Two Janus Ga 2 STe monolayers and their electronic, optical, and photocatalytic properties.

Recently, two-dimensional Janus materials have attracted increasing interest due to their unique structure and novel properties. Based on density-functional and many-body perturbation theories ( i.e. DFT + G 0 W 0 + BSE methods), the electronic, optical, and photocatalytic properties of Janus Ga 2 STe monolayers with two configurations are explored systematically. It is found that the two Janus Ga 2 STe monolayers exhibit high dynamical and thermal stabilities and have desirable direct gaps of about 2 eV at the G 0 W 0 level. Their optical absorption spectra are dominated by the enhanced excitonic effects, in which bright bound excitons possess moderate binding energies of about 0.6 eV. Most interestingly, Janus Ga 2 STe monolayers show high light absorption coefficients (larger than 10 6 cm -1 ) in the visible light region, effective spatial separation of photoexcited carriers, and suitable band edge positions, which make them potential candidates for photoelectronic and photocatalytic devices. These observed findings enrich the deep understanding of the properties of Janus Ga 2 STe monolayers.