Self-regulating MBE growth of stoichiometric BaSnO$_{3}$ films \textit{via} reactive radical mechanism*

Growth of thin films comprising of element with low oxidation potential such as Sn often requires reactive oxidants such as ozone or high-pressure oxygen plasma. By utilizing the chemistry of highly reactive radical of Sn, we will present on the growth of phase-pure, epitaxial BaSnO$_{3}$ films using a hybrid molecular beam epitaxy (MBE) approach with scalable growth rates. The notable finding was that Sn radicals are very reactive to yield phase-pure BaSnO$_{3}$ films even in molecular oxygen [1]. In this approach, we use hexamethylditin (HMDT) as a tin source, a solid effusion cell for Ba and either molecular oxygen or an rf oxygen plasma source. Phase-pure BaSnO$_{3}$ films were grown at 900 $^{0}$C, and oxygen pressure of 5x10$^{-6}$ Torr as a function Sn:Ba ratio. \textit{In-situ} time-dependent RHEED intensity oscillations were observed establishing a layer-by-layer growth mode and a critical thickness of $\approx $1 nm for strain relaxation [1]. Rutherford backscattering spectrometry and lattice constant determined using high-resolution X-ray diffraction was used to optimize cation stoichiometry. ``MBE growth window'' was identified where films show bulk-like lattice parameter (4.116 {\AA}) over a wide-range of cation flux ratios. A correlation between RHEED patterns, stoichiometry, and surface morphology was established. [1] A. Prakash \textit{et al.}, J. Vac. Sci. {\&} Technol. A \textbf{33}, 060608 (2015).