Method of manufacturing a group III-nitride crystal comprising a nucleation step, a pyramid growth step, a lateral growth step, and a flat thick film growth step

1. A method of manufacturing a group-III nitride crystal comprising:

a seed crystal preparation step of preparing a plurality of dot-shaped group-III nitrides on a substrate as a plurality of seed crystals for growth of a group-III nitride crystal; and

a crystal growth step of bringing surfaces of the seed crystals into contact with a melt comprising an alkali metal and at least one group-III element selected from the group consisting of gallium, aluminum, and indium in an atmosphere comprising nitrogen and thereby reacting the group-III element with the nitrogen in the melt to grow the group-III nitride crystal,

wherein the crystal growth step comprises:

a nucleation step of forming a plurality of crystal nuclei from the plurality of seed crystals;

a pyramid growth step of growing a plurality of pyramid-shaped first group-III nitride crystals from the plurality of crystal nuclei;

a lateral growth step of growing second group-III nitride crystals so that gaps of the plurality of pyramid-shaped first group-III nitride crystals are filled to form a flattened surface; and

a flat thick film growth step of growing a third group-III nitride crystal having a flat surface after the lateral growth step;

wherein the nucleation step is performed at 874° C. or less, the pyramid growth step is performed at a crystal growth temperature of 877° C. or more, the lateral growth step is performed at a crystal growth temperature of 877° C. or more, and the flat thick film growth step is performed at 862° C. to 874° C.

2. The method of manufacturing a group-III nitride crystal according to claim 1 , wherein at the nucleation step, the plurality of seed crystals are immersed in the melt within 5 minutes to 10 hours.

3. The method of manufacturing a group-III nitride crystal according to claim 1 , wherein at the lateral growth step, multiple group-III nitride crystal layers are formed on inclined planes of the pyramid-shaped first group-III nitride crystals by repeatedly immersing the substrate into the melt and pulling up the substrate from the melt.

4. The method of manufacturing a group-III nitride crystal according to claim 1 , wherein the pyramid growth step is performed at the same temperature as the crystal growth temperature of the lateral growth step.

5. The method of manufacturing a group-III nitride crystal according to claim 1 , further comprising a step of separating the group-III nitride crystal and the substrate after the crystal growth step.

6. The method of manufacturing a group-III nitride crystal according to claim 1 , wherein the flat thick film growth step is performed at 870° C. to 874° C.