Copper(i) sulfide: a two-dimensional semiconductor with superior oxidation resistance and high carrier mobility

Two-dimensional (2D) semiconductors with suitable direct band gaps, high carrier mobility, and excellent open-air stability are especially desirable for material applications. Herein, we show theoretical evidence of a new phase of a copper(i) sulfide (Cu2S) monolayer, denoted -Cu2S, with both novel electronic properties and superior oxidation resistance. We find that both monolayer and bilayer -Cu2S have much lower formation energy than the known -Cu2S phase. Given that -Cu2S sheets have been recently synthesized in the laboratory (Adv. Mater.2016, 28, 8271), the higher stability of -Cu2S than that of -Cu2S sheets suggests a high possibility of experimental realization of -Cu2S. Stability analysis indicates that -Cu2S is dynamically and thermally stable. Notably, -Cu2S exhibits superior oxidation resistance, due to the high activation energy of 1.98 eV for the chemisorption of O-2 on -Cu2S. On its electronic properties, -Cu2S is a semiconductor with a modest direct band gap (1.26 eV) and an ultrahigh electron mobility of up to 6880 cm(2) V-1 s(-1), about 27 times that (246 cm(2) V-1 s(-1)) of the -Cu2S bilayer. The marked difference between the electron and hole mobilities of -Cu2S suggests easy separation of electrons and holes for solar energy conversion. Combination of these novel properties makes -Cu2S a promising 2D material for future applications in electronics and optoelectronics with high thermal and chemical stability.