Room-temperature ferroelectricity in van der Waals SnP2S6

Two-dimensional (2D) ferroelectric materials, which possess electrically switchable spontaneous polarization and can be easily integrated with semiconductor technologies, is of utmost importance in the advancement of high-integration low-power nanoelectronics. Despite the experimental discovery of certain 2D ferroelectric materials such as CuInP2S6 and In2Se3, achieving stable ferroelectricity at room temperature in these materials continues to present a significant challenge. Herein, stable ferroelectric order at room temperature in the 2D limit is demonstrated in van der Waals SnP2S6 atom layers, which can be fabricated via mechanical exfoliation of bulk SnP2S6 crystals. Switchable polarization is observed in thin SnP2S6 of ∼7 nm. Importantly, a van der Waals ferroelectric field-effect transistor (Fe-FET) with ferroelectric SnP2S6 as top-gate insulator and p-type WTe0.6Se1.4 as the channel was designed and fabricated successfully, which exhibits a clear clockwise hysteresis loop in transfer characteristics, demonstrating ferroelectric properties of SnP2S6 atomic layers. In addition, a multilayer graphene/SnP2S6/multilayer graphene van der Waals vertical heterostructure phototransistor was also fabricated successfully, exhibiting improved optoelectronic performances with a responsivity (R) of 2.9 A/W and a detectivity (D) of 1.4 × 1012 Jones. Our results show that SnP2S6 is a promising 2D ferroelectric material for ferroelectric-integrated low-power 2D devices.