Boron doped diamond
View Patent ↗A layer of single crystal boron doped diamond produced by CVD and having a total boron concentration which is uniform. The layer is formed from a single growth sector, or has a thickness exceeding 100 μm, or has a volume exceeding 1 mm 3 , or a combination of such characteristics.
1. A layer of single crystal boron doped diamond produced by CVD wherein the total boron concentration is uniform, with a variation over the majority volume which is less than 50%, measured with a lateral resolution at each measurement point of less than 50 μm, wherein the majority volume represents at least 70% of the total volume of the layer, and wherein the layer has at least one of the following characteristics (i) to (iii):
(i) the layer is formed from a single growth sector,
(ii) the layer thickness exceeds 100 μm, and
(iii) the volume of the layer exceeds 1 mm 3 .
2. A diamond layer according to claim 1 wherein the variation over the majority volume is less than 20%.
3. A diamond layer according to claim 1 wherein the variation is measured with a lateral resolution at each measurement point of less than 30 μm.
4. A diamond layer according to claim 1 wherein the majority volume of the layer contains an uncompensated boron concentration greater than 1×10 14 atoms/cm 3 and less than 1×10 20 atoms/cm 3 .
5. A diamond layer according to claim 1 wherein the majority volume of the layer contains an uncompensated boron concentration greater than 1×10 15 atoms/cm 3 and less than 2×10 19 atoms/cm 3 .
6. A diamond layer according to claim 1 wherein the majority volume of the layer contains an uncompensated boron concentration greater than 5×10 15 atoms/cm 3 and less than 2×10 18 atoms/cm 3 .
7. A diamond layer according to claim 1 which has a hole mobility (μ h ) measured at 300K which exceeds
μ h =G× 2.1×10 10 (N h 0.52 )
for N h not exceeding 8×10 15 atoms/cm 3 (Equation (1)
μ h =G ×1×10 18 /N h
for N h greater than 8×10 15 atoms/cm 3 (Equation (2)
where N h is the concentration of holes, and G has a value greater than 1.1.
8. A diamond layer according to claim 7 wherein G has a value greater than 1.4.
9. A diamond layer according to claim 7 wherein G has a value greater than 1.7.
10. A diamond layer according to claim 7 wherein G has a value greater than 2.
11. A diamond layer according to claim 1 which has low or absent luminescent features at 575 and 637 nm, relating to N-V centres.
12. A diamond layer according to claim 1 wherein the ratio of each of the integrated nitrogen vacancy centre zero-phonon lines at 575 nm and 637 nm with the integrated intensity of the diamond Raman line at 1332 cm −1 when measured at 77 K with 514 nm Ar ion laser excitation, is less than 1/50.
13. A diamond layer according to claim 12 wherein the ratio is less than 1/100.
14. A diamond layer according to claim 12 wherein the ratio is less than 1/300.
15. A diamond layer according to claim 1 which has a Raman line width as measured at 300 K of less than 4 cm −1 FWHW under 514 nm Ar ion excitation.
16. A diamond layer according to claim 15 wherein the Raman line width is less than 3 cm −1 FWHW.
17. A diamond layer according to claim 15 wherein the Raman line width is less than 2.5 cm −1 FWHW.
18. A diamond layer according to claim 1 wherein the frequency distribution of uncompensated boron measurements taken by FTIR over a representative sample taken from the layer is such that 90% of the measurements vary by less than 50% of the mean.
19. A diamond layer according to claim 1 wherein the frequency distribution of uncompensated boron measurements taken by FTIR over a representative sample taken from the layer is such that 90% of the measurements vary by less than 30% of the mean.
20. A diamond layer according to claim 1 wherein the frequency distribution of the BE taken over any representative surface of the layer or a sample taken from the layer is such that 90% of the measurements vary by less than 50% of the mean.
21. A diamond layer according to claim 1 wherein the frequency distribution of the BE taken over any representative surface of the layer or a sample taken from the layer is such that 90% of the measurements vary by less than 30% of the mean.
22. A diamond layer according to claim 1 wherein the frequency distribution of FE measurements taken over any representative surface of the layer or sample taken from the layer is such that 90% of the measurements vary by less than 50% of the mean.
23. A diamond layer according to claim 1 wherein the frequency distribution of FE measurements taken over any representative surface of the layer or sample taken from the layer is such that 90% of the measurements vary by less than 30% of the mean.
24. A diamond layer according to claim 1 wherein the majority volume represents greater than 85% of the total volume of the layer.
25. A diamond layer according to claim 1 wherein the majority volume represents greater than 95% of the total volume of the layer.
26. A diamond layer according to claim 1 wherein the layer is formed from a single growth sector which is one of the {100}, the {113}, the {111} and the {110} sectors.
27. A diamond layer according to claim 1 which has a thickness exceeding 500 μm.
28. A diamond layer according to claim 1 which has a volume exceeding 3 mm 3 .
29. A diamond layer according to claim 1 which has a volume exceeding 10mm 3 .
30. A diamond layer according to claim 1 which further contains nitrogen as a dopant.
31. A diamond layer according to claim 30 wherein nitrogen concentration is no greater than 1/5 that of the boron concentration.
32. A diamond layer according to claim 30 which contains a nitrogen concentration of less than 1/50 that of the boron concentration.
33. A diamond layer according to claim 1 , wherein the layer has at least characteristic (i).
34. A diamond layer according to claim 1 , wherein the layer has at least characteristic (ii).
35. A diamond layer according to claim 1 , wherein the layer has at least characteristic (iii).
36. A diamond body in which a diamond layer according to claim 1 forms a layer or region thereof.
37. An element produced from a diamond layer according to claim 1 or from a diamond body according to claim 36 .
38. A diamond body according to claim 36 or a diamond layer according to claim 1 in the form of a gemstone.
39. A diamond layer according to claim 2 wherein the variation is measured with a lateral resolution at each measurement point of less than 30 μm.
40. A method of producing a layer of single crystal boron doped diamond including the steps of providing a diamond substrate having a surface which is substantially free of crystal defects, providing a source gas, such source gas including a source of boron, dissociating the source gas and allowing homoepitaxial diamond growth on the surface which is substantially free of crystal defects, wherein said layer is that defined in claim 1 .
41. A method according to claim 40 wherein the source gas has nitrogen added to it in an amount suitable to control the morphology developed by the growing single crystal diamond.
42. A method according to claim 41 wherein the nitrogen addition to the source gas is greater than 0.5 ppm and less than 10000 ppm.
43. A method according to claim 41 wherein the nitrogen addition to the source gas is greater than 1 ppm and less than 1000 ppm.
44. A method according to claim 41 wherein the nitrogen addition to the source gas is greater than 3 ppm and less than 200 ppm.
45. A method according to claim 40 wherein the density of surface etch features related to defects on the surface on which diamond growth occurs is below 5×1O 3 /mm 2.
46. A method according to claim 40 wherein the density of surface etch features related to defects on the surface on which diamond growth occurs is below 10 2 /mm 2.
47. A method according to claim 40 wherein the surface on which diamond growth occurs is subjected to a plasma etch prior to diamond growth.
48. A method according to claim 40 wherein the diamond growth occurs on a {100}, {11O}, {113 } or {111} surface.
49. A method according to claim 41 wherein the boron source is B 2 H 6 .