Stress relaxation and misfit dislocation nucleation in the growth of misfitting films: A molecular dynamics simulation study

Abstract

The low-temperature growth and relaxation of misfitting films are analyzed on the basis of two-dimensional molecular dynamics simulations using Lennard-Jones potentials. The temporal evolution of the surface morphology and the mechanisms for misfit dislocation nucleation and stress relaxation are monitored. Pseudomorphic film growth is observed up to a critical thickness. In some cases, the formation of voids within the film relaxes some of the stress. At the critical thickness, dislocations nucleate and relax most of the misfit. The critical thickness increases with decreasing lattice mismatch and depends on the sign of the misfit. The critical thickness of compressively strained films is smaller than that of films with the same magnitude of misfit, but in tension. The mechanism of dislocation nucleation is different in tension and compression and, in all cases, is associated with the roughness of the film surface. In the compressive misfit case, dislocations nucleate by squeezing-out an atom at the base of surface depressions. In the tensile misfit case, however, the nucleation of misfit dislocations involves the concerted motion of a relatively large number of atoms, leading to insertion of an extra lattice ͑plane͒ row into an already continuous film. These results show that the critical thickness depends intimately on the film morphology which, in turn, is determined as an integral part of the film growth process.

Enhanced Incorporation of P into Tensile-Strained GaAs1-yPyLayers Grown by Metal-Organic Vapor Phase Epitaxy at Very Low Temperatures

“…This difference in relaxation behavior is rationalized in terms of the local anharmonic atomic potentials and difference in the dislocation nucleation mechanism for the two different strain states. 35 Fig . 4 shows the calculated critical thickness for crack formation 31 and for dislocation formation, 35 as well as our experimentally deduced layer thickness versus the misfit.…”

“…The blue and red dotted lines are calculated by energy minimization method with LennardJones potential, while the black dotted line by numerically solving the energyequilibrium model by Matthews and Blakeslee. 35 The solid and hollow data points represent the experimentally measured layer thickness for crack-free and cracked samples, respectively.…”

“…) unless CC License in place (see abstract 31 and for dislocation formation 35 versus misfit. The blue and red dotted lines are calculated by energy minimization method with LennardJones potential, while the black dotted line by numerically solving the energyequilibrium model by Matthews and Blakeslee.…”

Energetics and atomic mechanisms of dislocation nucleation in strained epitaxial layers

“…18 -20 Thus, atomistic studies are important for a detailed understanding and determination of the possible mechanisms for defect nucleation in epitaxial films. Although the importance of kinetic factors in real experiments has already been emphasized 11 and also investigated in numerical simulations of atomistic models of the growth process, 20 a direct determination of the transition path and corresponding energy barrier for misfit dislocation nucleation from an epitaxial film has been much less explored, and they often require assumptions on the particular structure of the intermediate configuration. 21 The actual stress relaxation processes starting from the epitaxial coherent state can occur along many different transition paths.…”

Dislocations and morphological instabilities: Continuum modeling of misfitting heteroepitaxial films

“…It is theoretically challenging to address both plasticity and buckling in this nonequilibrium process; the former involves singular contributions to the strain, while the latter constitutes a freeboundary-value problem. A molecular dynamics study of Dong et al 13 addressed both aspects of the process and found a qualitative coupling between buckling and dislocation nucleation; the relaxation of misfit strain by dislocations occurred inside grooves, which came about by the relaxation of strain by buckling. Schwarz 14 studied misfit dislocation lines in three-dimensional static films in a quasiequilibrium framework.…”