Epitaxial growth of YBa₂Cu₃O_7-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 YBa₂Cu₃O_7-x films were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperature T_c0 of 86-89 K, a critical current density j_c 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 YBa₂Cu₃O_7-x film with T_c0 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 YBa₂Cu₃O_7-x films, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa₂Cu₃O_7-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 YBa ₂Cu₃O_7-x, resulting in superconductor films of inferior quality.