Group III nitride crystal, crystal growth process and crystal growth apparatus of group III nitride

1. A crystal growth method of a group III nitride, comprising the steps of:

forming a melt mixture of an alkali metal and a group III element in a reaction vessel; and

growing a crystal of a group III nitride formed of said group III element and nitrogen from said melt mixture in said reaction vessel,

said step of growing said crystal of said group III nitride being conducted while controlling an increase rate of degree of supersaturation of a group III nitride component in said melt mixture in a surface region in the vicinity of a surface of said melt mixture, thereby suppressing formation of a polycrystalline aggregate on said surface region.

2. The method as claimed in claim 1 , wherein said group III nitride is grown at said surface region of said melt mixture.

3. The method as claimed in claim 1 , wherein said control of said change rate of degree of supersaturation of said group III nitride component is conducted by controlling a rate of increase of nitrogen concentration in said melt mixture in said surface region of the said melt mixture.

4. The method as claimed in claim 1 , wherein said step of growing said crystal of said group lii nitride comprises the step of introducing a substance containing nitrogen into said reaction vessel in the form of a gas,

said step of controlling the degree of supersaturation being conducted by conducting a step of controlling an increase rate of nitrogen concentration in said melt mixture in said surface region of said melt mixture,

said step of controlling said increase rate of nitrogen concentration in said melt mixture being conducted by controlling a pressure of said substance containing nitrogen.

5. The method as claimed in claim 4 , wherein said substance containing nitrogen is introduced into said reaction vessel after a temperature of said melt mixture has reached a specified crystal growth temperature for causing crystal growth of said group III nitride, such that the pressure of said substance containing nitrogen is increased with a controlled rate during a growth of said group III nitride.

6. The method as claimed in claim 4 , wherein said pressure of said substance containing nitrogen is held constant at the moment said group III nitride starts to crystallize.

7. The method as claimed in claim 1 , wherein said step of growing said crystal of said group III nitride comprises the step of introducing a gas of a substance containing nitrogen into said reaction vessel at a temperature in which crystal growth of said group III nitride is caused,

said step of introducing said gas being conducted such that a temperature of said melt mixture in said surface region is controlled at the time when said gas is introduced.

8. The method as claimed in claim 7 , wherein said gas is introduced into said reaction vessel with a controlled supply rate.

9. The method as claimed in claim 7 , wherein said gas is introduced into said reaction vessel with a controlled temperature.

10. The method as claimed in claim 1 , wherein said step of growing said crystal of said group III nitride is conducted such that said crystal forms a plate-like crystal.

11. The method as claimed in claim 1 , wherein said step of growing said crystal of said group III nitride is conducted such that said. crystal forms a columnar crystal.

12. The method as claimed in claim 1 , wherein said group III nitride is grown from a seed crystal.

13. The method as claimed in claim 1 , wherein said group III nitride crystal is grown in the vicinity of a surface of said melt mixture.

14. A crystal growth method of a group III nitride, comprising the steps of:

forming a melt mixture of an alkali metal and a group III element in a reaction vessel; and

growing a crystal of a group III nitride formed of said group III element and nitrogen from said melt mixture in said reaction vessel,

said step of growing said crystal of said group III nitride being conducted while controlling a ratio of said alkali metal and said group III element in said melt mixture, thereby suppressing formation of a polycrystalline aggregate on said surface region.

15. The method as claimed in claim 14 , wherein said step of growing said crystal of said group III nitride is conducted such that said crystal forms a plate-like crystal.

16. The method as claimed in claim 14 , wherein said step of growing said crystal of said group III nitride is conducted such that said crystal forms a columnar crystal.

17. The method as claimed in claim 14 , wherein said group III nitride is grown from a seed crystal.

18. The method as claimed in claim 14 , wherein said group III nitride crystal is grown in the vicinity of said melt mixture surface.

19. A crystal growth method of a group III nitride formed of a group III element and nitrogen, comprising the steps of:

forming a melt mixture in a reaction vessel from an alkali metal and a substance containing said group III element; and

growing a crystal of said group III nitride in said reaction vessel from said melt mixture and a substance containing at least nitrogen,

said step of growing said crystal being conducted by increasing a pressure of said substance containing nitrogen with increase of temperature of said melt mixture in said reaction vessel, thereby suppressing formation of a polycrystalline aggregate on said surface region.

20. The method as claimed in claim 19 , wherein said pressure of said substance containing nitrogen is increased by introducing said substance containing nitrogen into said reaction vessel from outside of said reaction vessel in accordance with increase of said temperature of said melt mixture.

21. The methood as claimed in claim 19 , wherein said pressure of said substance containing nitrogen is increased by introducing said substance containing nitrogen and further an inert gas into said reaction vessel from outside of said reaction vessel in accordance with increase of said temperature of said melt mixture.

22. The method as claimed in claim 19 , wherein said step of growing said crystal of said group III nitride comprises the steps of sealing said reaction vessel after introducing said substance containing nitrogen into said reaction vessel and increasing said temperature of said melt mixture to a predetermined crystal growth temperature.

23. The method as claimed in claim 22 , wherein said step of sealing said reaction vessel is conducted when said substance containing nitrogen is introduced into said reaction vessel with such an amount that a partial pressure of said substance containing nitrogen reaches a predetermined partial pressure when said temperature of said melt mixture has reached said predetermined crystal growth temperature.

24. The method as claimed in claim 19 , wherein said step of growing said crystal comprises the steps of sealing said reaction vessel after introducing said substance containing nitrogen and an inert gas into said reaction vessel and increasing said temperature of said melt mixture to said predetermined crystal growth temperature.

25. The method as claimed in claim 24 , wherein said step of sealing said reaction vessel is conducted when said substance containing nitrogen and said inert gas are introduced into said reaction vessel with such an amount that a partial pressure of said substance containing nitrogen and a partial pressure of said inert gas reach respective predetermined pressure values when said temperature of said melt mixture has reached said predetermined crystal growth temperature.

26. The method as claimed in claim 19 , wherein said step of growing said crystal being conducted such that said crystal forms a plate-like crystal.

27. The method as claimed in claim 19 , wherein said step of growing said crystal being conducted such that said crystal forms a columnar crystal.

28. The method as claimed in claim 19 , wherein said step of growing said crystal is conducted by using a seed crystal.

29. The method as claimed in claim 19 , wherein said group III nitride crystal is formed in the vicinity of a surface of said melt mixture.