Surface functionalization of GeC monolayer with F and Cl: Electronic and optical properties

In this work, we systematically investigate the electronic and optical properties of surface-functionalized GeC monolayer with F and Cl using density functional theory. Our calculations indicate that the surface functionalization of the GeC with F and C atoms leads to the disruption of the planar structure of the GeC monolayer and the surface-functionalized GeC monolayer has a low-bucking structure. At equilibrium, all four configurations of surface-functionalized GeC monolayer with F and Cl, i.e., F-GeC-F, F-GeC-Cl, Cl-GeC-F, and Cl-GeC-CI, are direct semiconductors. Their band gaps vary from 2.839 eV to 3.175 eV which are calculated using Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. Compared to the other configurations, the formation energy of F-GeC-F is the smallest, -9.097 eV, which implies that this configuration is the most likely to occur. We also used the Mulliken population analysis to estimate the internal charge distribution and transferred charge in the systems. The functionalization of the surface leads to the shifting the first optical gap of the material. The fully chlorination of GeC causes its absorption coefficient to increase significantly, up to 14.912 x 10(4) cm(-1) at the incident light energy of 13.173 eV. Besides, surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. Our calculation results provide detailed information on how to change the electronic and optical properties of monolayer GeC by surface functionalization, which has promising applications in opto-electronic devices.