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.

1. Hanzawa, Kota, et al. "Material design of green-light-emitting semiconductors: perovskite-type sulfide SrHfS3." Journal of the American Chemical Society 141.13 (2019): 5343-5349.
2. Yu, Zhonghai, et al. "Chalcogenide Perovskite Thin Films with Controlled Phases for Optoelectronics." Advanced Functional Materials 34.7 (2024): 2309514.