Ammonothermal synthesis of thick gallium nitride film employing acidic mineralizers

Fabrication of wurtzite-type gallium nitride (GaN) thick films on HPVE-grown {0001} GaN substrates under moderate ammonothermal conditions is reported. Supercritical ammonia (NH3) as solvent and the mineralizer ammonium chloride (NH4Cl) is employed for temperature and pressure conditions of 400–550 °C and ≤135 MPa, respectively. Growth rates of 30 μm per day over long-term growth runs were obtained. The effect of surface morphology of the substrate on homoepitaxial nucleation of GaN films prepared from ammonoacid solutions is investigated. Two-dimensional nucleation is obtained for substrates etched by hot concentrated KOH prior film growth. In this case the interface between film and the ( \( 000\overline 1 \)) substrate does not show any signs of voids or island nucleation. Cracking pattern reveals similar mechanical-elastical properties for film and substrate.