Epitaxial growth of YBa2Cu3O7−x thin films on Si(100) with zirconia buffers of varying crystalline quality and structure

Thin epitaxial films of monoclinic pure and cubic yttria-stabilized (YSZ) ZrO2 were deposited onto Si(100) by electron-beam evaporation. The degree of crystalline perfection was controlled by the growth temperature. Epitaxial YBa2Cu3O7−x films were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperature Tc0 of 86–89 K, a critical current density jc of 106 A/cm2 at 77 K, and a channeling minimum yield of 12% was obtained on YSZ buffers showing a minimum yield of 7%. Even a 14-nm-thick YSZ buffer enabled the growth of an YBa2Cu3O7−x film with Tc0 of 86 K and a minimum yield of 12%. With decreasing quality of the YSZ buffer layers the crystalline quality of the superconductor also decreased. The disorder in the YBa2Cu3O7−x films, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa2Cu3O7−x exhibited a pronounced texture with a minimum yield of 72%. The comparatively rough surface of the monoclinic pure ZrO2 severely hampered the c-axis alignment of the YBa2Cu3O7−x, resulting in superconductor films of inferior quality.