Synthesis of High Quality SrHfS₃ Thin Films via Sputtering and Two-Step Annealing

SrHfS₃, in its distorted perovskite structure, has been identified as a direct bandgap semiconductor with a bandgap of approximately 2.4 eV, exhibiting strong green photoluminescence^[1][2]. This material's high stability and defect tolerance make it a promising candidate for applications such as LEDs. In this study, we report the synthesis of SrHfS₃ thin films using magnetron sputtering with elemental metal targets, followed by CS₂ sulfurization. A significant challenge in sputter synthesis using metal targets is the evaporation of Sr during high-temperature processing, leading to off-stoichiometry and deteriorating film quality. Under normal processing conditions, the off-stoichiometry can even prevent the formation of the distorted perovskite phase. To address this challenge, we employed a two-step annealing method. The first step involves low-temperature annealing in CS₂ to allow interdiffusion of metal cations. The reaction with CS₂ leads to the formation of amorphous SrHfS_x. The bonding of Sr cation with sulfur prevents the evaporation of Sr and ensures cation stoichiometry. The second step involves high-temperature annealing to form SrHfS₃ and crystallizes it into the distorted perovskite structure. This approach enhances the quality of the films and is beneficial for device fabrication.<br/><br/>1. Hanzawa, Kota, et al. "Material design of green-light-emitting semiconductors: perovskite-type sulfide SrHfS3." <i>Journal of the American Chemical Society</i> 141.13 (2019): 5343-5349.<br/>2. Yu, Zhonghai, et al. "Chalcogenide Perovskite Thin Films with Controlled Phases for Optoelectronics." <i>Advanced Functional Materials</i> 34.7 (2024): 2309514.