Carrier generation and compensation mechanism in La2SnO2S3

Abstract

Some Cu-based oxychalcogenides demonstrate robust p-type conductivity, though achieving effective n-type doping in such materials remains a persistent challenge. Among oxychalcogenides, La₂SnO₂S₃ has been proposed as a candidate for an n-type semiconductor because of its dispersive conduction band primarily derived from the Sn-5s states. The experimentally observed n-type conductivity of La₂SnO₂S₃ is, however, limited to a low value, and the underlying atomistic and electronic origins of this behavior remain unresolved. Our systematic first-principles calculations of its point defects using the Heyd–Scuseria–Ernzerhof hybrid functional indicate that the major source of carrier electrons in undoped La₂SnO₂S₃ is unintentionally incorporated H impurities rather than native defects. Moreover, the electrophilic behavior of La₂SnO₂S₃ is unveiled as a pivotal limiting factor for its n-type doping, where carrier electrons are readily trapped around Sn sites in the presence of S vacancies and interstitial H impurities, and even without these defects through self-trapping. This carrier-trapping mechanism is as significant as the electron compensation by Sn vacancies as major acceptor-type native defects. Our synthesis and characterization of polycrystalline La₂SnO₂S₃ confirm its moderate n-type conductivity and the presence of H impurities with a sizable concentration, both of which are in line with the theoretically predicted mechanism. These results clarify crucial limiting factors of n-type conductivity in La₂SnO₂S₃ and provide a fundamental guideline for the design of related n-type oxychalcogenides.