Tin disulfide (SnS2) thin-film field-effect transistors

Tin disulfide (SnS₂) is a layered metal dichalcogenide semiconductor [1]. Its crystal structure and many of its electrical, optical and catalytic properties are similar to those of molybdenum disulfide (MoS₂) [2] which has received significant attention due to the large electron mobilities of over 500 cm²/Vs that have been measured in monolayer MoS₂ field-effect transistors (FETs) [3]. A potential advantage of SnS₂ over MoS₂ is its larger bandgap (2.3 eV for bulk SnS₂ [1], compared to 1.2 eV for bulk MoS₂ [2]), which may translate into smaller leakage currents and larger on/off ratios in FETs, especially when the channel length is small and the applied drain-source voltage is large. Recently, Song et al. reported an electron mobility of 50 cm²/Vs for FETs based on mechanically exfoliated SnS₂ monolayers [4]. These monolayer FETs showed a subthreshold swing of 10 V/decade and a promising on/off ratio of 10⁵, but similar to many metal dichalcogenide FETs reported in the literature, this large on/off ratio was obtained only when the applied drain-source voltage was very small (0.01 V). In addition, the FETs had a negative threshold voltage. However, for many applications, such as active-matrix displays and low-power logic circuits, positive threshold voltages and large on/off ratios at large drain-source voltages are more desirable. Here we demonstrate FETs based on mechanically exfoliated SnS₂ multilayers with a thickness of several hundred nanometers that have relatively small field-effect mobilities (0.04 cm²/Vs), but provide a steep subthreshold swing (4 V/decade) and a large on/off ratio (10⁶) even when the applied drain-source voltages are quite large (10 V).