Effect of nitrogen impurity on the dislocation structure of large HPHT synthetic diamond crystals

The real structure of the {111} sectors of large single synthetic diamond crystals with different nitrogen contents has been studied by the selective etching method: (1) nitrogen-gettered diamonds with nitrogen impurity content at a level of 1-2 ppm, (2) diamond crystals grown without additives with nitrogen impurity of 180-220 ppm and (3) diamonds nitrogen alloyed during growth up to the concentrations of 550-600 ppm. All diamond crystals have been grown by the temperature gradient method using the high pressure apparatus of “split-sphere” type (BARS) at T=1350 °C, P=5.7 GPa and (100) seed crystal. It is found that the density of dislocations increases from 85 cm−2 to 4.0×103 cm−2 and the total length of planar defects increases from 30 to 300 μm/cm2 as the nitrogen content in the crystals increases up to 600 ppm. It is shown that partial dislocations are the dominant dislocations (60-90%) in all the crystals studied. A proportion of perfect dislocations increases as the nitrogen content in crystals, and correspondingly, the dislocation density increase. Possible causes for the increase of the extended defects density in the synthetic diamond crystals with the nitrogen impurity concentration rise are discussed.