Improved crystalline quality and electric conductivity in infinite-layer SrFeO₂ films through Sm substitution

We investigated the effect of Sm³⁺ substitution on the crystalline quality and transport properties of "infinite layer" SrFeO₂ epitaxial thin films. Sm-substituted SrFeO₂ (Sr_1-xSm_xFeO₂) films were prepared via a topotactic reaction using CaH₂ on KTaO₃ (KTO) and DyScO₃ (DSO) substrates. The films exhibited metallic behavior with higher conductivity than the undoped ones on both KTO and DSO. The carrier density of the Sm-substituted film was much lower than the Sm³⁺ concentrations, suggesting that the electron carriers generated by Sm were mostly compensated by excess oxide ions residing at the apical sites of Fe. The Sm-substitution also enhanced the crystalline quality of the films, probably because the excess oxide ions stabilized the framework of the infinite layer structure. We found a strong correlation between the conductivity and the crystalline quality in the films, indicating that the conductivity of Sm-substituted SrFeO₂ was dominated by the crystalline quality. Furthermore, a high Hall mobility of 13.5 cm² V^-1 s^-1 was achieved at 300 K in the x = 0.05 film.