SnSe ₂ Field-Effect Transistor with High On/Off Ratio and Polarity-Switchable Photoconductivity

SnSe ₂ field-effect transistor was fabricated based on exfoliated few-layered SnSe ₂ flake, and its electrical and photoelectric properties have been investigated in detail. With the help of a drop of de-ionized (DI) water, the SnSe ₂ FET can achieve an on/off ratio as high as ~ 10 ⁴ within 1 V bias, which is ever extremely difficult for SnSe ₂ due to its ultrahigh carrier density (10 ¹⁸ /cm ³ ). Moreover, the subthreshold swing and mobility are both improved to ∼ 62 mV/decade and ~ 127 cm ² V ⁻¹ s ⁻¹ at 300 K, which results from the efficient screening by the liquid dielectric gate. Interestingly, the SnSe ₂ FET exhibits a gate bias-dependent photoconductivity, in which a competition between the carrier concentration and the mobility under illumination plays a key role in determining the polarity of photoconductivity.