SUPERCONDUCTIVITY AND CRYSTALLINITY OF BA2Y1CU3O7-DELTA THIN-FILMS PREPARED BY PULSED LASER DEPOSITION WITH SUBSTRATE BIAS VOLTAGE

Substrate bias voltages were found to be significantly effective in preparing high-quality laser-deposited superconducting Ba2Y1Cu3O7-delta-films at reduced substrate temperatures. The zero-resistance temperature of the biased films, positive bias being more effective than negative, decreased very slightly when the substrate temperature was lowered, whereas that of the unbiased films decreased considerably. In addition, the surface morphology and c-axis orientation have been improved by applying substrate bias voltages. Bias voltages within +/- 500 V hardly affect the composition of the resulting films so that stoichiometric films have been obtained from a stoichiometric target. A time-resolved optical observation revealed that a short time emission, probably being oxygen plasma, occurred in a few mu-s after the laser pulse impingement. The improvement in crystallinity of the resulting films is attributed to this emission. The velocity of emissive species in the plume was determined to be 6 X 10(5) cm/s. Under positive-biased conditions slower components with a velocity of 3 X 10(5) cm/s or less were also observed.