High quality ultrathin Bi2Se3 films on CaF2 and CaF2/Si by molecular beam epitaxy with a radio frequency cracker cell

Abstract

We report a method to fabricate high quality Bi2Se3 thin films using molecular beam epitaxy with a radio frequency cracker cell as an atomic selenium source. With Se-to-Bi ratios close to exact stoichiometry, optimal layer-by-layer growth of high quality Bi2Se3 thin films with smooth surfaces has been achieved on CaF2(111) substrates and Si(111) substrates with a thin epitaxial CaF2 buffer layer (CaF2/Si). Transport measurements show a characteristic weak-antilocalization magnetoresistance in all the films, with the emergence of a weak-localization contribution in the ultrathin film limit. Quantum oscillations, attributed to the topological surface states have been observed, including in films grown on CaF2/Si.