Acidic ammonothermal growth of gallium nitride
in a liner-free molybdenum alloy autoclave

This paper discusses promising materials for use as internal, non-load bearing components as well as molybdenum-based alloys for autoclave structural components for an ammonothermal autoclave. An autoclave was constructed from the commercial titanium–zirconium–molybdenum (TZM) alloy and was found to be chemically inert and mechanically stable under acidic ammonothermal conditions. Preliminary seeded growth of GaN was demonstrated with negligible incorporation of transition metals (including molybdenum) into the grown material (<10¹⁷ cm⁻³). Molybdenum and TZM were exposed to a basic ammonothermal environment, leading to slight degradation through formation of molybdenum nitride powders on their surface at elevated temperatures (T > 560 °C). The possibility of a ‘universal’, inexpensive, liner-free ammonothermal autoclave capable of exposure to basic and acidic chemistry is demonstrated. (Read full text)