Cu₆GeWS₈: A Two-Dimensional Quaternary Sulfide with Direct Bandgap and Ultralow Lattice Thermal Conductivity

Two-dimensional (2D) semiconductors are widely regarded as promising contenders for the next generation of optoelectronics and microelectronics, rendering the development of novel 2D semiconductors a focal point in current research. In this study, our attention is directed towards the non-van der Waals material Cu₆GeWS₈, where we have successfully predicted a stable 2D monolayer, designated as 2D Cu₆GeWS₈. This monolayer exhibits a direct bandgap of 1.709 eV, which maintains its robustness under biaxial strain ranging from −4% to 3%. Remarkably, the monolayer Cu₆GeWS₈ showcases high hole mobility and demonstrates a moderate optical absorption coefficient across the visible and ultraviolet spectra. Notably, our investigation reveals that the monolayer Cu₆GeWS₈ possesses an exceptionally low lattice thermal conductivity of 0.593 W m⁻¹ K⁻¹ at room temperature. These findings underscore the excellent physical characteristics of the predicted monolayer Cu₆GeWS₈, positioning it as a promising candidate for advanced low-dimensional devices.