First principles prediction of XI (X=Be, Mg) monolayer semiconductors: Modified Becke-Johnson approach

In this work, we propose two new Alkaline-Iodine XI (X = Be, Mg) two dimensional structures namely BeI, and MgI monolayer with the hexagonal crystal structure (space groups of 187-P6m2) is theoretically predicted. Our estimating on their stability determines that both BeI and MgI monolayers have excellent stabilities and they may be experimentally produced. The analysis of the band structures of these two monolayers provides semiconductor nature with strain tunable indirect band gaps of 2.23/2.83, 1.59/1.93 eV calculated by PBE/mBJ functional for BeI, and MgI monolayers respectively. Our investigation on their optical properties predicts that they indicate almost no absorption and show very low reflectivity in the visible region of the electromagnetic spectra, in case they have significant absorption and reflection properties in UV region. The presented results reveal that XI (X = Be, Mg) monolayer semiconductors are good candidate for practical nano-electronic applications.