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 (Cu 2 S) monolayer, denoted δ-Cu 2 S, with both novel electronic properties and superior oxidation resistance. We find that both monolayer and bilayer δ-Cu 2 S have much lower formation energy than the known β-Cu 2 S phase. Given that β-Cu 2 S sheets have been recently synthesized in the laboratory (Adv. Mater.2016, 28, 8271), the higher stability of δ-Cu 2 S than that of β-Cu 2 S sheets suggests a high possibility of experimental realization of δ-Cu 2 S. Stability analysis indicates that δ-Cu 2 S is dynamically and thermally stable. Notably, δ-Cu 2 S exhibits superior oxidation resistance, due to the high activation energy of 1.98 eV for the chemisorption of O 2 on δ-Cu 2 S. On its electronic properties, δ-Cu 2 S 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 β-Cu 2 S bilayer. The marked difference between the electron and hole mobilities of δ-Cu 2 S suggests easy separation of electrons and holes for solar energy conversion. Combination of these novel properties makes δ-Cu 2 S a promising 2D material for future applications in electronics and optoelectronics with high thermal and chemical stability.
ASJC Scopus subject areas
- Materials Science(all)