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

Abstract

Metal–organic chemical vapor deposition was applied to fabricate YBa2Cu3O7−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).