Sb doping effect on transport behavior in the topological insulator Bi2Se3

Abstract

Bismuth selenide (Bi2Se3) is a good topological insulator (TI) with its surface band Dirac point inside the bulk bandgap. However, Bi2Se3 films grown by molecular beam epitaxy (MBE) often require tuning of Fermi level near the Dirac point for optimal proximity effect with magnetic or superconducting materials. In this study, we achieve the control of the Fermi level in MBE-grown Bi2Se3 thin films by antimony (Sb) doping and systematically investigate the transport properties of these Bi2-xSbxSe3 films with different doping concentrations. Excellent topological surface conduction is attained, and weak antilocalization is observed in all Sb-doped Bi2Se3 films. While the carrier mobility shows no dependence on the Sb concentrations, indicating that the phonon scattering dominates over the impurity scattering from Sb dopants, the coherence length varies significantly with the Sb doping level at low temperatures (< 30 K), highlighting the non-negligible electron-electron interactions in the low temperature regime. Furthermore, EuS/Bi2-xSbxSe3 heterostructures are fabricated to explore proximity-induced ferromagnetism in the TI surface states. However, the long-range magnetic order is not formed in the TI surface states under our growth conditions. Our results emphasize the critical role of interface quality for realizing exchange coupling. This work offers new insights into the interplay of disorder, decoherence, and scattering mechanisms in Sb-doped Bi2Se3 thin films, providing guidance for the future study of the proximity effect in heterostructures involving Sb-doped Bi2Se3.