Fabrication of GaN single crystals at 700°C using Na-Li-Ca mixed flux system

Abstract

GaN single crystals were grown in Na-Li-Ca flux system of which Li-Ca gradually replaces Na. X-ray powder diffraction analysis confirmed that the structure of GaN samples was wurtzite. As concentration of Li-Ca in flux increased, the shape of GaN crystals was changed from pyramidal, prism to platelets in sequence, and the color of them became transparent gradually. Among of them, the transparent prism crystals were grown first at 700°C when the concentration of Li-Ca was 31.6 mol% and 48.9 mol% in flux solution, respectively. Raman spectra implied that these crystals were stress-free and the transparent crystal grown in the high concentration of Li-Ca solution had high structural quality or low impurity concentrations.