Sulfur-Driven Transition from Vertical to Lateral Growth of 2D SnS–SnS₂ Heterostructures and Their Band Alignments

The rational control of the nucleation and growth kinetics to enable the high-quality growth of two-dimensional (2D) semiconducting metal chalcogenide heterostructures is a key step for the realization of their applications in nanoelectronics and optoelectronics. Here, we report a facile one-step chemical vapor deposition synthesis of 2D SnS–SnS₂ heterostructures with controlled interfacial structures and stacking configurations via tuning S-precursor concentration during the growth. We demonstrate that the change of S-precursor concentration can drive growth transition from vertically stacking SnS₂/SnS van der Waals heterostructures to SnS/SnS₂ core–shell structures with both the lateral and vertical interfaces. Such a transition originates from a delicate competition between the nucleation of SnS and SnS₂. High-resolution spectroscopy measurements and density functional theory (DFT) calculations reveal these SnS–SnS₂ heterostructures with the type-II band alignment, and the measured valence and conduction band offsets are 1.33 and 0.34 eV for vertical SnS₂/SnS heterostructures and 1.43 and 0.54 eV for SnS/SnS₂ core–shell ones, respectively. This work provides an efficient strategy to control the growth of 2D SnS–SnS₂ heterostructures for optoelectronic applications, such as photodetectors and solar cells.