Indium selenide monolayer: strain-enhanced optoelectronic response and dielectric environment-tunable 2D exciton features

Electronic and optical performances of the β-InSe monolayer (ML) are considerably boosted by tuning the corresponding band energies through lattice in-plane compressive strain engineering. First principles calculations show an indirect-direct gap transition with a large bandgap size. The crossover is due to different responses of the near-gap state energies with respect to strain. This is explained by the variation of In-Se bond length, the bond nature of near-band-edge electronic orbital and of the momentum angular contribution versus in-plane compressive strain. The effective masses of charge carriers are also found to be highly modulated and significantly light at the indirect-direct-gap transition. The tuned optical response of the resulting direct-gap ML β-InSe is evaluated versus applied energy to infer the allowed optical transitions, dielectric constants, semiconductor-metal behavior and refractive index. The environmental dielectric engineering of exciton behavior of the resulting direct-gap ML β-InSe is handled within the effective mass Wannier-Mott model and is expected to be important. Our results highlight the increase of binding energy and red-shifted exciton energy with decreasing screening substrates, resulting in a stable exciton at room temperature. The intensity and energy of the ground-state exciton emission are expected to be strongly influenced under substrate screening effect. According to our findings, the direct-gap ML β-InSe assures tremendous 2D optoelectronic and nanoelectronic merits that could overcome several limitations of unstrained ML β-InSe.