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 gr own 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 d iffraction and scanning electron microscopy. At an appropriate, substr ate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 mu m (critical thic kness), followed by a sharp transition to a-axis-oriented growth occur ring within about 100 nm. Similar changes could be observed by lowerin g the substrate temperature by 120 degrees C. Therefore, the hypothesi s was propounded that the thickness dependence of the growth orientati on of the film is due to a decrease of the surface temperature. To pro ve this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear incre ase of the substrate temperature leads to completely c-axis-oriented f ilms up to thicknesses of 5 mu m. A change of the thermal emissivity o f the film surface as a possible cooling mechanism is discussed. (C) 1 995 American Institute of Physics.