Growth of rock-salt MgO-NiO-ZnO films: Relationship between lattice constant and composition

Abstract

Deep-ultraviolet light-emitting diodes (DUV-LEDs) have emerged as eco-friendly alternatives to mercury lamps for various applications. This study explores MgO-NiO-ZnO alloy semiconductors as potential materials for DUV-LEDs, offering advantages over conventional AlGaN-based systems. MgO-NiO-ZnO films with varying compositions were grown using mist chemical vapor deposition (mist-CVD) and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and UV-visible spectroscopy. A single-phase rock-salt structure was obtained for ZnO mole fractions of up to 0.26, whereas phase separation occurred at higher levels of ZnO content. The lattice constant-composition relationship followed Vegard's law, suggesting that MgO-NiO-ZnO films with a composition of Mgₓ(Ni₀.₆₇Zn₀.₃₃)₁₋ₓO could achieve lattice matching with MgO substrates. The band gaps of rock-salt MgO-NiO-ZnO, determined based on spectral transmittance measurements, ranged from 5.4 eV to 5.8 eV and increased with MgO content. These band gap values are sufficient for DUV-LED applications. This study provides crucial insights into MgO-NiO-ZnO alloy semiconductors, paving the way for the development of more efficient and strain-free DUV-LEDs.