Gallium nitride powders: Mechanism of ammonothermal synthesis, ball-mill assisted rare earth doping and uniform electrophoretic deposition

Based on free molecular flow analysis and powder growth experiments, we present evidence that ammonothermal synthesis of GaN powders is primarily a liquid phase process. Rare earth doped GaN nanopaticles were synthesized from as-prepared GaN using a ball-mill assisted solid state reaction. The ball-milled powders were heat treated under different conditions to facilitate dopant diffusion. Luminescence properties of the rare earth doped GaN powders in the near infrared regime were investigated using a photoluminescence (PL) apparatus. The maximum PL at 1.55 μm (C band) was obtained from Er/Tb co-doped GaN annealed in air at 923 K for 4 h. The nanosized GaN particles was then uniformly deposited on a suitably prepared glass substrate using a home built electrophoretic set. A suspension of ethanol, glycerol, Mg(NO3)2 and nanosized GaN was used in the electrophoretic bath. Use of electric fields in the range 80–100 V cm−1 and constant current density of ∼1.60 mA cm−2 gave uniform and complete coverage of GaN on the substrate.