Effects of strain in heteroepitaxial thin film growth: A ball-spring model

Abstract

Heteroepitaxial growth is one of the promising topics studied in thin film physics. The self-assembled strain islands formed during the growth process are expected to have interesting properties that can be used in optoelectronic devices. Controlling island properties as well as improving island uniformity and ordering are therefore crucial. In this dissertation, we investigate a heteroepitaxial system via computer modeling. A two-dimensional discrete ball and spring model is used in the kinetic Monte Carlo simulations. Our results show that strain at the film-substrate interface creates a bias in the adatom diffusion process which promotes island and pit formations. The pit formation in a limited mobility growth regime is another mechanism to relieve strain in the system. The critical thickness, island size, and number of islands are found to depend on the values of growth conditions. Furthermore, we apply a roughness exponent method normally used in surface growth study to the frustrated antiferromagnetic XY spin model. By mapping spin configurations to film surfaces of a modified SOS growth model, we show that the film roughness and its exponents successfully determine the critical temperature and critical exponents for the chiral symmetry breaking transition in the spin model.