Mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi

We have examined the mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi. We consider the role of the transition from group-V-rich to group-III-rich conditions, i.e., the stoichiometry threshold, in the presence of Bi. For As-rich GaAsBi growth, Bi acts as a surfactant, leading to the formation of droplet-free GaAsBi films. For films within 10% of the stoichiometric GaAsBi growth regime, surface Ga droplets are observed. However, for Ga-rich GaAsBi growth, Bi acts as an anti-surfactant, inducing Ga-Bi droplet formation. We propose a growth mechanism based upon the growth-rate-dependence of the stoichiometry threshold for GaAsBi.