Charge separation in epitaxial SnS/MoS2 vertical heterojunctions grown by low-temperature pulsed MOCVD.

The weak van der Waals bonding between monolayers in layered materials enables fabrication of heterostructures without the constraints of conventional heteroepitaxy. Though many novel heterostructures have been created by mechanical exfoliation and stacking, the direct growth of 2D chalcogenide heterostructures creates new opportunities for large-scale integration. This paper describes the epitaxial growth of layered, p-type tin sulfide (SnS) on n-type molybdenum disulfide (MoS2) by pulsed metal-organic chemical vapor deposition at 180 C. The influence of precursor pulse and purge times on film morphology establish growth conditions that favor layer-by-layer growth of SnS, which is critical for materials with layer-dependent electronic properties. Kelvin probe force microscopy measurements determine a built-in potential as high as 0.95 eV, and under illumination a surface photovoltage is generated, consistent with the expected Type-II band alignment for a multilayer SnS/MoS2 heterostructure. The bottom-up growth of a non-isostructural heterojunction comprising 2D semiconductors expands the combinations of materials available for scalable production of ultrathin devices with field-tunable responses.