Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth

Utsumi, Wataru; Saito, Hiroyuki; Kaneko, Hiroshi*; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

Synthesis of large single crystal GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue light-emitting diodes and lasers. Although high quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melt of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred around 2220C, and decreasing the temperature allowed the GaN melt to reversibly back-transform into the original crystal structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.