The effect of HPHT treatment on the spectroscopic features of type IIb synthetic diamonds

Abstract

The effect of high pressure high temperature treatment on the spectroscopic features of boron-doped type IIb synthetic diamonds has been studied. Synthetic HPHT diamond crystals with different concentrations of boron acceptors were annealed at temperatures in the range 1800–2650 °C under a stabilizing pressure of 7–7.5 GPa. Fourier-transform infra-red absorption spectroscopy and cathodoluminescence were applied to study the effect of the annealing. We found that for annealing temperatures up to 2650 °C, the IR absorption features related to neutral boron acceptors did not change in intensity, demonstrating that single substitutional boron was not affected by the treatment. This finding is in good agreement with the recent first-principle calculations of Goss and Briddon (Phys. Rev. B 73 (2006) 085207) predicting very high activation energies for migration of substitutional boron in the diamond lattice. For diamonds with boron concentration of about 1 ppm, it was found that annealing at 2650 °C for 1 h produced an intense CL emission band peaking at 2.85 eV, which is known to be related to dislocations. It was suggested that dislocations in the studied boron-doped diamonds were formed due to plastic deformation occurred during anneals.