Growth of GaN crystals from chlorine-free gas phase

The aim of this research is the development of an efficient chlorine-free growth process for GaN bulk crystals. Ga evaporated from a heated melt is transported to the substrate where it reacts with reactive nitrogen generated from the decomposition of ammonia to form gallium nitride. Numerical simulation was used to optimise the set-up geometry and growth regime. It was observed that growth rate and layer quality are influenced by typical growth parameters such as temperature, total pressure and ammonia flow, as well as by source composition, crucible material and flow conditions in the growth area. Initially, mm-sized crystallites were deposited on the seed holder with growth rates well above 10 μm/h, which proved the potential of the method. Recently, the work was focused on the deposition on various single crystalline substrates. Epitaxial layers up to a bulk-like thickness of 280 μm were achieved on GaN-sapphire templates.