Two-step synthesis and characterization of vertically stacked SnS-WS₂ and SnS-MoS₂ p-n heterojunctions

We demonstrate the synthesis of unique heterostructures consisting of SnS and WS₂ (or SnS and MoS₂) by two-step chemical vapor deposition (CVD). After the first CVD growth of triangular WS₂ (MoS₂) grains, the second CVD step was performed to grow square SnS grains on the same substrate. We found that these SnS grains can be grown at very low temperature with the substrate temperature of 200 °C. Most of the SnS grains nucleated from the side edges of WS₂ (MoS₂) grains, resulting in the formation of partly stacked heterostructures with a large overlapping area. The SnS grains showed doped p-type transfer character with a hole mobility of 15 cm² V^-1 s^-1, while the WS₂ and MoS₂ grains displayed n-type character with a high on/off ratio of >10⁶. The SnS-WS₂ and SnS-MoS₂ heterostructures exhibited clear rectifying behavior, signifying the formation of p-n junctions at their interfaces. This heterostructure growth combined with the low temperature SnS growth will provide a promising means to exploit two-dimensional heterostructures by avoiding possible damage to the first material.