Crystalline α-Sm2S3 nanowires: Structure and optical properties of an unusual intrinsically degenerate semiconductor

Highlights: ► Developed a rapid synthetic method to generate thin films of α-Sm2S3 nanowires. ► Calculated the electronic structure of α-Sm2S3 by density functional theory. ► Predicted that α-Sm2S3 is an intrinsically degenerate p-type semiconductor. ► Found that the gap in the band states of α-Sm2S3 could be engineered to 1.3 eV via sulfur vacancy. -- Abstract: The lanthanide sulfides have long been a promising class of semiconductors because of their infrared-to-visible range band gaps and excellent thermoelectric properties. However, their applications have been limited due to their time consuming conventional synthetic processes and the lack of sufficient understanding of their electronic properties. To address these shortcomings, here we report a rapid, chemical vapor deposition route which results in thin films of crystalline α-phase samarium sesquisulfide (α-Sm2S3) nanowires within a few hours, rather than the typical 4–7 days required in previous synthetic processes. In addition, density functional theory was, for the first time, utilized to calculate the electronic band structure of α-Sm2S3 in order to shed insight into the interpretation of their UV–Vis absorption spectrum. We found that the theoretical direct gap in the band states of α-Sm2S3 is 1.7 eV. Computation results suggest that this gap can be tuned to a solar optimal ∼1.3 eV via systematic sulfur vacancy sites engineered into the crystal structure. Most significantly, the degenerate semiconductor-like behavior long observed in lanthanide sulfide samples have been shown to be present even in the ideal α-Sm2S3 structure, suggesting that the observed heavily p-type behavior is an unusual intrinsic property of the material resulting from the Fermi level being located significantly below the optically active 1.7 eV band edge