GRAIN-ORIENTATION IN THICK LASER-DEPOSITED Y1BA2CU3O7-DELTA FILMS - ADJUSTMENT OF C-AXIS ORIENTATION

Y1Ba2Cu3O7-delta films with a thickness between 0.5 and 5 mu m were grown on Si covered with an amorphous SiO2 layer, on Zr foils, and on a single-crystalline MgO substrates by KrF laser ablation. The influence of film thickness and substrate temperature on the structure, texture, and microstructure of the as-grown films was investigated by x-ray diffraction and scanning electron microscopy. At an appropriate, substrate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 mu m (critical thickness), followed by a sharp transition to a-axis-oriented growth occurring within about 100 nm. Similar changes could be observed by lowering the substrate temperature by 120 degrees C. Therefore, the hypothesis was propounded that the thickness dependence of the growth orientation of the film is due to a decrease of the surface temperature. To prove this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear increase of the substrate temperature leads to completely c-axis-oriented films up to thicknesses of 5 mu m. A change of the thermal emissivity of the film surface as a possible cooling mechanism is discussed. (C) 1995 American Institute of Physics.