Preparation and growth mechanism of a-axis-oriented YBa2Cu3O7-δ films by laser metal-organic chemical vapor deposition

Recently we have found a very effective method for controlling the orientation of YBCO films by metal-organic chemical vapor deposition (MOCVD) using uv laser irradiation during deposition onto a MgO(100) substrate. The irradiated part was strongly a-axis-oriented normal to the surface of the substrate for films prepared at 650-700 °C, whereas the unirradiated parts showed c-axis or (110) orientation. This phenomenon occurs not only on MgO(100) substrates but also on other substrates. We obtained a Tc above 81 K on the a-axis oriented part. The critical current density was over 105 A/cm2 at 4.2 K and O T. The surface morphology depends on the laser power density and the repetition rate. A high degree of the a-axis orientation is obtained only by using uv light during deposition of YBCO film. IR or a visible laser causes only surface melting and the destruction of film orientation. We propose that the nuclei for a-axis orientation are formed by the aggregation of Ba caused by uv laser irradiation near the film surface.