Non-stoichiometry in SnS: How it affects thin-film morphology and electrical properties

Tin sulfide (SnS) has garnered much attention as a promising material for various applications, including solar cells and thermoelectric devices, owing to its favorable optical and electronic properties and the abundant and nontoxic nature of its constituent elements. Herein, we investigated the effect of non-stoichiometry on the morphology and electrical properties of SnS thin films. Using a unique sputtering technique with a sulfur plasma supply, SnS films with precise sulfur content control, [S]/([Sn] + [S]) (xS) ranging from 0.47 to 0.51, were fabricated. Systematic characterization revealed that non-stoichiometry on the S-rich side led to a marked increase in the carrier density of p-type conduction, which was attributed to the formation of intrinsic acceptor-type defects. In contrast, non-stoichiometry on the S-poor side hardly affects the p-type electrical properties, apparently because of the self-compensation between the intrinsic acceptor- and donor-type defects. In addition, non-stoichiometry has been identified as the cause of thin-film morphological changes, with non-stoichiometric films exhibiting rough and porous surfaces. Achieving a stoichiometric composition results in smooth and dense thin-film morphologies, which are crucial for optimizing SnS thin films for device applications. These findings underscore the importance of compositional control for tailoring the morphology and electrical behavior of SnS, paving the way for more efficient SnS-based devices.