Cathodoluminescence of defects in diamond films and particles grown by hot-filament chemical-vapor deposition.

Abstract

Point defects, impurities, and defect-impurity complexes in diamond particles and polycrystalline films were investigated by cathodoluminescence (CL) imaging and spectroscopy in a scanning electron microscope. The diamond films and particles were grown by hot-filament methane-hydrogen chemical-vapor deposition at several different temperatures; the nominal deposition temperature (${T}_{d}$) ranged from 600 to 850 \ifmmode^\circ\else\textdegree\fi{}C. Electron-beam energies used to excite the CL were 10--30 keV. By comparing the CL spectra to spectra of known defects in natural and synthetic diamond, the following luminescence centers were identified: (a) 2.156-eV center (zero-phonon line observed at 2.15\ifmmode\pm\else\textpm\fi{}0.01 eV) attributed to a nitrogen-vacancy complex; (b) 2.326-eV center (observed peak position at 2.32\ifmmode\pm\else\textpm\fi{}0.01 eV), also thought to be a nitrogen-vacancy complex; (c) violet-emitting center (observed peak position at 2.82\ifmmode\pm\else\textpm\fi{}0.01 eV), associated with dislocation line defects, whose atomic structure is uncertain; (d) 3.188-eV center (observed peak position at 3.189\ifmmode\pm\else\textpm\fi{}0.001 eV), attributed to interstitial nitrogen or a nitrogen--(carbon-interstitial) complex; (e) isolated neutral vacancy (denoted the general radiation center) with principal zero-phonon line at 1.673 eV (observed peak position at 1.675\ifmmode\pm\else\textpm\fi{}0.002 eV).The luminescence from each center displayed a different dependence on ${T}_{d}$ and film morphology, as follows: (a) 2.156-eV center, maximum at ${T}_{d}$=600 \ifmmode^\circ\else\textdegree\fi{}C, corresponding to a cubic crystal-growth habit; (b) 2.326-eV center, similar to (a); (c) 2.82-eV center, maximum at ${T}_{d}$=750 \ifmmode^\circ\else\textdegree\fi{}C, octahedral crystal-growth habit; (d) 3.188-eV center, maximum at 650 \ifmmode^\circ\else\textdegree\fi{}C, transition between cubic and octahedral crystal growth; (e) 1.673-eV center (neutral vacancy), observed only at 850 \ifmmode^\circ\else\textdegree\fi{}C, relatively indistinct crystal-growth habit. CL from center (d) was induced by extended exposure to the electron beam. CL imaging of large (\ensuremath{\sim}10-\ensuremath{\mu}m) crystalline particles suggests that centers (a) and (c) are located primarily near {100} faces; the dislocation-related center (c) appears to be slightly more confined to near-surface regions than center (a).