Superconducting and structural properties of Nd_2-xCe _xCuO_4-y thin films on perovskite and fluorite substrates

High quality epitaxial Nd_2-xCe_xCuO_4-y (NCCO) thin films were fabricated on various substrates by pulsed-laser deposition using N₂O reactive gas. The similarities and dissimilarities of the superconducting and structural properties of NCCO films, on perovskite-type substrates such as LaAlO₃, NdGaO₃, and SrTiO₃ and on a fluorite-type substrate of yttria-stabilized zirconia (YSZ), were investigated systematically as a function of film thickness by transport measurements and structural analysis. A remarkable reduction of T _c was observed when the film was thinner than a critical thickness, which strongly depends on the substrate. The critical thicknesses for which T_c is 80% of T_c max are 1200, 1000, 600, and 450 Å for LaAlO₃, NdGaO₃, SrTiO₃, and YSZ, respectively. YSZ turns out to be the best candidate for the growth of very thin NCCO films among the substrates studied. These results show a strong correlation between the strain and T_c in NCCO thin films and point the way to the fabrication of n-type superconducting electric field devices using ultrathin NCCO films.