Tomoyuki Hattori, Norio Yamaguchi, Toshio Majima,Kazuo Terashima and Toyonobu Yoshida
Department of Metallurgy and Materials Science, Graduate School and Faculty of Engineering, The University of Tokyo, Tokyo 113-8656
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.
(Received September 9, 1998; In Final Form December 8, 1998)
plasma flash evaporation method, nanometer-scale cluster, hot cluster epitaxy, yttrium-based superconductor, charged cluster, epitaxial thick film, high deposition rate
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