GaN Substrate development through the near equilibrium ammonothermal (NEAT) method and its application to higher performance GaN-based devices

摘要

This paper reviews recent development of two-inch gallium nitride (GaN) substrates fabricated by the nearequilibrium ammonothermal (NEAT) method. The NEAT method utilizes a low driving force to achieve consistentcrystal growth over a long period of time (> 90 days) while maintaining high quality microstructure. Throughrefinement of growth conditions for the NEAT method and proper preparation of seed crystals we have achieved 2"GaN substrates with excellent microstructure. Currently, 2" GaN wafers sliced from bulk GaN crystals typically havea full width half maximum (FWHM) of the 002 X-ray rocking curve of 50 arcsec or less, a dislocation density ofmid-10~5 cm~(-2) or less, and an electron density of about 2 × 10~(19) cm~(-3). The high electron density is attributed to anoxygen impurity in the crystal. Due to high oxygen concentration, GaN crystal grown in the ammonothermal methodtends to show a brownish color. Through process refinement, we successfully reduced oxygen concentration to 7 ×10~(18) cm~(-3), which resulted in optical absorption coefficient of 5.6 cm-1 at 450 nm. This progress ensures feasibility ofthe NEAT method for producing GaN wafers usable for various optoelectronic devices, power transistors andhigh-frequency transistors.