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

Abstract

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 Bi_xSe_y (x, y > 0). In this work, we report the controlled growth and morphology characteristics of Bi_xSe_y 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 Bi_xSe_y films with a continuous composition evolution from Bi₄Se₃ to Bi₂Se₃ is obtained by precisely adjusting the Bi:Se flux ratios. All Bi_xSe_y 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 Bi_xSe_y films with increasing Se composition.