The higher energy (λ = 1064 nm) laser yields an enhanced photoresponse compared to the lower energy (λ = 1550 nm) laser owing to the efficient generation of charge carriers with a higher laser energy. This work provides a way for the large-scale synthesis of high-quality VO₂(M1) thin films for various device applications.