Local Structure and Bonding of Transition Metal Dopants in Bi2Se3 Topological Insulator Thin Films

Transition metal (TM) doped topological insnlatofs have been the focus of many recent studies since they exhibit exotic quantum and magneto-electric effects, and offer the prospect of potential applications in Spintronic devices. Here we report a systematic Study of the local electronic and- structural environment using X-ray absorption fine structure (XAFS) in TM (=Cr, Mn, and Fe) doped Bi2Se3 thin films grown by molecular beam epitaxy. Analysis of the TM K-edge XAFS reireals a divalent character for Cr, Mn, arid Fe when substituting Bi in the films, despite the trivalent character of the Bi. All dopants o-Cctipy octahedral siteS, in the Bi2Se3 lattice, Which agrees with stbstitutional incorporation onto the Bi sites. With the incorporation of TM dopants a local structural relaxation of the Bi2Se3 lattice is observed, which strengthens the covalent character of the TM Se bond. The presence of additional phases and interstitial incorporation for the Mn and Fe dopants is also observed, even at low -concentrations.