Epitaxial growth of topological insulator Bi_2Se_3 film on Si(111) with atomically sharp interface

摘要

Atomically sharp epitaxial growth of Bi_2Se_3 films is achieved on Si(lll) substrate with molecular beam epitaxy. Two-step growth process is found to be a key to achieve interfacial-layer-free epitaxial Bi_2Se_3 films on Si substrates. With a single-step high temperature growth, second phase dusters are formed at an early stage. On the other hand, with low temperature growth, the film tends to be disordered even in the absence of a second phase. With a low temperature initial growth followed by a high temperature growth, second-phase-free atomically sharp interface is obtained between Bi_2Se_3 and Si substrate, as verified by reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and X-ray diffraction. The lattice constant of Bi_2Se_3 is observed to relax to its bulk value during the first quintuple layer according to RHEED analysis, implying the absence of strain from the substrate. TEM shows a fully epitaxial structure of Bi_2Se_3 film down to the first quintuple layer without any second phase or an amorphous layer.