Crystalline perfection of high purity synthetic diamond crystal

Crystalline quality of high purity synthetic diamond crystals (type IIa) with impurities less than 0.1 ppm grown by a temperature gradient method under high-pressure and high-temperature has been investigated in detail, The crystal defects and internal strains of the synthetic type IIa diamonds were studied by double-crystal X-ray rocking curve measurement, polarizing microscopy, X-ray topography and Raman spectroscopy. The synthetic type IIa diamonds were found to have high crystalline quality with fewer crystal defects, less internal strain and less variation in defects among crystals than those of natural diamonds or synthetic type Ib diamonds. However, in the synthetic type IIa diamond crystal some line and plane defects were observed. It was found that by using strain-free and low defect crystals for the seeds, the line defects (dislocation bundles) could be removed, thereby improving the crystalline quality of the synthetic type IIa diamonds.