Surface functionalization modulates the structural and optoelectronic properties of two-dimensional Ga2O3

Fabricating low-dimensional ultra-wide-bandgap β-Ga2O3 has been regarded as a promising approach to optimize the performance of β-GaO Ga2O3–based optoelectronics. Controlling the surface-dangling bonds of low-dimensional Ga2O3 is crucial for the performance modulation. Here, the structural stability and optoelectronic properties of two-dimensional (2D) Ga2O3 tuned by halogen passivation are comparatively investigated by density functional theory. No matter how full passivation and semipassivation, both chlorine and fluorine passivation can change the indirect bandgap into direct bandgap for 2D Ga2O3 because of the higher energy of bonding orbital for Ga-halogen bond than that of Ga–O bond. Moreover, surface chlorine passivation promotes the formation of p-type 2D Ga2O3 with reduced bandgap because chlorine passivation supplies electron to Ga2O3, while fluorine passivation introduces some subconduction bands into the enlarged bandgap because of the π∗ antibonding between the F-py and O-py orbitals. In addition, just chlorine passivation can simultaneously improve the electron and hole mobility of 2D Ga2O3, while opposite characters are observed for fluorine-passivated 2D Ga2O3. The hole mobility of chlorine semipassivated p-type monolayer Ga2O3 along b direction increases to 3913.52 cm2V−1s−1. Moreover, surface chlorine passivation not only enhances the absorption in the ultravisible region but also extends the absorption range of 2D Ga2O3 from the ultravisible to visible region. Note that the fluorine-passivated 2D Ga2O3 has more stability than the chlorine-passivated one. This work deeply reveals the effect of surface halogen passivation and provides useful guidance for realizing high-performance p-type Ga2O3 optoelectronics.