Growth of GaN crystals by Na flux method under 7 MPa nitrogen pressure

GaN pyramid shaped crystals with millimeter size have been grown by temperature gradient-applied Na flux method under 7 MPa nitrogen pressure, the yields up to 70% or more. The morphologies of GaN crystals were observed with an optical microscope and a scanning electron microscope. The quality of GaN crystal was checked by X-ray powder diffraction, X-ray rocking curve and photoluminescence (PL) spectra. The full-width at half-maximum (FWHM) of X-ray rocking curves measured for {101̄1} reflection of the crystals was 4.4 arcsec. From the room temperature photoluminescence spectrum (PL) of an as-grown GaN single crystal, a strong unique and narrow peak centered at 365 nm can be observed, and its FWHM was only 13.5 nm. Which show that GaN crystals obtained by this method possess good crystalline quality.