Combinatorial Investigation of Structural and Optical Properties of Cation-Disordered ZnGeN₂

In this work, we present a combinatorial study of sputtered ZnGeN₂ thin films with cross-cutting applications in fundamental materials science and novel device development. The II-IV-N₂ materials offer the possibility of 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 experimental studies to date report inconsistent optical properties. Additionally, minimal work has explored variation with cation composition, which has been shown to impact properties of other II-IV-N₂ materials. Here, we present a study of combinatorial ZnGeN₂ grown by RF co-sputtering. X-ray diffraction reveals phase-pure films in the expected cation-disordered wurtzite structure for cation compositions from 30% to 60% Zn/(Zn+Ge) and synthesis temperatures from 200°C to 600°C. Changes in crystallinity are explored as a function of cation composition, synthesis temperature, and in-situ and ex-situ annealing. Finally, spectroscopic ellipsometry is performed to investigate optical properties with changing synthesis conditions. This study re-affirms the potential for tunability of thin film ZnGeN₂ as a direct- and wide- bandgap optoelectronic material.