Kinetic Monte Carlo simulation of strained heteroepitaxy in three dimensions

Abstract

Morphological evolution of strained heteroepitaxial films is studied using a kinetic Monte Carlo method in three dimensions. The film-substrate structure is modeled by a cubic lattice of balls and springs representing atoms and elastic interactions. Atomic surface diffusion is simulated using an activated hopping algorithm. The hopping barrier depends on both atomic coordination and elastic stress so that poorly coordinated or highly stressed atoms hop preferentially. The elastic stress is efficiently computed repeatedly during every stage in the surface evolution using a Green's function method and a super-particle coarsening approximation. Applying our algorithms, films of area up to 64 by 64 atoms are studied. We have simulated annealing of initially flat films. At relatively high temperature, the film surface develops ripples, which later grow into three dimensional (3D) islands. At lower temperature, two dimensional (2D) islands and 3D pits are observed. The pits subsequently develop into grooves. Simulations of film deposition are also conducted. At low deposition rate, isolated 3D islands are observed. At higher deposition rate comparable to the corresponding surface roughening rate, morphologies similar to those from annealing are observed.