Abstract
In this work, VO2 thin films were deposited on Si wafers (onto (100) surface) by DC magnetron sputtering under different cathode bias voltages. The effects of substrate biasing on the structural and optical properties were investigated. The results show that the metal–insulator transition (MIT) temperature of VO2 thin films can be increased up to 14 K by applying a cathode bias voltage, compared to deposition conditions without any bias. The decrease in the transition efficiency and increase in the transition temperature are attributed to the enlarged grain size, increased defects, and the residual stress in the VO2 thin films induced by biasing. The optical transmittance measurements for different thickness films indicate an attenuation coefficient of 3.1 × 107 m−1 at 2000 nm or an extinction coefficient of 4.9 in the metal phase. The optical transmittance vs wavelength characteristics point to an indirect bandgap of 0.6 ± 0.5 eV and significant scattering in the bulk and/or at the interface.
Highlights
Vanadium dioxide (VO2 ) has been widely studied in recent years because of its ability to undergo a reversible metal–insulator transition (MIT) at around 68 ◦ C, from a low-temperature insulating M-phase to a high-temperature metallic R phase [1]
In order to study the effect of substrate biasing, we have used single-phase VO2 thin films deposited under different substrate bias voltages
The present work clearly shows that applying substrate biasing can modify the microstructure and optical properties of VO2 thin films deposited by magnetron sputtering
Summary
Vanadium dioxide (VO2 ) has been widely studied in recent years because of its ability to undergo a reversible metal–insulator transition (MIT) at around 68 ◦ C, from a low-temperature insulating M-phase (monoclinic) to a high-temperature metallic R phase (rutile) [1]. This reversible transition makes VO2 an excellent material for ultrafast optical switches, smart windows, Mott transistors, strain and gas sensors, actuators, and so forth [2,3,4,5]. The effects of strain, grain size, stoichiometry, substrate temperature, and substrate material have been extensively studied and optimized to achieve good crystallinity with a higher optical transmittance and a higher near-IR switching contrast [8,9,10,11,12,13,14,15]
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