HOMOEPITAXIAL C-13 DIAMOND FILMS STUDIED BY MICRO-RAMAN AND PHOTOLUMINESCENCE SPECTROSCOPY

Raman microscopy has been used to study C-13 and C-12/C-13 isotopically mixed homoepitaxial diamond films grown by chemical vapor deposition on natural diamond substrates. The measured dependencies of the frequency and the width of the first-order zone-center optic phonon line on the isotope composition agree well with those reported for diamond crystals synthesized under high pressure. To study the evolution of the epitaxial layer quality for a C-13 diamond film grown on a natural type IIa diamond substrate with an isotopic composition of almost pure C-12, micro-Raman spectroscopy has been performed on a polished cross section. The width of the zone-center phonon line is found to increase in the epitaxial layer from 2.6 up to 3.0 cm-1 with increasing distance from the film/substrate interface and is thus consistently larger than the linewidth of 2.5 cm-1 measured in the substrate. Two photoluminescence bands are observed in the epitaxial film centered at 2.16 and 2.21 eV. The 2.16 eV band, which has been attributed to emission from an interstitial nitrogen-vacancy complex, shows a pronounced maximum in intensity at the film/substrate interface indicating an enhanced nitrogen incorporation at the interface.