Formation of Hollow Gallium Nitride Spheres via Silica Sphere Templates

We report the formation of hollow GaN spheres using silica sphere templates. First, silica spheres with an average diameter of ∼130 nm were synthesized. A mixture of GaCl₃, silica spheres, water, and urea in 2-propanol was prepared and heated to 100 °C for 24 h to generate silica spheres with γ-Ga₂O₃ nanoparticle shells. Decomposition of urea and its reaction with water slowly increased the solution pH to ∼8; this controlled reaction is the key to forming uniform γ-Ga₂O₃ shells with a thickness of about 13 nm. The amounts of urea and water have been varied to find the optimal conditions for the preparation of the oxide shells. Transfer of the colloidal particle solution to silicon substrates and ammonolysis at 850 °C for 6 h produced the SiO₂−GaN core−shell nanostructures. Immersion of the silicon substrates in an HF solution removed the silica cores, and hollow GaN spheres with a shell thickness of around 8 nm were formed. The morphologies and crystal structures of the oxide and nitride shells have been carefully examined. The GaN shell materials show an absorption band at 350−360 nm and a broad defect-related emission band centered at around 570 nm.