Heteroepitaxial ZnGeN2 on AlN: Growth, Structure, and Optical Properties

ZnGeN2 is a potential green-to-amber emitter which can be integrated into existing GaN LED heterostructures due to structural similarity. However, for accurate material characterization, ZnGeN2 must be grown without GaN due to their similar optical and structural properties. This is exemplified by ZnGeN2/GaN heterostructures with luminescence signatures that overlap a well-known Zn-doped GaN blue luminescence band. In this work we present the molecular beam epitaxy growth of ZnGeN2 on lattice mismatched AlN templates with regrown AlN buffer layers enabling GaN-free structural and optical characterization. Fully relaxed ZnGeN2 on AlN shows cation-disordered lattice parameters a = 3.1962 Å ± 0.0032 Å and c = 5.2162 Å ± 0.0015 Å (c/a ratio = 1.632) determined from multiple reflections and a least-squares regression. Reflection high-energy electron diffraction, X-ray diffraction, and atomic force microscopy characterization reveal an optimal growth temperature for ZnGeN2 on AlN of 450 °C. Photoluminescence shows broad recombination centered around 2.96 eV, clearly attributed to ZnGeN2, which is distinct from the 2.88 eV Zn-doped GaN blue luminescence band. This work offers insight into the properties of ZnGeN2, enabling new characterization and new heteroepitaxial devices based on AlN.