Dislocation mobility and Peierls stress of c-type screw dislocations in GaN from molecular dynamics

Abstract

Motion of a single c-type screw dislocation, with [0001] Burgers vector, in single crystal GaN is explored using classical molecular dynamics (MD) simulations with both Tersoff and Stillinger-Weber (SW) interatomic potentials. Three different dislocation core structures (full, small void, and open) along two distinct glide planes ((11¯00) and (1¯1¯20)) are studied. The system is sheared by applying opposing forces to atoms near the surface, with interior atoms maintained at a temperature of 1300 K. This results in glide for screw dislocations with a full core structure, with velocities dependent on the choice of interatomic potential. Full core dislocation glide also results in the nucleation of void defects for both potentials. Small void dislocations glide cleanly with no debris using the SW potential, but glide is not observed for the Tersoff potential. The difference between the potentials is most fully demonstrated from the response of open core dislocations in the (1¯1¯20) slip system. For the Tersoff potential, full core screw dislocations are nucleated from the surface of the open core dislocations, while dislocation glide loops are nucleated for the SW potential. The discrepancy in results using the different potentials is discussed, and attributed to the short cut off distance of the Tersoff potential. Finally, a dislocation dipole system is used to calculate the Peierls stress of the {11¯00}〈0001〉 full core screw dislocation, and compared to experimental results.