Lowering symmetry around N-cluster by breaking Ga-N bond in GaAsN

The symmetry around the structure of N clusters aligned to (110) direction in GaAsN with dilute N is expected to be lowered by breaking a Ga-N bond. By the bond breaking, the position of the N atom deviates from the lattice point to relax local stresses. On the other hand, the tetrahedral symmetry around As atoms prefers to be maintained. The lowering of the symmetry around N is essentially caused by the two factors: the difference between the bond lengths of Ga-N and Ga-As, and the lattice matching to GaAs. The smallest number of N atoms in the N-cluster that has breaking Ga-N bonds is roughly estimated to be three with the help of total energy and structural relaxation calculations by using the density functional theory and pseudopotential method.