Structure and morphology of Ge nanowires on Si (001): Importance of the Ge islands on the growth direction and twin formation

Understanding and controlling the structural properties of Ge nanowires are important for their current and future use in technological applications. In this study, the initial stages of the heteroepitaxial growth of Ge nanowires on Si(001) via the Au catalyzed vapor-liquid-solid (VLS) method are investigated. We observe a Ge island located at the base of each nanowire. We propose that these islands are formed by the VLS mechanism and initiate the nanowire growth. Analysis of the islands morphology helps to explain the < 011 > growth direction commonly observed for Ge nanowires. Moreover, our observations provide an insight into the formation of twins that propagate along the growth direction. (C) 2015 AIP Publishing LLC.