Epitaxial Non c-Axis Twin-Free Bi₂Sr₂CaCu₂O_8+δ Thin Films for Future THz Devices

Thin films of (117) Bi₂Sr₂Ca₂CuO_8+δ (Bi-2212) were grown by Molecular Organic Chemical Vapor Deposition (MOCVD) on (110) SrTiO₃ and (110) LaAlO₃ substrates. Substrates were vicinal with off angles up to 20°. Films are 3D epitaxial and X-ray diffraction φ-ψ scans demonstrate that, while the films grown on a flat substrate are composed of twinned grains, the films on vicinal substrate are twin-free. A higher quality is obtained if growth is performed at two temperatures: Growth starts at 550⁻600 °C and continues at 700⁻750 °C. The twin-free film grown by the two-temperature method shows a zero-resistance critical temperature of 37 and 32 K when the measuring current is applied in-plane parallel and perpendicular to [001] direction of the substrate. Twin-free non c-axis thin films are promising for fabrication of novel planar THz devices.