Intrinsic and extrinsic cathodoluminescence from single-crystal diamonds grown by chemical vapour deposition

Abstract

The authors have analysed the cathodoluminescence spectra from single-crystal diamonds grown by the decomposition of a methane-hydrogen mixture in a microwave plasma. Crystals grown using methane concentrations of <or approximately=1% exhibit 'edge emission' at around 5.3 eV due to the recombination of free excitons in association with momentum-conserving phonons. When the CH4 concentration is increased to 2% the edge emission becomes relatively weak, implying a degradation of crystal quality. All the diamonds exhibit bright blue luminescence in the visible spectral region due to donor-acceptor pair recombination. An emission line at 2.985 eV may be the N3 zero-phonon line which is commonly observed in natural diamonds; other emission lines are unique to these diamonds prepared by chemical vapour deposition. The widths of the zero-phonon lines suggest that the material is heavily strained.