Combinatorial Insights into the Structure and Properties of Cation-Disordered ZnGeN₂

In this work, we present a combinatorial investigation of sputtered ZnGeN₂ thin films with cross-cutting applications in fundamental materials science and development of optical devices. The II-IV-N₂ materials offer potentially groundbreaking optoelectronic properties through greater chemical and structural tunability than the III-Ns. ZnGeN₂ is lattice-matched to GaN and is predicted to exhibit a direct bandgap with strong absorption, but inconsistent optical properties have been reported to date. Additionally, minimal work has explored variation with cation composition. Here, we present a study of combinatorial ZnGeN₂ grown by RF co-sputtering. X-ray diffraction reveals films in the cation-disordered wurtzite structure for a significant window of cation compositions and synthesis temperatures. Pawley refinements reveal a linear shift in unit cell volume with off-stoichiometry, indicating alloy-like behavior consistent with a cation antisite defect model. Finally, spectroscopic ellipsometry is performed to investigate optical properties. This study re-affirms the potential for tunability of ZnGeN₂ as a direct- and wide- bandgap optoelectronic material.