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 WTe_0.6Se_1.4 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.