Growth of colorless transparent GaN single crystals on prismatic GaN seeds using a Ga melt and Na vapor

Growth of GaN on seeds of GaN prismatic single crystals was carried out at 900 °C and N₂ pressure (PN₂) of 0.8-7.0 MPa for 72 h by the Na flux method using premixed Na-Ga melts or Ga melt and Na vapor. Black GaN crystals, having some pits and striations on the facets, grew on the seeds when the premixed Na-Ga melts were used. A full-width at half maximum (FWHM) of the X-ray rocking curve measured for the (m plane) of the grown crystals was over 360 arcsec. Colorless and transparent GaN crystals with smooth facets were grown on the m plane of the seed crystals by using a Ga melt and Na vapor. The FWHM measured for the m plane of the colorless crystals was 112-204 arcsec. Cathodoluminescence (CL) spectra from the m plane of the crystals were measured at room temperature. Besides a near-band-edge (NBE) emission at 361-363 nm, the specimens grown with Ga melt and Na vapor at higher PN₂ had a broad deep emission peak at 617 nm, while the specimens grown at lower PN₂ had a shallow-level emission peak at 380 nm and a broad deep emission peak at 550 nm.