Epitaxial Bi$_{2}$Se$_{3}$ films on Si (111) with atomically sharp interface

Atomically sharp epitaxial growth of Bi$_{2}$Se$_{3}$ films has been achieved on Si (111) substrate with MBE. The growth was self-limited; that is, growth rate was determined completely by Bi flux with excess Se species around. The Bi:Se flux ratio, measured by QCM, was kept $\sim $1:15. Two step growth temperatures were a key to achieving second-phase-free high quality Bi$_{2}$Se$_{3}$ films on Si substrates. With single-step high temperature growth, second phase, presumably SiSe$_{2}$ clusters, was formed at the early stage of growth. On the other hand, with low temperature growth, crystalline quality of the films was poor even if second phase was absent. With low temperature initial growth followed by high temperature growth, second-phase-free atomically sharp interface was obtained between Bi$_{2}$Se$_{3}$ and Si substrate, as verified by RHEED, TEM and XRD. The lattice constant of Bi$_{2}$Se$_{3}$ relaxed to its bulk value during the first quintuple layer based on the RHEED analysis, implying the absence of strain from the substrate. Single-crystalline XRD peaks of Bi$_{2}$Se$_{3}$ were observed in films as thin as 4 QL. TEM shows full epitaxial structure of Bi$_{2}$Se$_{3 }$film down to the first quintuple layer without any second phases. This growth method was used to grow high quality epitaxial Bi$_{2}$Se$_{3}$ films from 3 QL to 3600 QL.