Synthesis of nanocrystalline aluminum–gallium nitride (Al_xGa_1−xN; x = 0.1 to 0.5) with oxide precursors via ammonolysis

Oxygen-containing precursor systems for the synthesis of mixed aluminum–gallium nitride (Al_xGa_1−xN with x = 0.1 to 0.5) through ammonolysis (heat treatment under ammonia) were evaluated. Three different precursor systems were studied: (i) aluminum isopropoxide (aluminum sec-butoxide)/gallium isopropoxide hydrolyzed with excess water and cross-linked with 1,6-hexanediol, (ii) aluminum–gallium hydroxide coprecipitated from aluminum–gallium nitrate solution, and (iii) spray-dried aluminum–gallium nitrate solutions. The specimens were heat-treated between 700 °C and 1100 °C and were characterized mainly by x-ray diffraction, nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). NMR was used to follow the conversion of oxygen to nitrogen bonds. TEM in combination with energy-dispersive x-ray spectroscopy was used to determine the solid-solution composition for separated particles. It is possible to synthesize a mixed hexagonal (Al,Ga)N with crystallite sizes in the range of ∼10 nm from all three precursor systems, but all products contained larger GaN crystals ranging from 20 nm (alkoxide-derived) to 200 nm (hydroxide-derived) and a fraction of untransformed Al–O bonds; e.g., (amorphous or γ-phase) Al₂O₃.