Synthesis of nitrogen-doped crystalline Ga₂O₃ thin films via trimethylgallium doped NH₃/H₂/N₂/O₂ premixed stagnation flames

This study presents a novel and cost-effective technique for fabricating nitrogen-doped crystalline α-Ga₂O₃ and β-Ga₂O₃ thin films under atmospheric pressure conditions through flame synthesis for the first time. We employ metal–organic ammonia (NH₃)-assisted flame synthesis (MO-NAFS) in a quasi-one-dimensional trimethylgallium (TMG) doped NH₃/H₂/N₂/O₂ flat flame to achieve a one-step deposition of Ga₂O₃ onto c-plane α-Al₂O₃ substrates. We found that hydrogen (H₂) addition directly impacts the crystallinity of the Ga₂O₃ thin film. When only NH₃ is employed as the fuel, a thin-film single-crystal nitrogen-doped β-Ga₂O₃ was observed. Blending the NH₃ with 5 % of H₂ yields a single-crystal nitrogen-doped α-Ga₂O₃, while a further increase of H₂ fraction up to 10 % results in a mixture of both α-Ga₂O₃ and β-Ga₂O₃ crystals. Remarkably, the nitrogen doping through MO-NAFS was found to persistently result in an N/O atomic ratio as high as 1.12, as determined by the XPS analysis. This approach paves the way to a simple and scalable means for producing crystalline nitrogen-doped Ga₂O₃ thin films with potential control of crystal phase composition through parameter adjustments.