Congruent Melting of Gallium Nitride under High Pressure and Its Application to Single Crystal Growth

GaN (Gallium Nitride) is an important material in optoelectronic devices for blue light-emitting diodes and lasers. Large-size single crystals of GaN are strongly desired, which can be used as substrates for epitaxial growth. We made in situ X-ray diffraction experiments using a multi-anvil high-pressure apparatus at the SPring-8 to confirm its decomposition and melting behavior under high pressures and temperatures. Congruent melting of GaN occurred around 2220 °C at pressures above 6.0 GPa, and decreasing the temperature allowed the GaN melt to crystallize to the original structure. This result leads to a new synthesis method of high quality single crystals of GaN by means of slow cooling of its stoichiometric melt under high pressure. Single crystal of GaN with a diameter of 100 μm has been obtained successfully that shows a sharp X-ray rocking curve smaller than 30 seconds.