Growth of multiple WS2/SnS layered semiconductor heterojunctions

Abstract

Both WS₂ and SnS are 2-dimensional, van der Waals semiconductors, but with different crystal structures. Heteroepitaxy of these materials was investigated by growing 3 alternating layers of each of these materials using atomic layer deposition on 5 cm × 5 cm substrates. Initially, WS₂ and SnS films were grown and characterized separately. Back-gated transistors of WS₂ displayed n-type behavior with an effective mobility of 12 cm² V⁻¹ s⁻¹, whereas SnS transistors showed a p-type conductivity with a hole mobility of 818 cm² V⁻¹ s⁻¹. All mobility measurements were performed at room temperature. As expected, the heterostructure displayed an ambipolar behavior with a slightly higher electron mobility than that of WS₂ transistors, but with a significantly reduced hole mobility. The reason for this drop can be explained with transmission electron micrographs that show the striation direction of the SnS layers is perpendicular to that of the WS₂ with a 15 degree twist, hence the holes have to pass through van der Waals layers that results in drop of their mobility.