Unusual Electronic and Optical Properties of Two-Dimensional Ga2O3 Predicted by Density Functional Theory

beta-Ga2O3 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 Ga2O3 using density functional theory. Although beta-Ga2O3 is not a van der Waals material, it is found that two-dimensional (2D) Ga2O3 is stable and can be fabricated by exfoliation. Different from unpassivated 2D Ga2O3, H-passivated 2D Ga2O3 possesses obvious quantum confinement effects. Remarkably, monolayer and bilayer Ga2O3 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 beta-Ga2O3. Moreover, evident variation of band gaps and an indirect-to-direct transition are induced by uniaxial strain. The electron transport in 2D Ga2O3 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 Ga2O3 in electronic nanodevices. In addition, the electron relaxation time and exciton binding energies of 2D Ga2O3, 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 Ga2O3 in the solar-blind spectrum enhances its applications in optoelectronic nanodevices.