Defect mapping of a synthetic diamond single crystal by cathodoluminescence spectroscopy

Cathodoluminescence (CL) spectroscopy in a scanning electron microscope was used to identify and to map the spatial distribution of luminescent defects in a synthetic diamond single crystal. Several defect CL bands were observed in the 1.5-3.5 eV region: (i) a band with a zero-phonon line at 2.156 eV, attributed to a center containing nitrogen and atomic vacancies; (ii) a broadband centered at ∼2.2 eV, tentatively attributed to a boron-containing center; (iii) a doublet line at 2.33 eV, attributed to a nitrogen-containing center; (iv) a zero-phonon line at 2.555 eV, attributed to a nickel-containing center; (v) a broadband centered at ∼2.85 eV, attributed to a dislocation-related center; and (vi) a zero-phonon line at 3.188 eV, attributed to a center containing nitrogen and a carbon interstitial. Lines due to free and acceptor-bound excitons were observed in the 5.0-5.4 eV region. The spatial variation of the CL was examined in the vicinity of regions of relatively high dislocation density (∼10⁶ dislocations cm⁻²), which had been found in a previous x-ray diffraction imaging experiment. A quantitative analysis was made of the spatial variation of the band intensities. Upon moving from a relatively defect-free region to the center of a high dislocation density region, the intensities of defect bands (i) and (v) increased by very large factors (these bands were observed only within the high dislocation density regions); the intensity of defect band (vi) increased by a factor of ∼2; the acceptor-bound exciton intensity increased by a factor of 1.3; the intensities of defect bands (ii)-(iv) decreased by a factor of ∼2; and the free exciton intensity decreased by a factor of ∼7.5.