Janus Ga₂XTe (X = S, Se) monolayers under hydrostatic pressures: stability and tunable optoelectronic properties

Using DFT + G₀W₀ + BSE methods, the stability and optoelectronic characteristics of Ga₂XTe (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. G₀W₀ calculations reveal that these monolayers exhibit moderate direct bandgaps of ∼2 eV. Their dynamical stability can be maintained under pressures up to 2 (3) GPa for Ga₂STe (Ga₂SeTe), and the bandgap can be significantly modulated under the observed pressures. Using 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 Ga₂SeTe 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 have potential as candidates for optoelectronic nanodevices.