Optical centres related to nitrogen, vacancies and interstitials in polycrystalline diamond films grown by plasma-assisted chemical vapour deposition

The authors have used cathodoluminescence spectroscopy to examine point defects present in polycrystalline diamond films grown by the decomposition of a methane-hydrogen mixture in a microwave plasma. For films grown with low methane concentrations (0.3%) the bright-blue luminescence is predominantly due to donor-accepted pair recombination, together with some weak zero-phonon lines. As the CH 4 concentration in the gas mixture is increased the cathodoluminescence spectra from the resulting films contain a number of additional zero-phonon lines. Some of these are unique to this type of diamond; other lines at 2.156 eV, 2.807 eV, 3.188 eV and 4.582 eV are associated with optical centres that have been studied in diamonds produced by high-pressure synthesis, and indicate that the diamond films contain carbon interstitials, nitrogen-vacancy and nitrogen-interstitial centres. The widths of the zero-phonon lines in the diamond films suggest that the material is heavily strained.