PREPARATION AND GROWTH-MECHANISM OF A-AXIS-ORIENTED YBA2CU3O7-DELTA 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-degrees-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 T(c) above 81 K on the a-axis oriented part. The critical current density was over 10(5) A/cm2 at 4.2 K and 0 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.