Reactive sputtering of SnS thin films using sulfur plasma and a metallic Tin target: achieving stoichiometry and...

Tin sulfide (SnS) is a promising earth-abundant and non-toxic material for photovoltaic applications; however, its practical use has been hindered by difficulties in achieving both stoichiometric composition and large grain sizes in thin films-factors critical for improving device performance. This study presents a unique strategy for fabricating high-quality SnS thin films with controlled stoichiometry and micron-scale grains using a metallic tin target and sulfur plasma (S-plasma). Unlike conventional approaches that rely on toxic H₂S gas, this method employs a S-plasma to enhance sulfur reactivity and mitigate sulfur deficiencies during film deposition. By optimizing the balance between the sputtering conditions of the Sn target and the supply conditions of the S-plasma, dense single-phase SnS thin films with micron-scale grain sizes were achieved at a substrate temperature of 300 °C, achieving an in-plane Hall mobility of 13 cm² V^-1 s^-1. Furthermore, crystalline SnS thin films were fabricated even on a room-temperature substrate, enabling potential applications in flexible devices with heat-sensitive substrates. These results indicate that reactive sputtering with S-plasma is an efficient and safer route to high-performance SnS thin films, overcoming long-standing challenges in composition control and grain growth.