Stability and electronic properties of Gex(BN)y monolayers

In this work, we employ ab initio simulations to propose a new class of monolayers with stoichiometry Gex(BN)y. These monolayers belong to a family of 2D materials combining B, N and group IV atoms, such as BxCyNz and SixByNz. We calculated the formation energy for ten atomic arrangements, and found that it increases when the number of BGe and NGe bonds increases, and decreases when the number of BN and GeGe bonds increases. We found that the lowest energy monolayer presented a Ge2BN stoichiometry, and maximized the number of BN and GeGe bonds. This structure also presented mixed sp2 and sp3 bonds and out-of-plane buckling. Moreover, it remained stable in our ab initio molecular dynamics simulations carried out at T = 300 K. The calculated electronic properties revealed that Gex(BN)y monolayers might present conductor or semiconductor behavior, with band gaps ranging from 0.0 to 0.74 eV, depending on atomic arrangement. Tunable values of band gap can be useful in applications. In optoelectronics, for instance, this property might be employed to control absorbed light wavelengths. Our calculations add a new class of monolayers to the increasing library of 2D materials.