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

Hot cluster epitaxy (HCE) is a novel high-rate epitaxial growth mechanism d iscovered 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 ener gy and high sticking probability even at high substrate temperature. Actual ly, 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 mu m could not be obtained so far. In this paper, we discuss the "ch arge-up" effect of clusters and insulating substrates in a plasma environme nt as a retarding factor for film growth. Probe measurements and the biasin g deposition clarified the charge-up of clusters were charged up during dep osition. It was found that more than 60% of the clusters were negatively ch arged. By using conductive substrates of Nb doped SrTiO3, or changing Ar co mposition in Ar-O-2 plasma, we could deposit monolayer-smooth epitaxial YBa 2Cu3O7-x, films thicker than 3 mu m, with excellent properties; the full wi dth less than 0.14 degrees at half maximum of the X-ray rocking curve of th e (005) peak, and the superconducting transition temperature of 92 K. These results suggest the future role of BCE in epitaxial thick film deposition.