Deposition of high-critical-temperature superconductor YBa2Cu3O7-x epitaxial thick film by hot cluster epitaxy

Abstract

Hot cluster epitaxy (HCE) is a novel high-rate epitaxial growth mechanism discovered in the study of the plasma flash evaporation method. In HCE, the main deposition species are thermally activated, nanometer-scale clusters (hot clusters), which have unique characteristics such as high internal energy and high sticking probability even at high substrate temperature. Actually, with HCE, deposition of YBa2Cu3O7-x epitaxial films at a growth rate of 16 nm/s on the SrTiO3 substrate has been achieved. However, films thicker than 2 μm could not be obtained so far. In this paper, we discuss the "charge-up" effect of clusters and insulating substrates in a plasma environment as a retarding factor for film growth. Probe measurements and the biasing deposition clarified the charge-up of clusters were charged up during deposition. It was found that more than 60% of the clusters were negatively charged. By using conductive substrates of Nb doped SrTiO3, or changing Ar composition in Ar-O2 plasma, we could deposit monolayer-smooth epitaxial YBa2Cu3O7-x films thicker than 3 μm, with excellent properties; the full width less than 0.14° at half maximum of the X-ray rocking curve of the (005) peak, and the superconducting transition temperature of 92 K. These results suggest the future role of HCE in epitaxial thick film deposition.