Intriguing electronic structures and carrier mobilities of two-dimensional GaN nanosheets: Thickness and surface effects

Two-dimensional GaN nanosheets have emerged as a promising candidate material for the application of low-dimensional optoelectronic devices, but their fundamental electronic structure and intrinsic carrier mobility are extremely sensitive to the phase structure and thickness. Herein, we perform systematic first-principles calculations within hybrid density-functional theory to investigate the thickness and surface effects on electronic properties and carrier mobilities in two-dimensional GaN nanosheets. Our results show that the reduction of thickness leads to a series of phase transitions of pristine GaN nanosheets and surface reconstruction of hydrogenated GaN nanosheets for the minimization of surface dangling bonds. The calculated electronic structures reveal that the band gaps and band-edge states of GaN nanosheets are determined by three competition mechanisms among the quantum confinement effect, surface effect, and Stark effect, resulting in a large band-gap range from 1.32 to 4.35 eV. Owing to the influence of thickness and surface effects, intrinsic carrier mobilities of GaN nanosheets cover a wide range from 400 to 6314 cm(2) V-1 s(-1) for electrons and from 11 to 366 cm(2) V-1 s(-1) for holes, respectively. The findings suggest the possibility to obtain suitable band gap and high carrier mobilities in GaN nanosheets for optoelectronic applications by the control of thickness and phase engineering.