Process for the production of synthetic diamond

A method for the production of a strain-free synthetic diamond single crystal by the temperature gradient method, said diamond having a Raman spectrum peak of 1332 to 1333 cm.sup.-1, the FWHM of which peak, when measured by means of an apparatus for Raman spectroscopic analysis with a resolving power of at most 1 cm.sup.-1, is at most 2 cm.sup.-1, and having an X-ray diffraction rocking curve, the FWHM of which is at most 6 arcseconds, and in which nitrogen atoms and boron atoms are contained in the crystal and the difference between the number of the nitrogen atoms and that of the boron atoms is at most 1.times.10.sup.17 atoms/cm.sup.3, and wherein the nitrogen content is at most 10 ppm and the boron content is at most 1 ppm and wherein there is employed in said method a carbon source having a boron content of at most 10 ppm and a solvent metal having a boron content of at most 1 ppm, said method comprising:

• arranging the carbon source, solvent metal and seed crystal in this order,
• adding a nitrogen getter which is at least one member selected from the group consisting of Group IVa and Va elements of the Periodic Table and an element capable of preventing formation of a carbide of at least one member selected from the group consisting of Group IVb and Vb elements of the Periodic Table to the solvent metal, the solvent metal including elements selected from the group consisting of Cu, Ag, Au, Zn or Cd, which elements are capable of preventing the formation of a carbide of a Group IVa or Va element of the Periodic Table, and
• arranging a buffer material for stabilizing initial growth of the crystal between the solvent metal and the surface of the seed crystal, and
• wherein the diamond is synthesized at a high pressure and temperature at which the diamond is stable in said temperature gradient method in an apparatus including a sample section wherein the diamond is synthesized under said high pressure and temperature, followed by lowering the temperature and pressure in the sample section to room temperature and pressure, and wherein the lowering of the pressure in said sample section is performed at a temperature of 300 to 1000.degree. C.