  Control of thin film stoichiometry is of primary relevance to achieve desired
functionality. Pulsed laser deposition ablating from binary-oxide targets
(sequential deposition) can be applied to precisely control the film
composition, offsetting the importance of growth conditions on the film
stoichiometry. In this work, we demonstrate that the cation stoichiometry of
SrTiO$_3$ thin films can be finely tuned by sequential deposition from SrO and
TiO$_2$ targets. Homoepitaxial SrTiO$_3$ films were deposited at different
substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a
growth window for stoichiometric SrTiO$_3$. The growth kinetics and nucleation
processes were studied by reflection high-energy electron diffraction and
atomic force microscopy, providing information about the growth mode and the
degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions,
films exhibit atomically flat surfaces, whereas off-stoichiometry is
accommodated by crystal defects, 3D islands and/or surface precipitates
depending on the substrate temperature and the excess cation. This technique
opens the way to precisely control stoichiometry and doping of oxide thin
films.
