We demonstrate epitaxial thin film growth of the chalcogenide perovskite
semiconducting alloy system BaZrS(3βy)βSeyβ using gas-source molecular
beam epitaxy (MBE). BaZrS3β is stable in the perovskite structure in bulk
form, but the pure selenide BaZrSe3β is not. Here stabilize the full range of
compositions y = 0 ... 3 in the perovskite structure, up to and including
BaZrSe3β, by growing on BaZrS3β buffer layers. The alloy grows by
pseudomorphic heteroepitaxy on the sulfide buffer, without interruption in the
reflection high energy electron diffraction (RHEED) pattern. The resulting
films are environmentally stable and the direct band gap (Egβ) varies
strongly with Se content, as predicted by theory, covering the range Egβ =
1.9 ... 1.4 eV for y = 0 ... 3. This creates possibilities for visible and
near-infrared (VIS-NIR) optoelectronics, solid state lighting, and solar cells
using chalcogenide perovskites