Semiconducting M₂X (M = Cu, Ag, Au; X = S, Se, Te) monolayers: A broad range of band gaps and high carrier mobilities

Two-dimensional semiconductors (2DSCs) with appropriate band gaps and high mobilities are highly desired for future-generation electronic and optoelectronic applications. Here, using first-principles calculations, we report a novel class of 2DSCs, group-11-chalcogenide monolayers (M₂X, M = Cu, Ag, Au; X = S, Se, Te), featuring with a broad range of energy band gaps and high carrier mobilities. Their energy band gaps extend from 0.49 to 3.76 eV at a hybrid density functional level, covering from ultraviolet-A, visible light to near-infrared region, which are crucial for broadband photoresponse. Significantly, the calculated room-temperature carrier mobilities of the M₂X monolayers are as high as thousands of cm²·V^-1·s^-1. Particularly, the carrier mobilities of η-Au₂Se and ε-Au₂Te are up to 10⁴ cm²·V^-1·s^-1, which is very attracitive for electronic devices. Benefitting from the broad range of energy band gaps and superior carrier mobilities, the group-11-chalcogenide M₂X monolayers are promising candidates for future-generation nanoelectronics and optoelectronics.