  We demonstrate the making of BaZrS3 thin films by molecular beam epitaxy
(MBE). BaZrS3 forms in the orthorhombic distorted-perovskite structure with
corner-sharing ZrS6 octahedra. The single-step MBE process results in films
smooth on the atomic scale, with near-perfect BaZrS3 stoichiometry and an
atomically-sharp interface with the LaAlO3 substrate. The films grow
epitaxially via two, competing growth modes: buffered epitaxy, with a
self-assembled interface layer that relieves the epitaxial strain, and direct
epitaxy, with rotated-cube-on-cube growth that accommodates the large lattice
constant mismatch between the oxide and the sulfide perovskites. This work sets
the stage for developing chalcogenide perovskites as a family of semiconductor
alloys with properties that can be tuned with strain and composition in
high-quality epitaxial thin films, as has been long-established for other
systems including Si-Ge, III-Vs, and II-Vs. The methods demonstrated here also
represent a revival of gas-source chalcogenide MBE.
