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

The basic growth mode of a thin epitaxial cuprate film (<200 Å) 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{-}\mathrm{\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{-}\mathrm{\delta }}$ films over a large area (∼0.5 cm×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.