Electronic structures and anisotropic carrier mobilities of monolayer ternary metal iodides MLaI₅(M=Mg, Ca, Sr, Ba)

Exploiting two-dimensional (2D) materials with natural band gaps and anisotropic quasi-one-dimensional (quasi-1D) carrier transport character is essential in high-performance nanoscale transistors and photodetectors. Herein, the stabilities, electronic structures and carrier mobilities of 2D monolayer ternary metal iodides MLaI₅(M = Mg, Ca, Sr, Ba) have been explored by utilizing first-principles calculations combined with numerical calculations. It is found that exfoliating MLaI₅monolayers are feasible owing to low cleavage energy of 0.19-0.21 J m^-2and MLaI₅monolayers are thermodynamically stable based on phonon spectra. MLaI₅monolayers are semiconductors with band gaps ranging from 2.08 eV for MgLaI₅to 2.51 eV for BaLaI₅. The carrier mobility is reasonably examined considering both acoustic deformation potential scattering and polar optical phonon scattering mechanisms. All MLaI₅monolayers demonstrate superior anisotropic and quasi-1D carrier transport character due to the striped structures. In particular, the anisotropic ratios of electron and hole mobilities along different directions reach hundreds and tens for MLaI₅monolayers, respectively. Thus, the effective electron-hole spatial separation could be actually achieved. Moreover, the absolute locations of band edges of MLaI₅monolayers have been aligned. These results would provide fundamental insights for MLaI₅monolayers applying in nano-electronic and optoelectronic devices.