Influence of Na : Ga ratios under the flux-excess aid on GaN crystal growth using the Na-flux LPE method

Abstract

GaN crystals were grown on MOCVD-GaN films using the Na-flux liquid-phase epitaxial method with a new flux-excess aid technology. The impact of Na : Ga ratio variation on crystal growth under stable melt conditions was investigated. As the Ga content increased, the surface morphology of GaN crystals tended to become flatter. At Na : Ga ratios of 80 : 20, 70 : 30, and 60 : 40, the as-grown GaN crystal thicknesses were 810 μm, 1500 μm, and 530 μm, respectively, with the XRC-FWHM of the (0002) plane of 4100 arcsec, 344 arcsec, and 349 arcsec, respectively. Simulations calculated the distribution of the N ion concentration on the seed crystal surface at the onset of growth under different Ga contents, showing a pattern of lower concentrations in the central region and higher at the edges, with the central region being similar but the edge region decreasing with the Ga content rising. A higher concentration of nitrogen ions can degrade the quality of the crystal, while a lower concentration can reduce the epitaxial thickness. Therefore, with mitigating volatilization of Na, the starting Na : Ga ratio conducive to the growth of high-quality crystals is 70 : 30.