Optimizing Metal‐Organic Chemical Vapor Deposition for Ultrawide Bandgap MgSiN ₂ Thin‐Films

Orthorhombic II–IV nitride semiconductors offer an expanded and more tunable material set with unique properties while maintaining close compatibility with the wurtzite crystal structure of the III‐nitrides. In particular, MgSiN ₂ , a II–IV nitride closely lattice matched to GaN and AlN, has a bandgap suitable for photonic applications in the UV‐C wavelength region. MgSiN ₂ is also a promising candidate to exhibit ferroelectricity, which has only been observed in very few nitride materials. This study builds on previous work on the metal‐organic chemical vapor deposition of MgSiN ₂ thin‐films grown on GaN‐on‐sapphire and c‐plane sapphire substrates by exploring higher growth temperature windows, resulting in higher crystalline quality and improved interfaces. Correlations between the growth conditions (Mg:Si precursor molar flow rate ratio, reactor pressure, and growth temperatures from 900 to 960 °C) and the resultant film quality are investigated for films grown on GaN‐on‐sapphire. High‐resolution transmission electron microscopy reveals high‐quality orthorhombic single‐crystal MgSiN ₂ , confirming successful epitaxial growth on GaN. Optical transmittance measurements indicate the direct bandgap of 6.34–6.36 eV and the indirect bandgap of 5.77–5.81 eV, affirming the realization of an ultrawide bandgap II–IV nitride semiconductor that is structurally compatible with existing III‐nitride device platforms.