The mechanism of plastic deformation in intact and irradiated GaN during indentation: A molecular dynamics study

A series of molecular dynamics simulations are carried out to study the mechanical properties of GaN. Firstly, indentation simulations are performed on the c-plane and m-plane GaN. Combined with the evolution of defects in the GaN substrate, the anisotropic mechanical responses are discussed in detail. It is found that plastic deformation in an intact c-plane GaN starts with generation and extension of planar defects. These planar defects eventually gather together and transform into a disordered region with a growing size. While for the m-plane GaN, the deformation during an indentation is dominated by the nucleation and propagation of dislocations. Secondly, the irradiation effect on the mechanical properties of GaN is investigated. Irradiated models, which subjected to different irradiation dose ranging from 5 eV/atom to 50 eV/atom, are adopted in the indentation simulations. A hardening phenomenon is found for the low-dose irradiated m-plane GaN, and the hardnesses of c-plane and m-plane GaN decrease significantly when the irradiation dose exceeds 30 eV/atom. In addition, the indentations conducted on the irradiated models induce dramatically different deformation behaviors. In particular, with the increase of irradiation dose, the deformation mechanism transforms from the plastic activities on slip systems to local rearrangements of atoms in disordered regions.