Towards efficient green emitters: Heteroepitaxial ZnGeN₂ on GaN by molecular beam epitaxy

GaN-based LEDs have revolutionized the lighting industry, yet phosphor converters are still required to achieve green and amber wavelengths in a white light emitter. The ‘green gap’ refers to this lack of efficient emitters from 510 nm – 610 nm. InGaN active layers theoretically can reach this range, however the increased In-content results in complications including phase separation and increased spontaneous polarization mismatch which leads to decreased radiative recombination efficiency.
II-IV-N₂ materials are an optically relevant class of materials with direct gaps across the visible spectrum. ZnGeN₂ is nearly lattice matched to GaN, providing a direct route to device integration within a mature system, and can potentially enable green and amber emission at much lower lattice mismatch than InGaN.
The heteroepitaxial growth of ZnGeN₂ on GaN by molecular beam epitaxy will be discussed, highlighting the impact of Zn desorption and interfacial surface energy on nucleation rate. Insights into growth regimes and limitations will be given, highlighting practical considerations for the characterization of potentially cation-disordered materials. Heterostructure growth represents a major step toward enabling hybrid III-N/II-IV-N₂ optical devices.