Development of bulk GaN single crystal substrate for high-power ultra-violet laser diodes

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In this research, we developed a full-fledged apparatus for the growth of a two-inch GaN single crystal substrate. The apparatus was designed based on the following points; 1.the electric furnace was set in a pressure-resistant chamber having a water cooling system for the growth at severe conditions, 2.the solution could be stirred by back and force the chamber. We succeeded in the growth of a two-inch GaN single crystal substrate with the dislocation density of 2.3 × 10^5 com^<-2> using this apparatus for the first time. In addition, the growth rate of 30 μm/h was achieved by optimizing the growth conditions while dislocation density was kept at 3 × 10^5 cm^<-2>.Impurity concentration in the crystal was measured by the secondary ion mass spectrometer (SIMS). The Na content in the crystal was at an extremely low level of 4.2 × 10^<14> cm^<-3> and oxygen was slightly detected, which is enough low concentration for avoiding giving harmful affect on device performance.Emission property of LED fabricated on GaN substrate grown by this method was improved in comparison to that fabricated on the other substrates such as sapphire and GaN grown by hydride vapor phase (HVPE) epitaxy method.These results have been published in many scientific papers as shown on the attached paper and attracted great attention. As mentioned above, this research enabled to produce large-scaled GaN substrate with high quality.