Oxygen post-annealing effects on critical current properties of PLD-ErBa₂Cu₃O_y films grown at several substrate temperatures

We report the effects of oxygen post-annealing on critical current properties and normal state resistivities in ErBa₂Cu ₃O_y/SrTiO₃(Er123/STO) thin films fabricated in the substrate temperature range from 720 °C to 780 °C by pulsed laser deposition (PLD). Interestingly, for films fabricated below 760 °C, the critical current density (J_c) increased by oxygen post-annealing process from 0.3-0.6 × 10⁶ A cm^-2 to the order of 10⁶ A cm^-2 for the as-deposited films despite critical temperatures (T_c) of ∼90 K for both annealed and as-deposited films. In the 780 °C-deposited film, J_c was not obviously enhanced. X-ray diffraction and measurement of normal state resistivities revealed that the PLD-Er123/STO films showed high-quality crystallographic and electrical properties in films deposited below 760 °C. In high temperature resistivity measurements, the resistivity reduced with annealing time and showed a systematic change with changing oxygen partial pressure. These results strongly suggest that oxygen post-annealing is indispensable for improving J_c in 123 films fabricated through a non-equilibrium process such as the PLD method even though the as-deposited films show a T_c value of ∼90 K.