Effect of processing geometry in oxygen incorporation and in situ formation of YBa₂Cu₃O₇ superconducting thin films by pulsed laser evaporation technique

In situ formation of YBa₂ Cu₃ O₇ superconducting thin films by the pulsed laser evaporation technique is critically dependent on the processing conditions (substrate temperature, oxygen partial pressure, subsequent annealing, etc.) and on the deposition setup, including the nozzle geometry required for the incorporation of oxygen. We have studied the recovery of the superconducting properties as a function of location of the oxygen jet relative to a fixed substrate-target setup at a substrate temperature of 550°C and an oxygen partial pressure of 200 mTorr. Several experiments were performed with the oxygen jet directed on the target and/or on the substrate. During the deposition process, a dc bias voltage of +300 V was applied on an interposing ring, which has resulted in formation of superconducting thin films at a low temperature of 500°C. Excellent superconducting properties with the T_c zero of 88 K were obtained on films fabricated at 550°C with the nozzle directed onto the substrate. In contrast, films formed with the oxygen jet directed at the target showed poor superconducting properties, with a T_c0 of approximately 50 K. The x-ray diffraction studies on these films showed much sharper Bragg peaks and higher oxygen content for films fabricated with the oxygen jet directed on the substrate compared to that of the target.