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In a previous study, we successfully obtained a large-diameter, low-dislocation-density GaN wafer using the flux-film-coated and the multi-point-seed technique (FFC-MPST). As a production cost-cutting strategy, we are aiming to reuse a part of grown GaN crystals and produce thicker films by the Na-flux regrowth. Recently, however, it was found that threading dislocations (TDs) were generated at the growth interface in homoepitaxial growth of GaN crystals by the Na-flux method. In this study, we found that rapid growth in the regrowth contributes to the formation of inclusions causing the generation of TDs at the regrowth interface. Hence, we succeeded in suppressing the generation of TDs by a low growth rate, realized by a low-pressure condition at an initial growth stage. These findings are valuable for productivity enhancement of high-quality GaN wafers and help the widespread of GaN-based devices.

The electrical resistance of Ga-Na melt used for gallium nitride crystal growth on a Na flux was investigated with the four-point probe method. Electrical resistance of melt was measured isothermal at 870 °C as the function of time. Pressure decay measurement and crystal growth evaluation were performed and show that the electrical resistance of melt and the number of dissolved nitrogen were strongly correlated. Time-dependency of nitrogen concentration in melt was revealed and verified from the increasing growth rate. The strong correlation between measurement and crystal growth shows the high potential use of electrical resistance measurements as the monitoring method.