Density functional theory-based strain engineering of electronic optical and thermoelectric properties of A₂OX (A = Ga, in and X = S, Se) monolayers

The realization of Janus monolayers presents an exciting opportunity to disrupt structural symmetry, opening up novel avenues in the realm of layered materials. While several ternary systems, comprising the group-III monochalcogenides, has been proposed for this purpose, the impact of oxygen interaction on the electronic, thermoelectric and optical characteristics of gallium and indium monochalcogenides has been observed. Interestingly, the concept of incorporating oxygen as a third element in ternary systems has not yet been explored extensively. Here we embark on the design and exploration of 2D A₂OX (A = Ga, In and X = S, Se) monolayer through first-principles calculations. Our investigation includes the analysis of electronic band structure, optical and thermoelectric properties, revealing that Ga₂OS, Ga₂OSe and In₂OS exhibit direct band nature. However, In₂OSe is found to be metallic in unstrained condition. Moreover, the band gap in these materials can be fine-tuned through the application of tensile or compressive strain. Additionally, our analysis suggests strong optical absorption within the visible, and/or ultraviolet regions, depending on the specific system under consideration. Our findings reveal that Ga₂OS and In₂OS monolayers elevated power factors with application of tensile strain, rendering them as compelling candidates for applications in thermoelectric devices.