Observation of insulating and metallic-type behavior in Bi2Se3 transistor at room temperature

Recently, topological insulators (Bi2Se3, Bi2Te3 and Sb2Te3) have attracted much attention because of their bulk band gap (0.3 eV) and spin-polarized surface states with conductive massless Dirac Fermions [1]. Interestingly, Bi2Se3 has rhombohedral crystal structure which consists of Se or Bi lattices in stacked manner with the sequence of Se-Bi-Se-Bi-Se. This forms a sheet-like structure in which the adjacent quintuple layers (QL) are bonded by van der Waals forces [2]. According to recent reports, Bi2Se3 has been found to have potential application in field effect transistors (FET), thermoelectric materials, low-power spintronics and opto-electronics. Particularly, Bi2Se3 nanowire FET exhibits superior current-voltage characteristics with a large On/off current ratio, well saturated output current, zero cutoff current, and sharp turn-on voltage [2–5]. These unique properties open up a new consideration of Bi2Se3 as a potential candidate in spintronics and nanoelectronics. There are few reports available on electrical transport studies of Bi2Se3 nanowire transistor [3], epitaxial growth of Bi2Se3 thin films [4], ultra-thin Bi2Se3 thin film [6], and few-layer nano-plates [7]. All these transport studies were investigated in low-temperature environment. When an ultra-thin (thickness ∼3.5 nm) sample with approximately 3 QL investigated, a strong insulating state was observed. However an improved conductance was observed for the samples with thicknesses of 6.5 nm to 14 nm [3]. Yet, up to now, much less attention has paid to investigations on room-temperature transport measurement of Bi2Se3 transistors. The reason behind that, since Bi2Se3 has gapless surface states, it could show surface metallic conduction however the bulk transport conduction cannot be easily identified at room temperature. As reported by H. Zhu et al, by tuning gate electric field at different temperatures, the bulk transport conduction can be isolated from the surface metallic conduction [3]. In this work, we fabricated multi-layer (ML) Bi2Se3 transistor (back-gated) and investigated their characteristics at room temperature. We observed both insulating and metallic-type transport behavior when the device was gate-biased.