Minimum energy paths for dislocation nucleation in strained epitaxial layers

Abstract

We study numerically the minimum energy path and energy barriers for dislocation nucleation in a twodimensional atomistic model of strained epitaxial layers on a substrate with lattice misfit. Stress relaxation processes from coherent to incoherent states for different transition paths are determined using saddle point search based on a combination of repulsive potential minimization and the Nudged Elastic Band method. The minimum energy barrier leading to a final state with a single misfit dislocation nucleation is determined. A strong tensile-compressive asymmetry is observed. This asymmetry can be understood in terms of the qualitatively different transition paths for the tensile and compressive strains.

Energetics and atomic mechanisms of dislocation nucleation in strained epitaxial layers

“…Thus the experimentally observed critical thickness can be much larger than the equilibrium value depending on the kinetics of defect nucleation. Our preliminary results 23,24 showed a large variety of relaxation processes, including single dislocation nucleation, multiple dislocations, dislocations with different core structures, and dislocations nucleating on different depth in the film, which can be characterized by their different activation energies and energies of the final incoherent states. In this work, we focus on the nucleation and MEP leading to a final state containing only a single misfit dislocation with core located near the film-substrate interface.…”

“…In the previous work 23 it was found that some features of dislocation nucleation are sensitive to the detailed form of the atomic potentials used. The results presented here are from systematic calculations for different values of cut-off distances for the 5 -8 potential (mϭ8, nϭ5).…”

“…For a correct determination of this barrier, it is important to investigate different minimum-energy paths ͑MEPs͒, 22 from the metastable coherent state to the incoherent state, without assuming a priori any particular form of the intermediate configurations. We have recently carried out such a task which systematically explore the MEPs in the phase space of the system 23,24 based on a combination of the repulsive bias potential 25 and the nudged elastic band methods. 22 In previous work, 23 we considered the case of a relatively large misfit of f ϭϮ8%.…”

“…We have recently carried out such a task which systematically explore the MEPs in the phase space of the system 23,24 based on a combination of the repulsive bias potential 25 and the nudged elastic band methods. 22 In previous work, 23 we considered the case of a relatively large misfit of f ϭϮ8%. We showed that there is indeed a nonzero energy barrier for defect nucleation.…”

“…23. We consider strains in the range f ϭϮ4 -8 %, and intermolecular potentials with different ranges.…”