TlP ₅: 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 TlP ₅ , which is dynamically and thermodynamically stable and possesses a direct band gap of 2.02 eV with high carrier mobilities (13960 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 TlP ₅ 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 TlP ₅ an exciting functional material for future applications in nanoelectronics and optoelectronics.