Tunable electronic and optical properties of Janus Al2M2ClBr (M = O, S) monolayers for UV photodetector applications†

Wide-bandgap 2D materials for UV photodetectors have many advantages, such as flexibility and efficiency. For this reason, the quest for novel 2D semiconductor materials is the primary focus of ongoing research endeavors. In this study, the electronic and optical characteristics of Janus Al₂M₂ClBr (M = O, S) monolayers have been meticulously examined by density functional theory (DFT). It was confirmed that these monolayers exhibit structural robustness for indirect bandgap Al₂O₂ClBr or direct bandgap Al₂S₂ClBr. Moreover, they demonstrate a low effective mass for the photogenerated electrons and holes. The bandgap is notably modulated by strain engineering, whereas the impact of the electric field is minimal. Notably, strong light absorption within the 8 to 12 eV range has been confirmed, with absorption coefficients surpassing 10⁵ cm⁻¹ for Janus Al₂M₂ClBr (M = O, S) monolayers. The optical properties can be finely tuned by strain engineering, although the influence of an electric field on these properties is insignificant. Considering the combination of optical and electrical characteristics, Janus Al₂M₂ClBr (M = O, S) monolayers are promising for UV photodetector applications. As a result, this study provides invaluable theoretical insights into the development of UV photodetectors utilizing Janus monolayers and is poised to significantly enrich the expansion of Janus monolayer materials in the foreseeable future.