Disorder effects of nitrogen impurities, irradiation-induced defects, andC13isotope composition on the Raman spectrum in synthetic Ibdiamond

For type-Ib diamond, we have experimentally studied the change in the Raman spectrum with the concentration of nitrogen impurities, the fluence of neutron irradiation and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ isotope composition, to look for phonon scattering due to these events. It has been found that the nitrogen impurities have no appreciable effect on the Raman spectrum in the concentration range up to 330 ppm, except for a small broadening. For neutron fluences above 7×${10}^{17}$ n/${\mathrm{cm}}^2$, a low energy shift of the Raman peak and a broadening occur simultaneously. Thermal recovery of these change starts at annealing temperatures below 300 °C and is achieved almost completely around 1000 °C. This fact implies that the phonon scattering is strongly enhanced by atoms displaced slightly from the normal sites as well as interstitials, but is less influenced by vacancies. The Raman intensity decreases abruptly at high neutron fluence and is partially restored by annealing at 1700 °C. The lack of full recovery of the Raman intensity on annealing is ascribed to absorption of the exciting light due to the formation of color centers. For ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ substitution, a deviation of the Raman energy from the virtual crystal model with a mean reduced mass is demonstrated, which expresses the contribution of the isotope substitution to the self-energy. Maxima in the energy deviation and broadening occur around 70% ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ composition. Empirical parameters describing the energy deviation have been obtained. The present results coincide well with those reported by Chrenko and Hass et al. © 1996 The American Physical Society.