Growth of GaN Crystals by the Na Flux Method Under a Temperature Gradient

Abstract

The effects of temperature gradients on the growth of GaN crystals by the Na flux method were investigated. Yields of GaN pyramid crystals of up to 70% were obtained by use of temperature gradients of 40–70°C/cm and 7 MPa nitrogen pressure. The crystals were obtained by spontaneous nucleation growth. Introducing a moderately large temperature gradient can suppress formation of a hard polycrystalline surface layer at the gas–liquid interface and aid transfer of heat and solute, resulting in controllable GaN crystal growth and better yield of GaN crystals. The maximum size of GaN crystals with hexagonal pyramidal faces was approximately 3 mm. The full-width at half-maximum of the rocking curve measured for the $\left( {10\bar 11} \right)$x-ray diffraction peak was only 36 arcsec. A emission peak at approximately 365 nm was observed at room temperature by photoluminescence spectroscopy. Characterization suggested the GaN crystals were of good crystalline quality.