Directing Charge\nCarriers and Ferroelectric Domains\nat Lateral Interfaces in van der Waals Heterostructures

Emergent phenomena in traditional ferroelectrics are\nfrequently\nobserved at heterointerfaces. Accessing such functionalities in van\nder Waals ferroelectrics requires the formation of layered heterostructures,\neither vertically stacked (similar to oxide ferroelectrics) or laterally\nstitched (without equivalent in 3D-crystals). Here, we investigate\nlateral heterostructures of the ferroelectric van der Waals semiconductors\nSnSe and SnS. A two-step process produces ultrathin crystals comprising\nan SnSe core laterally joined to an SnS edge-band, as confirmed by\nRaman spectroscopy, transmission electron microscopy (TEM) imaging,\nand electron diffraction. TEM shows a moiré pattern across\nthe SnSe core due to coverage by an ultrathin SnS layer. The ability\nof the lateral interface (IF) to direct excited carriers, probed by\ncathodoluminescence, shows electron transfer over 560 nm diffusion\nlength from the SnS edge-band. Large, thin flakes supporting ferroelectricity\nallow investigating domains and domain wall interactions in uniform\ncrystals and lateral heterostructures. Polarized optical microscopy\nof sub-20 nm flakes consistently shows ⟨110⟩ oriented\nstripe domains with mirror-twin domain walls. Heterostructures adopt\ntwo domain configurations, with domains either constrained to the\nSnSe core or propagating across the entire SnSe–SnS flakes.\nThe combined results demonstrate multifunctional van der Waals heterostructures\nwith high-quality IFs presenting extraordinary opportunities for manipulating\ncarrier flows and ferroelectric domain patterns.