Optimization of KrF laser ablation parameters for in-situ growth of Y₁Ba₂Cu₃O_7−δ thin films

Abstract

Using a KrF pulsed excimer laser, various interrelated deposition parameters governing the quality of laser-ablated Y₁Ba₂Cu₃O_1−δ(123) thin films have been systematically studied. Modification of the 123 target with increasing laser exposure has been found to affect the plume stability, and the axis of the plume has been found to shift slowly towards the direction of the laser beam. Small laser spots exposing a relatively large diameter annular track of the rotating target have been found to give better plume stability than larger spots exposing the same diameter track. Because of better plume stability and larger plume expansion, smaller laser spots have been found to give significantly better quality 123 films as compared with large spots under optimised growth conditions.The effects of varying O₂ pressure and target-substrate distance have been found to be similar and the location of the substrates at or close to the tip of the plume has been found to be important for the realization of film stoichiometry and high quality. Results have shown that under optimised conditions of 3 J cm⁻² fluence, 200 m TorrO₂ pressure and 4.5 cm target-substrate distance, films with T_c= 90 K,ΔT 1 K and critical current density, J_c≥2×10₆ A cm at 77 K can be reproducibly realized on <100 > MgO substrates with small (3 mm × 0.8 mm) laser spots.