Owing to their dramatic ultrafast reversible metal insulator transition (MIT), vanadium dioxide (VO2) thin films are of significant interest for numerous potential applications, such as ultrafast electro-optical switching devices, Mott field-effect transistors, and optical waveguides [1-3]. Since THz transmittance dramatically changes across this first-order structural phase transition, it indicates good application potential for THz device. In general, VO2 film has a high phase transition temperature and a wide hysteresis width, especially on silicon substrates, which restrict the development of VO2-based devices. For practical application the MIT properties have to be tailored. In this work, We have deposited undoped, Hf doped VO2 and Hf-Nb co-doped VO2 thin film on high-purity single-crystal Si substrates by DC reactive magnetron sputtering method and investigated their switching properties at THz range. Finally, the excellent combined switching properties were obtained by Hf and Nb co-doping. In particular, the Hf-Nb codoped VO2 film exhibits a small hysteresis width around 5.8 °C, a low phase transition temperature down to 47.1 °C and a high THz transmission modulation depth of 84%, which is promising for THz modulation applications . This work provides a feasible solution to the design and fabrication of VO2 films with suitable MIT properties for THz device.
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 M.N. Ferdous Hoque, G. Karaoglan-Bebek, M. Holtz, A.A. Bernussi, Z. Fan, High performance spatial light modulators for terahertz applications, Opt. Communications, 350 (2015) 309-314.
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 X. Wu, Z. Wu, C. Ji, H. Zhang, Y. Su, Z. Huang, J. Gou, X. Wei, J. Wang, Y. Jiang, THz Transmittance and Electrical Properties Tuning across IMT in Vanadium Dioxide Films by Al Doping, ACS Appl Mater Interfaces, 8 (2016) 11842-11850.