Effect of atomic oxygen on the initial growth mode in thin epitaxial cuprate films

Abstract

The basic growth mode of a thin epitaxial cuprate film (200 A\r{}) on a given substrate depends sensitively on the balance between various thermodynamic and kinetic factors related to the high-${\mathit{T}}_{\mathit{c}}$ phase formation and the surface microstructure at the growth front of the deposited film. Under the standard optimized growth conditions for high-quality epitaxial films, the deposition of a ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ film on an atomically smooth (110) ${\mathrm{SrTiO}}_{3}$ substrate, for example, is characterized by a strong damping in the reflection high-energy electron diffraction (RHEED) oscillation suggesting a predominant island growth mode. We have demonstrated that with an atomic oxygen and the technique of RHEED-controlled growth interruption it is possible to minimize surface roughness and to fabricate unit-cell smooth ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ films over a large area (\ensuremath{\sim}0.5 cm\ifmmode\times\else\texttimes\fi{}1 cm). The results of this study suggest that two-dimensional layer growth can be induced by the combined use of atomic oxygen and growth conditions, such as low deposition rate, low oxygen partial pressure (2 mTorr), that produce low supersaturation at the growth front.