Monte carlo simulations of step flow in molecular beam epitaxy grown surfaces

Abstract

Molecular beam epitaxy growth on vicinal substrates are studied using the Monte Carlo simulation technique. A vicinal surface consists of equal-width flat terraces of different height separated by step edges. It is a type of substrate widely used in thin film fabrication. It is well-known that high quality films can be obtained when the growth is in step flow mode. The aim of this work is to find growth conditions that lead to step flow growth on vicinal substrates, and to study statistical properties of the grown films. Two discrete growth models, the Das Sarma-Tamborenea and the Family models, are used for this task. Both models have been well-studied for limited mobility cases. A slight modification, adding long surface diffusion length noise reduction technique, is made so atomic mobility can be varied in these models. Since the atomic mobility depends directly on the growth temperature, varying the diffusion length in the study means effects of the growth temperature can be investigated. Quantities of interest are morphology, temporal correlation function, persistence probability and survival probability distribution. The simulated results show that the step flow mode begins when the growth temperature is high enough so that the atomic diffusion length is approximately half of the terrace width. Atomic processes found during the step flow mode are deposition at the step edges and diffusion on the terraces. Both persistence and survival probability distributions decrease with growth time. The persistence exponent, which is the rate that the probability decreases, is small when the growth is