Structure and Morphology Controlled Growth of Bismuth Selenide Films with Tunable Transport Properties on H-Passivated Si(111) by Molecular Beam Epitaxy

The structures of bismuth selenides are formed by periodic or nonperiodic stacking of Bi2Se3 quintuple layers and Bi2 bilayers, which can be represented by a general formalism of BixSey (x, y > 0). In this work, we report the controlled growth and morphology characteristics of BixSey films on Si(111) by the coevaporation of Bi and Se using molecular beam epitaxy, as well as the basic transport properties. The higher growth temperature limit for achieving stoichiometric Bi4Se3 films of a single-crystalline structure and smooth surface morphology is found to be as low as 350 K. At this temperature, a series of BixSey films with a continuous composition evolution from Bi4Se3 to Bi2Se3 is obtained by precisely adjusting the Bi:Se flux ratios. All BixSey films grown on flat Si(111) share a similar pyramid morphology, owing to a spiral growth mode. By contrast, Bi4Se3 films grown on a vicinal Si(111) surface, for instance, exhibit lower twinning defects due to a step-confined in-plane anisotropic growth mode. Hall effect measurements show that a metal-to-semiconductor-to-metal phase transition occurs in BixSey films with increasing Se composition.