High colour diamond layer
View Patent ↗A method of producing CVD diamond having a high color, which is suitable for optical applications, for example. The method includes adding a gaseous source comprising a second impurity atom type to counter the detrimental effect on colour caused by the presence in the CVD synthesis atmosphere of a first impurity atom type. The described method applies to the production of both single crystal diamond and polycrystalline diamond.
1. A method of forming a CVD diamond, the method comprising:
(i) providing a substrate;
(ii) providing a CVD synthesis atmosphere in which there exists a gas comprising nitrogen at a concentration greater than 300 ppb, calculated as molecular nitrogen; and
(iii) adding into the CVD diamond synthesis atmosphere a gas comprising boron or silicon, wherein the boron or silicon is added in a controlled manner into the CVD diamond synthesis atmosphere to reduce a detrimental effect on color of the single crystal CVD diamond caused by nitrogen so as to produce a single crystal CVD diamond in which a majority volume of at least 80% of the single crystal CVD diamond has at least one of the following features (a) to (e):
(a) an absorption spectrum measured at room temperature such that the color of a standard 0.5 ct round brilliant would be better than K on the Gemological Institute of American (GIA) gem diamond color scale;
(b) an absorption coefficient at 270 nm measured at room temperature which is less than 2.9 cm −1 ;
(c) an absorption coefficient at 350 nm measured at room temperature which is less than 1.5 cm −1 ;
(d) an absorption coefficient at 520 nm measured at room temperature which is less than 0.45 cm −1 ; and
(e) an absorption coefficient at 700 nm measured at room temperature which is less than 0.18 cm −1 ,
wherein the single crystal CVD diamond has a thickness of greater than 0.1 mm, wherein a concentration of nitrogen in the majority volume of the single crystal CVD diamond is greater than 5×10 15 atoms/cm 3 , and wherein a concentration of boron or silicon in the majority volume of the single crystal CVD diamond is greater than 10 14 atoms/cm 3 .
2. The method of claim 1 , wherein silicon is added into the CVD diamond synthesis atmosphere.
3. The method of claim 2 wherein the concentration of nitrogen in the majority volume of the diamond layer is less than or equal to 2×10 17 atoms/cm 3 and the concentration of silicon in the majority volume of the diamond layer is less than or equal to 2×10 18 atoms/cm 3 .
4. The method of claim 2 wherein the ratio of the concentration of nitrogen to the concentration of silicon in the majority volume of the diamond layer is from 1:20 to 20:1.
5. The method of claim 2 wherein the gas comprising nitrogen is present in the synthesis atmosphere at a concentration of greater than 300 ppb and the gas comprising silicon is present in the synthesis atmosphere at a concentration of greater than 10 ppb.
6. The method of claim 1 , wherein boron is added into the CVD diamond synthesis atmosphere.
7. The method of claim 6 wherein the ratio of the concentration of nitrogen to the concentration of boron in the majority volume of the diamond layer is from 1:2 to 2:1.
8. The method of claim 6 wherein the gas comprising nitrogen is present in the synthesis atmosphere at a concentration of greater than 300 ppb and the gas comprising boron is present in the synthesis atmosphere at a concentration of greater than 0.5 ppb.
9. The method of claim 1 wherein the produced CVD diamond layer has an increased normalized free exciton intensity compared to a method where the second gas comprising a second impurity type atom is not added.
10. The method of claim 1 wherein the produced CVD diamond layer has an increase in carrier mobility, carrier lifetime and/or charge collection distance compared to a method where the second gas comprising a second impurity type atom is not added.
11. The method of claim 1 wherein the synthesis atmosphere comprises a concentration of the gas comprising nitrogen which has not been added deliberately of greater than 300 ppb.
12. The method of claim 1 wherein the gas comprising nitrogen is not added in a controlled manner.
13. The method of claim 1 wherein the method comprises one or more of the following features:
(1) the substrate is a diamond substrate having a surface which is substantially free of crystal defects such that a revealing plasma etch would reveal a density of surface etch features related to defects below 5×10 3 /mm 2 ;
(2) the duration of the synthesis of the single crystal diamond layer is at least 50 hours; and
(3) the substrate comprises multiple separated single crystal diamond substrates.
14. The method of claim 1 wherein the CVD diamond layer is a single crystal, and wherein the majority volume of the diamond layer has at least one of the following features:
a) an absorption spectrum measured at room temperature such that the colour of a standard 0.5 ct round brilliant would be better than K;
b) an absorption coefficient at 270 nm measured at room temperature which is less than 1.9 cm −1 ;
c) an absorption coefficient at 350 nm measured at room temperature which is less than 0.90 cm −1 ;
d) an absorption at 520 nm of less than 0.30 cm −1 ; or
e) an absorption at 700 nm of less than 0.12 cm −1 .
15. The method of claim 1 wherein the CVD diamond layer is a single crystal and wherein the diamond layer is formed into a gemstone having three orthogonal dimensions greater than 2 mm, where at least one axis lies either along the <100> crystal direction or along the principle symmetry axis of the gemstone.
16. A CVD diamond layer produced by the method of claim 1 .
17. An optical element comprising the CVD diamond layer produced according to the method of claim 1 .
18. An electrical or electronic element comprising the CVD diamond layer produced according to the method of claim 1 .
19. A CVD diamond layer produced according to the method of claim 1 having a thickness greater than 0.1 mm.
20. A CVD single crystal diamond layer produced according to the method of claim 1 in the form of a gemstone.
21. A CVD single crystal diamond layer according to claim 20 having three orthogonal dimensions greater than 2 mm, wherein at least one axis lies along the <100> crystal direction or along the principle symmetry axis of the gemstone.
22. A CVD single crystal diamond layer according to claim 20 having a clarity of at least SH on the GIA gem grading scale.
23. A single crystal CVD diamond layer, wherein a majority volume of at least 80% of the single crystal diamond layer has at least one of the following features (a) to (e):
(a) an absorption spectrum measured at room temperature such that the color of a standard 0.5 ct round brilliant would be better than K on the Gemological Institute of American (GIA) gem diamond color scale;
(b) an absorption coefficient at 270 nm measured at room temperature which is less than 2.9 cm −1 ;
(c) an absorption coefficient at 350 nm measured at room temperature which is less than 1.5 cm −1 ;
(d) an absorption coefficient at 520 nm measured at room temperature which is less than 0.45 cm −1 ; and
(e) an absorption coefficient at 700 nm measured at room temperature which is less than 0.18 cm −1 ,
wherein the single crystal CVD diamond has a thickness of greater than 0.1 mm, wherein a concentration of nitrogen in the majority volume of the single crystal CVD diamond is greater than 5×10 15 atoms/cm 3 , and wherein a concentration of boron or silicon in the majority volume of the single crystal CVD diamond is greater than 10 14 atoms/cm 3 .
24. The CVD diamond layer of claim 23 wherein the majority volume of the diamond layer comprises from 10 15 to 2×10 18 atoms/cm 3 of silicon.
25. The CVD diamond layer of claim 23 wherein silicon is present in the single crystal CVD diamond layer.
26. The CVD diamond layer of claim 23 wherein the layer has a thickness of greater than 1 mm.
27. The CVD diamond layer of claim 23 wherein the layer has a birefringence of less than 1×10 −3 over a volume greater than 0.1 mm 3 .
28. The CVD diamond layer of claim 23 wherein the diamond layer is a single crystal.