Large-area epitaxial CeO 2 buffer layers on sapphire substrates for the growth of high quality YBa 2Cu 3O 7 films

Abstract

It is demonstrated that sapphire with a CeO 2 buffer layer can be exploited as an excellent substrate material for growth of large-area YBa 2Cu 3O 7 films. Smooth, epitaxial and crack-free CeO 2 buffer layers 130 nm thick were deposited homogeneously on 2 in r-plane sapphire substrates by fully computer-controlled on-axis magnetron sputtering. YBa 2Cu 3O 7 was grown successively on the buffer layer. X-ray diffraction experiments revealed the epitaxial orientations: YBa 2Cu 3O 7(001)//CeO 2(001)//Al 2O 3(1 102) , with YBa 2Cu 3O 7[110] and [1 10]//CeO 2[100]// Al 2O 3[11 20] . A postdeposition heat treatment improved the crystalline quality and surface morphology of the CeO 2 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 YBa 2Cu 3O 7 films grown on optimized CeO 2 buffer layers are comparable with those reported for YBa 2Cu 3O 7 on LaAlO 3 wafers.