Modeling and Simulation of Strained Heteroepitaxial Growth

Abstract

We introduce an off-lattice model with continuous particle distances and pair-potential interactions which allows for the efficient simulation of strained heteroepitaxial growth by means of kinetic Monte Carlo (KMC) simulations. We discuss in detail the application of our model to the simulation of three important strain relaxation mechanisms: First, the formation of misfit dislocations in strained adsorbate films is investigated. We find a power-law misfit dependence of the critical layer thickness, in agreement with various experimental studies. Second, we study the self-assembled island formation on a thin adsorbate wetting-layer (Stranski-Krastanov growth). We show that an increased diffusion barrier on the substrate is a possible kinetic reason for the formation of a stable wetting-layer. The formation of islands can be ascribed to a partial relaxation of adsorbate material which affects the diffusion barriers for adsorbate particles. The dependence of island size and density on misfit, temperature and particle flux is in good qualitative agreement with metal-organic vapor phase epitaxy experiments. Finally, we consider surface alloying as strain relaxation mechanism in multi-component systems. Equilibrium simulations show that the competition between binding and strain energy yields regular stripe patterns. Under non-equilibrium conditions we find pattern formation as well as the experimentally observed island ramification. The comparison with a lattice gas model shows that the stripe formation can solely be due to kinetic effects but the misfit is essential for the ramification and stabilization of the surface structures.