STUDY OF YBA2CU3O7-DELTA)(M)/(PRBA2CU3-XGAXO7-DELTA(N) SUPERLATTICES GROWN BY PULSED-LASER DEPOSITION - A COMPARISON BETWEEN A-AXIS-ORIENTED AND C-AXIS-ORIENTED STRUCTURES

Superlattices of YBa2Cu3O7-delta/PrBa2Cu3-xGaxO7-delta (x = 0.2) have been grown by multitarget pulsed-laser deposition on SrTiO3{100} and MgO{100} substrates with their c-axis either normal or parallel to the substrate surface, depending on the growth temperature. At a temperature of 785 degrees C the multilayers are deposited with the c-axis normal to the substrate surface, but with a buffer layer of PrBa2Cu3-xGaxO7, grown at a lower temperature (650 degrees C), the superstructure becomes c-parallel. Secondary-ion mass spectrometry reveals no interdiffusion between Y and Pr, and no diffusion of Ga into the YBa2Cu3O7-delta layer. Nevertheless, the profiles of the c-normal-oriented superlattice are sharper than the c-parallel ones. The 15% minimum yield (chi(min)) measured from RBS in channeling geometry for the c-normal superlattices indicates highly textured growth on SrTiO3, contrary to that which is observed for c-parallel superlattices (chi(min)= 28%) and for c-normal structures grown over an MgO substrate (chi(min) = 50%). The low interface roughness of the c-normal multilayers grown on SrTiO3 is demonstrated by AFM measurements, which give a standard deviation lower than 1.6 nm over 6.25 mu m(2), and also by the streaky RHEED patterns observed at the end of the growth.