Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

Requisite to growing stoichiometric perovskite thin films of the solid-solution A'_1-xA_xBO₃ by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO₃ and ABO₃, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La_1-xSr_xVO₃, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'_1-xA_xBO₃.