  Making a systematic effort, we have developed a single-crystalline ZnSnN2 on
ZnO (0001) by reactive magnetron co-sputtering. Epitaxial growth was achieved
at 350 C by co-sputtering from metal targets in nitrogen atmosphere, and
confirmed by transmission electron microscopy (TEM) measurements. TEM verified
that the layers are single-crystalline of hexagonal phase, exhibiting epitaxial
relationship with the substrate. The screw-type threading dislocations
originating from the interface were identified as dominant extended defects.
More specifically, we report a pioneering measurement of the dislocation
density in this material. Even though, there is no literature data for direct
comparison, such values are typical of heteroepitaxial growth of III-nitride
layers without applying defect density reduction strategies. The films
demonstrated a record electron mobility. The optical bandgaps of 1.86 eV and
1.72 eV were determined for the stoichiometric and Zn-rich samples,
respectively. As such, we conclude that ZnSnN2 is an earth-abundant,
environmentally-friendly semiconductor and is a promising candidate for cost
efficient components in electronics and photonics.

Materials Science