DISORDER EFFECTS OF NITROGEN IMPURITIES, IRRADIATION-INDUCED DEFECTS,AND C-13 ISOTOPE COMPOSITION ON THE RAMAN-SPECTRUM IN SYNTHETIC IB DIAMOND

For type-Ib diamond, we have experimentally studied the change in the Raman spectrum with the concentration of nitrogen impurities, the flue nce of neutron irradiation and C-13 isotope composition, to look for p honon scattering due to these events. It has been found that the nitro gen 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 7x10(17) n/cm(2), a low energy shift of the Ra man peak and a broadening occur simultaneously. Thermal recovery of th ese change starts at annealing temperatures below 300 degrees C and is achieved almost completely around 1000 degrees C. This fact implies t hat the phonon scattering is strongly enhanced by atoms displaced slig htly from the normal sites as well as interstitials, but is less influ enced by vacancies. The Raman intensity decreases abruptly at high neu tron fluence and is partially restored by annealing at 1700 degrees C. The lack of full recovery of the Raman intensity on annealing is ascr ibed to absorption of the exciting light due to the formation of color centers. For C-13 substitution, a deviation of the Raman energy from the virtual crystal model with a mean reduced mass is demonstrated, wh ich expresses the contribution of the isotope substitution to the self -energy. Maxima in the energy deviation and broadening occur around 70 % C-13 composition. Empirical parameters describing the energy deviati on have been obtained. The present results coincide well with those re ported by Chrenko and Hass et al.