High-Performance Topological Insulator Bi$_2$Se$_3$ Nanowire Field Effect Transistors*

Single crystal topological insulator Bi$_{2}$Se$_{3}$ nanowires were synthesized by Vapor-Liquid-Solid (VLS) mechanism. Bi$_{2}$Se$_{3}$ NW field-effect transistors were fabricated by using self-alignment method with HfO$_{2}$ as the gate dielectric. Bi$_{2}$Se$_{3}$ NWFETs were measured in vacuum at different temperatures. Excellent MOSFET characteristics were achieved: smooth and well-saturated output characteristics, large On/Off ratio (10$^{7})$, zero Off-state current and good subthreshold slope in transfer characteristics. We have observed linear behavior of the saturation current extracted from the I$_{\mathrm{ds}}$-V$_{\mathrm{ds}}$ curves as a function of the overthreshold voltage (V$_{\mathrm{g}}$-V$_{\mathrm{th}})$, which indicated the main role of the metallic surface conduction at Bi$_{2}$Se$_{3}$ nanowire channel. Both effective mobility and field-effect mobility have been extracted. Very good effective mobility (\textgreater\ 5000 cm$^{2}$V$^{-1}$s$^{-1}$ at 77 K) was obtained under a low gate voltage. From off-state current we calculated the band gap of bulk about 0.33 eV, which is in a good agreement with reported value of 0.35 eV.