LARGE-AREA EPITAXIAL CEO2 BUFFER LAYERS ON SAPPHIRE SUBSTRATES FOR THE GROWTH OF HIGH-QUALITY YBA2CU3O7 FILMS

It is demonstrated that sapphire with a CeO2 buffer layer can be exploited as an excellent substrate material for growth of large-area YBa2Cu3O7 films. Smooth, epitaxial and crack-free CeO2 buffer layers 130 nm thick were deposited homogeneously on 2 in r-plane sapphire substrates by fully computer-controlled on-axis magnetron sputtering. YBa2Cu3O7 was grown successively on the buffer layer. X-ray diffraction experiments revealed the epitaxial orientations: YBa2Cu3O7(001)//CeO2(001)//Al2O3(1102BAR), with YBa2Cu3O7[110] and [110BAR]//CeO2[100]//Al2O3[1120BAR]. A postdeposition heat treatment improved the crystalline quality and surface morphology of the CeO2 buffer layers, resulting in a channelling minimum yield of less than 2.5% and surface roughness less than 3 nm. No cracks could be detected by scanning electron or atomic force microscopy. The microwave surface resistances of YBa2Cu3O7 films grown on optimized CeO2 buffer layers are comparable with those reported for YBa2Cu3O7 on LaAlO3 wafers.