Interplay between Growth Mechanism, Materials Chemistry, and Band Gap Characteristics in Sputtered Thin Films of Chalcogenide Perovskite BaZrS3

The prototypical chalcogenide perovskite BaZrS3, with its direct band gap, exceptionally strong light-harvesting ability and good carrier transport properties, provides fundamental prerequisites for a promising photovoltaic material. This inspired synthesis of BaZrS3 in the form of thin films, using sputtering and rapid thermal processing, aimed at device fabrication for future optoelectronic applications. Using a combination of long- and short-range structural information from x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD), we have elucidated how, starting from a random network of Ba, Zr, S atoms, thermal treatment induces crystallization and growth of BaZrS3 and explained its impact on observed PL properties. We also provide an electronic structure description and confirm the surface material chemistry using a combination of depth-dependent Photoelectron Spectroscopy (PES) using Hard X-ray (HAXPES) and traditional Al Kα radiation. From the knowledge of the optical band gap of BaZrS3 thin films, synthesized at an optimal temperature of 900°C, and our estimation of the valence band edge position with respect to the Fermi level, one may conclude that these semiconductor films are intrinsic in nature with a slight n-type character. A detailed understanding of the growth mechanism and electronic structure of BaZrS3 thin films helps pave the way for their use in photovoltaics.