This method makes it possible to grow crystals with fewer defects than previously. Currently, gallium nitride substrates are produced by thick-film crystal growth using a vapor growth method called the VPE method. However, with this method a defect involving dislocation at a density of about 104 to 106cm-2 (10,000 to 1,000,000 defects per square centimeter) is generated, and this defect greatly deteriorates device performance. On the other hand, the flux method, a liquid-phase growth method, makes possible higher-quality crystals having dislocation density of about 103cm-2. This makes it possible to dramatically increase device performance. Also, the flux method enables growth of platelet crystals having a c-plane (polar plane) and prismatic crystals having an m-plane (non-polar plane) as a facet, which are important for device production, by controlling crystal growth conditions such as temperature and pressure (Figure 3).