Examination of Effects of H_2 Concentration in Reactant Gas on GaN Growth by Gallium Hydride Vapor Phase Epitaxy

摘要

The dependence of H_2 concentration in a reactant gas on the rate of GaN single crystal growth by gallium hydride vapor phase epitaxy (GaH-VPE) method was investigated. In the GaH-VPE, gallium hydride (GaH_x), which was synthesized by introducing H_2 gas into Ga melt, reacts with NH_3 to form GaN single crystals. Growth rate increased with a H_2 concentration less than 20 mol % and reached a maximum at H_2 concentration of 20 mol %. However, too much H_2 gas decreased the growth rate. The observation of the surface morphology of grown films by scanning electron microscopy (SEM) clarified that H_2 gas, which did not contribute to the reaction with Ga for GaH_x formation, promoted the decomposition of GaN at a high H_2 concentration. This study gave us the knowledge that the growth rate of GaN crystals greatly depends on the reaction efficiency between Ga and H_2. In addition, GaN film with a smooth surface was grown at a high NH_3/GaH_x ratio.