Ln dependence in Ln₂CuO₄ buffer layers of c-axis in-plane aligned a-axis oriented YBa₂Cu₃O_7-δ thin film growth

Lanthanide (Ln) atom in Ln₂CuO₄ buffer layer dependence of c-axis in-plane aligned a-axis oriented YBa₂Cu₃O_7-δ (YBCO) thin film growth is discussed and preferred orientation growth model of a bc-plane matched growth model is proposed. The c-axis in-plane aligned a-axis oriented YBCO thin films are very attractive from both the researches on the origin of high T_c superconductors and microelectronics device applications. However the c-axis in-plane aligned a-axis oriented films are difficult to grow. We have been proposing Ln₂CuO₄ buffer layers for the c-axis in-plane aligned a-axis oriented YBCO thin film growth. We have examined various Ln atoms in Ln₂CuO₄ buffer layers for the growth of YBCO thin films by pulsed laser deposition. From a lattice matching point of view, a Tb₂CuO₄ buffer layer is the best one for the c-axis in-plane aligned a-axis oriented YBCO thin films. However the result shows that the Nd₂CuO₄ and Tb₂CuO₄ buffer layer causes YBCO thin films with c-axis oriented portion about 35% and 32%, by X-ray diffraction peaks, which is much larger than those on Gd₂CuO₄ buffer layers (7.4%). The most promising Ln atom in Ln₂CuO₄ buffer layers for the growth of the c-axis in-plane aligned a-axis oriented YBCO thin films so far is Gd₂CuO₄ buffer layers or Eu₂CuO₄ buffer layers.