Molecular Dynamics Simulations of the Thermally and Stress-Activated Glide of a < 0001 >{1(1)over-bar00} Screw Dislocation in AlN

The low-temperature plasticity of aluminum nitride (AlN) is determined by the interaction between edge and screw dislocations. However, the motion of screw dislocations and their glide mechanisms have not been evaluated. In this study, the motion of a < 0001 >{1 (1) over bar 00} screw dislocation in a single crystal of AlN is explored by molecular dynamics simulations using LAMMPS software with the Stillinger-Weber (SW) potential. Four modes of thermally activated motion are observed under different conditions of temperature and stress: double kinks, Shockley partials, self-pinning, and debris and dislocation loops. The mobilities of a < 0001 >{1 (1) over bar 00} screw dislocation and a 1/3 < 11 (2) over bar0 >{1 (1) over bar 00} edge dislocation are compared under various conditions. Our results show that the mobilities of the < 0001 >{1 (1) over bar 00} screw and 1/3 < 11 (2) over bar0 >{1 (1) over bar 00} edge dislocations are quite low at T < 600 K. The < 0001 >{1<(1)over bar>00} screw dislocation moves faster at 900 < T < 1500 K and seems less dependent on the temperature than does the 1/3 < 11 (2) over bar0 >{1 (1) over bar 00} edge dislocation at 1200 < T < 2200 K. However, the opposite phenomenon is observed at higher temperatures. The mobility of the < 0001 >{1 (1) over bar 00} screw dislocation is slightly lower than that of the 1/3 < 11 (2) over bar0 >{1 (1) over bar 00} edge dislocation at T > 1800 K, although the mobility difference can reach several orders of magnitude at 900 < T < 1200 K due to different Peierls barriers.