Strain-induced structural phase transition in GeN monolayer

The recent synthesis of SiP, SiAs, GeP, and GeAs monolayers has brought two-dimensional (2D) group IV-V systems into the limelight. To date, all the fabricated structures of this class belong to the C2/m space group which has a low structural symmetry, while the class could exist in more symmetric phases (i.e., P (3) over bar m1 and P (6) over bar m2). The realization of more symmetric phases can enhance the intrinsic properties of these materials and increase their potential field of usage. In this study, the possibility of a structural phase transition in GeN monolayer by application of mechanical strain is investigated. Based on ab initio simulations, we first confirm the stability of the GeN monolayer in all phases, then demonstrate how a large enough compressive strain (similar to 12%) can transform C2/m into P (3) over bar m1 phase. The results are interpreted by analyzing the geometry, bond order, electron localization functions, and net atomic charges of the structures. Upon transition into the P (3) over bar m1 phase, tensile strength and in-plane stiffness double, while the compressive strength quadruples. On the other hand, the effect of the phase transition on the electronic properties is not substantial and similar band structure profiles with narrowed band gap are obtained. Our study provides insight on how to experimentally achieve the P (3) over bar m1 phase of the GeN monolayer, which is in principle applicable to other group IV-V monolayers under suitable conditions involving the optimization of pressure, temperature, and impurity concentration. These unique features of the GeN monolayer render them ideal candidates for a variety of high technological nanoscale applications.