Blue-green emission from epitaxial yet cation-disordered ZnGeN2−xOx

${\mathrm{ZnGeN}}_{2}$ offers a low-cost alternative to InGaN with the potential for band-gap tuning to span the green gap using cation site ordering. The addition of oxygen on the anion site creates an additional degree of electronic tunability. Here, we investigate the structure and optoelectronic properties of an epitaxial ${\mathrm{ZnGeN}}_{2\ensuremath{-}x}{\mathrm{O}}_{x}$ thin film library grown by combinatorial co-sputtering on c-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$. Samples exhibit x-ray diffraction patterns and x-ray pole figures characteristic of a wurtzite (cation-disordered) structure with the expected sixfold in-plane symmetry. Transmission electron microscopy reveals a semicoherent interface with periodic dislocations that relieve strain from the large lattice mismatch and also confirms the in-plane and out-of-plane crystallographic orientation. Room-temperature photoluminescence exhibits peaks between 2.4 and 2.8 eV which are consistent with a sharp absorption onset observed by UV-vis spectroscopy. These results demonstrate low-cost synthesis of optically active yet cation disordered ${\mathrm{ZnGeN}}_{2\ensuremath{-}x}{\mathrm{O}}_{x}$, indicating a path toward application as a blue-green emitter.