Process for volume production of GaN substrates (Subtopic A: Electronic Materials)

"The objective of proposed research is to develop a commercially viable process for ammonothermal growth of gallium nitride (GaN) crystals suitable for fabrication of GaN wafers. The ammonothermal crystal growth method is modeled after the very successfulprocess of synthesizing alpha-quartz in supercritical water. In this process, a mineralizer attacks bulk nutrient to generate anions that are soluble in supercritical fluid. These small molecules migrate rapidly through the low-density fluid to appropriateseed crystals in a lower temperature zone. This creates supersaturation with resultant deposition and crystal growth. Laboratory-scale studies of GaN have demonstrated dissolution and transport in supercritical ammonia. In this Phase I STTR project, wepropose an innovative approach to develop the process for growth of GaN single crystals by the ammonothermal route to a point where it will be interesting for commercial growth of GaN. The proposed ammonothermal growth process for GaN single crystals ismodeled after the commercially highly successful synthesis of alpha-quartz in supercritical water, a process that yields an annual production volume of one thousand tons of high-quality quartz. Optimization of ammonothermal growth of GaN thus promises tolead to a commercially interesting process route for the cost-effective production of high-quality, large-area GaN single crystals. Single crystalline GaN wafers are critically needed as lattice-matched substrates for III-nitride epitaxy, in order togreatly reduce the dislocation density in overgrown, active layers. Since electronic and optoelectronic, nitride-based devices have already been grown using a variety of deposition techniques on non-lattice matched substrates, GaN substrates can beanticipated to be introduced into the marketplace without any further delay."