Improved surface morphology of NdBa 2Cu 3O 7− δ films grown by pulsed laser deposition using a large single crystal target

Abstract

Smooth surface is one of the essential factors for high- T c thin film device fabrications. To obtain smooth NdBa 2Cu 3O 7− δ (NBCO) films by pulsed laser deposition (PLD), a large NBCO single crystal was used as the target instead of sintered ceramic pellet in PLD for the first time. Although NBCO films grown at optimum conditions from either a sintered or a single crystal target possessed similar excellent superconducting properties with zero resistance temperature T c0=91–94 K and current density J c>3×10 6 A/cm 2 at 77 K, they displayed a quite different surface morphology. A great improvement of surface quality was achieved by using the single crystal target. High-resolution scanning electron microscopy images showed that the droplet density on the surface of NBCO films deposited from the single crystal target was reduced by a factor of 10 4, i.e., from 10 6–10 7/cm 2 corresponding to the sintered target to 10 2–10 3/cm 2. Atomic force microscope observation revealed that the line-scan surface roughness was <40 Å over an area of 2×2 μm 2. Our results indicate that PLD using a single crystal target is a quite easy and practical technique for the growth of smooth superconducting films for device applications.