Light Polarization Sensitive Transistor Action in the van der Waals ferroelectric 4H-SnS2
Van der Waals (vdW) ferroelectric semiconductors provide a unique platform for exploring the interplay between spontaneous polarization, electronic transport, ion migration, and photocarrier generation at the nanoscale. Here, we establish a room-temperature ferroelectric state in SnS2 and its sensitivity to structural polytype by directly contrasting the centrosymmetric 2H-phase with the polar 4H-phase. Raman spectroscopy distinguishes the 2H and 4H polymorphs of SnS2 through their characteristic phonon fingerprints. Piezoresponse force microscopy confirms room-temperature ferroelectricity in the 4H phase, while the 2H phase exhibits no ferroelectric response. The built-in polarization in a three-terminal transistor device of the 4H-SnS2 is modulated significantly by electrostatic gating and on exposure to linear and circularly polarized light. This device reveals polarization-controlled output characteristics with distinct gate-voltage induced hysteretic response and thermally activated carrier transport, confirming p-type semiconducting behavior strongly coupled to ferroelectric polarization. The photoresponse likewise exhibits polarization-assisted carrier separation, sublinear power-law scaling, a nonmonotonic temperature response correlated with the characteristic Raman modes, ferroelectric hysteresis, and a pronounced dependence on the circular and linear polarization states of the incident laser beam. These results establish 4H-SnS2 as a promising material system for polarization-driven electronic and optoelectronic technologies, including nonvolatile memory and photoferroelectric functionalities.