Effect of Sr doping on structure, morphology, and transport properties of Bi2Se3 epitaxial thin films

We report molecular beam epitaxy growth of Sr-doped Bi2Se3 films on the (111) BaF2 substrate, aimed to realize unusual superconducting properties inherent to SrxBi2Se3 single crystals. Despite the wide range of the compositions, we do not achieve superconductivity. To explore the reason for this, we study the structural, morphological, and electronic properties of the films and compare them with the corresponding properties of the single crystals. The dependence of the c-lattice constant in the films on the Sr content appears to be more than an order of magnitude stronger than that in the crystals. Correspondingly, all other properties also differ substantially, indicating that Sr atoms get different positions in lattices. We argue that these structural discrepancies arise from essential differences in growth conditions. Our research calls for more detailed structural studies and novel growth approaches for the design of superconducting SrxBi2Se3 thin films.