Photoluminescence investigation of epitaxial ZnGeN₂/GaN Quantum Wells

Current InGaN/GaN structures are unable to emit efficiently at wavelengths longer than ~525 nm due to spontaneous polarization and phase separation reducing the radiative recombination rate, creating a need to expand the design space of nitride LEDs. ZnGeN₂/GaN quantum well structures are proposed as a solution to this green gap. ZnGeN₂ is almost lattice-matched to GaN, enabling integration into GaN-based systems for an expanded emission space with much less lattice mismatch than InGaN. ZnGeN₂/GaN QWs were grown using molecular beam epitaxy (MBE) demonstrating room-temperature and low-temperature photoluminescence (PL). Possible emission sources including defect emission, band-to-band (cation disorder), and spatially indirect excitons from band offsets will be discussed based on experiment and theory. Transmission electron microscopy (TEM) images show abrupt interfaces, which is promising for future device applications. Electronic structure calculations for ZnGeN₂/GaN show band gap reduction from disorder and a type II alignment, informing our understanding of the system.