# Blue-Green Emission from Epitaxial Yet Cation-Disordered ZnGeN$_{2-x}$O$_x$

## TL;DR

This study demonstrates the synthesis of cation-disordered ZnGeN$_{2-x}$O$_{x}$ thin films with tunable optoelectronic properties, showing potential as low-cost blue-green light emitters despite structural disorder.

## Contribution

It provides a novel synthesis approach for cation-disordered ZnGeN$_{2-x}$O$_{x}$ with optoelectronic properties suitable for green emission applications.

## Key findings

- X-ray diffraction confirms wurtzite structure with 6-fold symmetry.
- Photoluminescence peaks between 2.4 and 2.8 eV indicating optical activity.
- Epitaxial films exhibit semi-coherent interfaces with dislocations relieving strain.

## Abstract

ZnGeN$_2$ offers a low-cost alternative to InGaN with the potential for bandgap 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 ZnGeN$_{2-x}$O$_{x}$ thin film library grown by combinatorial co-sputtering on c-Al$_2$O$_3$. Samples exhibit X-ray diffraction patterns and X-ray pole figures characteristic of a wurtzite (cation-disordered) structure with the expected 6-fold in-plane symmetry. Transmission electron microscopy reveals a semi-coherent interface with periodic dislocations that relieve strain from the large lattice mismatch, and 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 ZnGeN$_{2-x}$O$_{x}$, indicating a path toward application as a blue-green emitter.