Process for producing an epitaxial layer of galium nitride

1. A method of manufacturing a low defect density GaN material comprising at least two steps of growing epitaxial layers of GaN with differences in growing conditions,

a. a first step of growing an epitaxial layer GaN on an epitaxially competent layer under first growing conditions selected to induce island features formation, wherein said first step of growing is accomplished without the use of a mask, followed by

b. a second step of growing an epitaxial layer of GaN under second growing conditions selected to enhance lateral growth until coalescence,

wherein a temperature of the said second growing conditions is higher than a temperature of the said first growing conditions, and

wherein the temperature of the first growing conditions is below about 950° C.

2. The method of claim 1 , wherein the temperature of the first growing conditions is comprised between about 500° C. and about 950° C.

3. The method of claim 1 , wherein the temperature of the second growing conditions is above 1000° C. to about 1080° C.

4. The method of claim 1 , wherein the temperature of the second growing conditions is comprised between about 1015° C. and about 1020° C.

5. The method of claim 1 , wherein the temperature of the second growing conditions is above 1060° C. to about 1080° C.

6. The method of claim 1 , wherein the temperature of the second growing conditions is about 1080° C.

7. The method of claim 1 , wherein the temperature of the first growing conditions is comprised between about 900° C. and about 950° C. and the temperature of the second growing conditions is comprised between about 1015° C. and 1020° C.

8. The method of claim 1 , wherein the temperature of the first growing conditions is comprised between 450° C. and 600° C. and the temperature of the second growing conditions is about 1080° C.

9. The method of claim 1 , wherein oxygen is added to a vapour phase of the first growing conditions to induce island features formation.

10. The method of claim 9 , wherein the oxygen is excluded from the second growing conditions to induce enhanced lateral growth.

11. The method of claim 1 , wherein oxygen pressure in a vapour phase of the first growing conditions is above oxygen pressure in a vapour phase of the second growing conditions.

12. The method of claim 1 , wherein the first growing conditions comprise a temperature of between 900° C. and 950° C. and an oxygen pressure Pose in a vapour phase such that the ratio Pox/P GaCl greater than 0.0005, and the second growing conditions comprise a temperature of between about 1000° C. and 1050° C. without oxygen in a vapour phase.

13. The method of claim 1 , wherein Mg and/or Sb is added to a vapour phase of the second growing conditions.

14. The method of claim 1 , wherein the epitaxially competent layer comprises a substrate that comprises a base layer and an upper crystalline layer compatible with the growth of a nitride crystal.

15. The method of claim 14 , wherein the upper crystalline layer is chosen among the group consisting of sapphire, spinel, GaN, AlN, GaAs, Si, SiC (6H-,4H-,3C-), LiAlO2, LiGaO2, ZrB2, HfB2 and mixtures thereof.

16. The method of claim 15 , wherein the upper crystalline layer is an AlN or GaN crystalline material.

17. The method of claim 14 , wherein the base layer is a sapphire layer.

18. The method of one of claim 14 , wherein the substrate comprises at least one sacrificial layer between the base layer and the upper crystalline layer.

19. The method of claim 1 , wherein the low defect density GaN material is a single crystal.

20. The method of claim 19 , wherein the single crystal has a thickness of at least 1 μm.

21. The method of claim 19 , wherein the single crystal has a thickness ranging from 100 μm to 10 cm.

22. The method of claim 19 , wherein the single crystal has a thickness ranging from 500 μm to 3 mm.

23. The method of claim 1 , wherein the low defect density GaN material is removed from the epitaxially competent layer.

24. The method of claim 23 , comprising a further step of wafering of the low defect density GaN material.

25. A free standing GaN obtainable by a method of claim 1 , wherein the measured lifetime of time resolved photoluminescence (TPRL) of the PL peak corresponding to electron-hole plasma under high excitation 0.4 mJ/cm 2 at room temperature is higher than 400 ps.

26. The free standing GaN according to claim 25 , where the threading dislocation (TD) densities are 10 6 cm −2 .

27. The method of claim 1 , wherein the temperature of the first growing conditions is comprised between 600° C. and 900° C. and the temperature of the second growing conditions is about 1020° C. to 1080° C.