Epitaxial growth of MOCVD-derived YBCO films by modulation of Cu(tmhd)₂ concentration

Metal–organic chemical vapor deposition was applied to fabricate YBa₂Cu₃O_7−δ (YBCO) films on single-crystal LaAlO₃ (001) substrates for its high deposition rate, easy adjustment on film composition, and low requirement on vacuum apparatus. The effects of Cu(tmhd)₂ concentration in the precursor on the properties of YBCO films were systematically investigated. X-ray diffraction (XRD) reveals that the mole ratio of Cu/Ba in the precursor from 0.77 to 0.97 is helpful to improve the crystallization and out-of-plane orientation of YBCO films; however, it hardly affects the in-plane texture. Scanning electron microscope (SEM) shows the dense, crack-free but rough surface, on which there are Cu–O and Ba–Cu–O outgrowths identified by energy-dispersive spectrometer (EDS). As the mole ratio of Cu/Ba increasing, the average size of Ba–Cu–O precipitates keeps increasing and the film composition becomes inhomogeneous at the mole ratio of Cu/Ba of 0.97. The 250 nm thick YBCO film prepared at the mole ratio of Cu/Ba of 0.91 shows the critical current density (J _c) of 4.0 MA·cm⁻² (77 K, 0 T).