Locking of Screw Dislocations in Silicon due to Core Structure Transformation

The activity of screw dislocations dominates the brittle deformation regime at low temperatures in silicon (Si) and other semiconductors, while the mechanisms behind it remain not fully understood. Here, we employ molecular dynamics and nudged elastic band simulations to examine the energy barriers and pathways of the transformations between various core structures of the 1/2 <110> screw dislocation and the stress barriers of their glides in Si. We find that the high energy core structures transform into the most stable configuration through thermal activation under relatively low temperature and stress-free conditions. Intriguingly, the stress barrier to activate the glide of the stable core is, however, much higher than the metastable cases. Consequently, the movement of the screw dislocation in Si could be essentially locked through the energetically favorable transformation of the core structure, which may account for the brittle behavior of Si at low temperatures. Our results suggest that suppression of the dislocation core transitions may be an effective approach to improve the plastic deformation of Si.