CRYSTALLINE PERFECTION OF HIGH-PURITY SYNTHETIC DIAMOND CRYSTAL

Crystalline quality of high purity synthetic diamond crystals (type II a) with impurities less than 0.1 ppm grown by a temperature gradient m ethod under high-pressure and high-temperature has been investigated i n detail, The crystal defects and internal strains of the synthetic ty pe IIa diamonds were studied by double-crystal X-ray rocking curve mea surement, polarizing microscopy, X-ray topography and Raman spectrosco py. The synthetic type IIa diamonds were found to have high crystallin e quality with fewer crystal defects, less internal strain and less va riation in defects among crystals than those of natural diamonds or sy nthetic type Ib diamonds. However, in the synthetic type IIa diamond c rystal some line and plane defects were observed. It was found that by using strain-free and low defect crystals for the seeds, the line def ects (dislocation bundles) could be removed, thereby improving the cry stalline quality of the synthetic type IIa diamonds.