Tuning the electronic structure of 2D materials by strain and external electric field: Case of GeI2 monolayer

Strain and external electric field effect on electronic structure of GeI₂ monolayer has been investigated using first principles calculations. The obtained results indicate that GeI₂ monolayer is an indirect semiconductor with band gap value of 2.188 eV. With biaxial strain, the band gap of considered material increases slightly with compression up to −6% and then it decreases and shows abrupt drop for strain −9% to −12%, whereas it just shows decreasing trend with tensile strain. In case of uniaxial strain, the band gap value increases nearly linearly under the effect of considered strain range. The weak external electric field has no significant effect on the band gap of GeI₂ monolayer, while with E = $\pm$0.6 (eV/Å/e), the band gap decreases considerably as I-6s state in conduction band moves to the lower energy levels.