Janus Ga 2 XTe (X = S, Se) monolayers under hydrostatic pressures: Stability and tunable optoelectronic properties

Abstract

Using DFT+G 0 W 0 +BSE methods, the stability and optoelectronic characteristics of Ga 2 XTe (X = S, Se) monolayers are examined systematically, with particular focus on the effects of hydrostatic pressure. Phonon dispersion spectra validate the dynamical stabilities of the pristine monolayers. G 0 W 0 calculations reveal that these monolayers possess moderate direct bandgaps of ~ 2 eV. Their dynamical stability can be kept under pressures up to 2 (3) GPa for the Ga 2 STe (Ga 2 SeTe), and the bandgap can be significantly modulated under the observed pressures. Though the Bethe-Salpeter equation (BSE), the optical responses of the two Janus monolayers are explored and significant exciton peaks are identified. Interestingly, exerting pressure on the Janus Ga 2 SeTe monolayer significantly modifies the photo-induced transitions, leading to a pronounced red-shift and increased absorption for the visible and near-infrared lights.Additionally, the exciton binding energy in both monolayers decreases significantly with increased pressures, indicating easier exciton dissociation. Our findings suggest that these Janus monolayer materials hold potential as candidates for optoelectronic