Ammonothermal Growth of GaN Under Ammono-Basic Conditions

Abstract

We are presenting some physical and chemical basics of the ammonothermal method of bulk gallium nitride synthesis in ammonobasic regime. Excellent structural parameters and a wide spectrum of electrical properties of truly bulk GaN crystals are revealed. In the considered crystals, a low dislocation density (5 ×10³ cm ^{− 2}) is attained. At the same time, the crystal lattice is extremely flat, and the rocking curve is very narrow (FWHM = 16 arcsec). Regardless of the crystal size, the radius of lattice curvature is higher than 100 m, whereas in the best crystals it is higher than 1,000 m. Both polar and nonpolar ammonothermal GaN substrates with perfect crystalline properties enable growth of excellent quality, strain-free homoepitaxial layers. The luminescence is dominated by an intensive, perfectly-resolved excitonic structure which is uniform in the whole range of sample surface. In high excitation conditions, a biexciton emission is observed. High PL homogeneity corresponds well with structural and microscopic measurements performed on these layers. The authors are convinced, that due to perfect scalability of the ammonothermal method, large-diameter (above 2 in.) bulk GaN substrates can be employed in mass production. This will make a breakthrough in the manufacturing of high-power GaN-based devices.