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 (P_N2) 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 (10 over(1, ̄) 0) (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 P_N2 had a broad deep emission peak at 617 nm, while the specimens grown at lower P_N2 had a shallow-level emission peak at 380 nm and a broad deep emission peak at 550 nm.