(Invited) Evaluation of 2" Power-Grade GaN Substrates Produced By the Near Equilibrium Ammonothermal (NEAT) Method

Abstract

This paper provides evaluation of 2" GaN substrates produced by the near equilibrium ammonothermal (NEAT) method. Ammonothermal growth is a proven method of producing low-dislocation GaN crystals with practical productivity. [1, 2] By choosing a near-equilibrium growth condition, consistent growth with maintained crystal quality has been achieved. [3] Several tens of bulk GaN crystals were grown simultaneously, yielding many 2" GaN substrates in one growth batch. Figure 1 is an example of bulk GaN crystals after shaping and Figure 2 is an example of 2" GaN wafer.We have developed an X-ray mapping technique which presents the distribution of full width half maximums (FWHMs) of rocking curves from 002 and 201 diffractions over a 2" wafer. The X-ray mapping revealed superior microstructure quality of NEAT GaN substrates. NEAT GaN substrates typically show an average full width half maximum (FWHM) of the 002 X-ray rocking curve of 30 arcsec or better, as shown in Figure 3.The X-ray mapping data were compared with other characterization techniques, including X-ray topography. X-ray topography confirmed that a dislocation density of typical NEAT GaN substrate was about 2 x 105 cm-2. Wide area X-ray topography also revealed flatter lattice of a NEAT GaN substrate compared with a GaN substrate fabricated by hydride vapor phase epitaxy (HVPE).Additionally, recent progress in oxygen reduction yielded NEAT GaN substrates with reduced residual donors, coloration and optical absorption. The oxygen concentration was about 2 x 1018 cm-2. An absorption coefficient of 1.3 cm-1 was obtained at 450 nm.The usability of NEAT GaN substrates was also confirmed through device fabrication. Multiple collaborators successfully fabricated high-power diodes with breakdown voltage over 1000V.