Method for producing group III nitride crystal and seed substrate

1. A method for producing a group III nitride crystal, the method comprising:

seed crystal preparation including disposing a plurality of crystals of a group III nitride as a plurality of seed crystals on a substrate; and

crystal growth including growing a group III nitride crystal on each of the seed crystals by contacting a surface of each of the seed crystals with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen;

wherein in the seed crystal preparation, the plurality of seed crystals are disposed only inside a substantial regular hexagonal region provided on the substrate;

wherein the substantial regular hexagonal region is filled with the seed crystals in a form of dots with a diameter of 10 to 1,000 μm and a pitch of dots of 1.5 to 10 times the diameter;

wherein the crystal growth comprises

first crystal growth including growing a group III nitride crystal on each seed crystal into a pyramid to obtain a first group III nitride crystal formed of adjacent pyramidal group III nitride crystals partially coupled to each other, and

second crystal growth including growing second group III nitride crystal with a flat surface on the first group III nitride crystal;

wherein a distance between an outer periphery of the substrate and a center of a seed crystal the nearest to the outer periphery of the substrate among the seed crystals to be disposed in the seed crystal preparation is larger than a value obtained by dividing a maximum value of film thicknesses of the pyramidal group III nitride crystals to be grown in the first crystal growth by the square root of 3.

2. The method for producing a group III nitride crystal according to claim 1 , wherein, in the crystal growth, each side of an outer periphery of the substantial regular hexagonal region is matched up with a specific crystal plane of the group III nitride crystal.

3. The method for producing a group III nitride crystal according to claim 2 , wherein the specific crystal plane is a (1-100) plane.

4. The method for producing a group III nitride crystal according to claim 1 , wherein, among the seed crystals to be disposed in the seed crystal preparation, a seed crystal positioned the nearest to an outer periphery of the substantial regular hexagonal region has the same shape as seed crystals positioned in a center side of the substantial regular hexagonal region.

5. The method for producing a group III nitride crystal according to claim 1 , further comprising separation including separating the group III nitride crystals from the substrate in the vicinity of the seed crystals after the crystal growth.

6. A seed substrate, comprising:

a substrate; and

a plurality of seed crystals including a plurality of crystals of a group III nitride, the crystals disposed only inside a substantial regular hexagonal region provided on the substrates;

wherein the substantial regular hexagonal region is filled with the seed crystals in a form of dots with a diameter of 10 to 1,000 μm and a pitch of dots of 1.5 to 10 times the diameter.

7. The seed substrate according to claim 6 , wherein

the seed substrate is used as a growth substrate for a group III nitride crystal, and

each side of an outer periphery of the substantial regular hexagonal region is matched up with a specific crystal plane of the group III nitride crystal.

8. The seed substrate according to claim 7 , wherein the specific crystal plane of the group III nitride crystal is a (1-100) plane.

9. The seed substrate according to claim 6 , wherein a seed crystal positioned the nearest to an outer periphery of the substantial regular hexagonal region has the same shape as seed crystals in a center side of the hexagonal region.