Unusual Electronic and Optical Properties of Two-Dimensional Ga 2 O 3 Predicted by Density Functional Theory

β-Ga 2 O 3 is a wide-band-gap semiconductor having a great potential for applications in electronics and optoelectronics. Here, we predict the natural physical properties of atomic monolayer and bilayer Ga 2 O 3 using density functional theory. Although β-Ga 2 O 3 is not a van der Waals material, it is found that two-dimensional (2D) Ga 2 O 3 is stable and can be fabricated by exfoliation. Different from unpassivated 2D Ga 2 O 3, H-passivated 2D Ga 2 O 3 possesses obvious quantum confinement effects. Remarkably, monolayer and bilayer Ga 2 O 3 show larger indirect band gaps (6.42 and 5.54 eV, respectively) and far higher electron mobilities (up to 2684.93 and 24485.47 cm 2 /(V s), respectively) than those of bulk β-Ga 2 O 3 . Moreover, evident variation of band gaps and an indirect-to-direct transition are induced by uniaxial strain. The electron transport in 2D Ga 2 O 3 is anisotropic due to the stronger contribution of O-p z orbitals to the conduction band minimum compared to that of O-p y orbitals. Such characteristics promote the promising application of 2D Ga 2 O 3 in electronic nanodevices. In addition, the electron relaxation time and exciton binding energies of 2D Ga 2 O 3, especially bilayer, are enhanced to 3.77 ps and 0.93 eV, respectively. Moreover, pronounced optical absorbance (up to 10 5 cm –1 ) of 2D Ga 2 O 3 in the solar-blind spectrum enhances its applications in optoelectronic nanodevices.