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

在这项研究中，我们开发了一台成熟的设备来生长两英寸的GaN单晶衬底。该装置是根据以下几点设计的：1.电炉设置在具有水冷却系统的耐压室中，以便在严酷的条件下生长；2.溶液可以通过背部搅拌并强制室内生长。利用该装置首次成功地生长了2英寸GaN单晶衬底，其位错密度为2.3×10~(-5)cm~(-2)。此外，通过优化生长条件，在保持位错密度为3×105 cm~(-2)的条件下，获得了30μm/h的生长速率。晶体中Na的含量非常低，只有4.2×10^-lt；14-gt；cm-3-gt；-3-gt；有少量的氧，这是一个足够低的浓度，可以避免对器件性能造成有害的影响。与用氢化物气相外延方法生长的蓝宝石和GaN等其他衬底相比，用这种方法生长的LED的发光性能得到了改善。这些结果已经发表在许多科学论文上，如所附的论文所示，引起了极大的关注。如上所述，这项研究使得能够生产出高质量的大规模GaN衬底。

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.