TlP5: an unexplored direct band gap 2D semiconductor with ultra-high carrier mobility

Two-dimensional materials with an appropriate band gap and high carrier mobility are urgently desired in the field of nanoelectronics. We propose a novel two-dimensional crystal monolayer TlP5, which is dynamically and thermodynamically stable and possesses a direct band gap of 2.02 eV with high carrier mobilities (13 960 cm(2) V-1 s(-1) for electrons and 7560 cm(2) V-1 s(-1) for holes), comparable to that of phosphorene. The band gap value and band characteristics of monolayer TlP5 can be adjusted by biaxial and uniaxial strains, and excellent optical absorption over the visible-light range is predicted. These properties, especially the balanced high mobilities for not only the electrons but also the holes, make monolayer TlP5 an exciting functional material for future applications in nanoelectronics and optoelectronics.