Interface mediated semiconducting to metallic like transition in ultrathin Bi2Se3 films on (100) SrTiO3 grown by molecular beam epitaxy

Abstract

Bismuth selenide (Bi₂Se₃) thin films of nominal thickness ∼10 nm were grown on (100) SrTiO₃ and (100) LaAlO₃ single crystal substrates using molecular beam epitaxy and their charge transport properties were investigated in the temperature range of 1.5 K–300 K. Bi₂Se₃ films deposited on (100) LaAlO₃ exhibit semiconducting behavior, while films prepared on (100) SrTiO₃ exhibited an anomalous semiconductor-to-metal-like transition at 68 K. The low temperature metal like transition is attributed to compressive strains arising due to structural phase transition of SrTiO₃ substrate, which modulate the Bi₂Se₃ grain boundary width and facilitate the electric field assisted tunneling of charge carrier at the grain boundaries. The field assisted tunneling of charge carriers is supported by the inverse square-root field dependence of electrical conductivity.