Optical defect centers and surface morphology of diamond single crystals grown by chemical vapor deposition

A study was performed on the optical defect centers and surface morphology of isotopically enriched layers grown on diamond anvils by microwave plasma chemical vapor deposition for applications as designer diamond anvils in high-pressure diamond anvil cell devices. Various mixtures of methane isotopes were used to grow homoepitaxial diamond with 13 C molar fractions of 0.01, 0.41, 0.83, and 0.99 as determined from Raman spectroscopy. Defect centers were studied at temperatures between 80 K and 320 K using micro-photoluminescence spectroscopy with an argon ion and krypton laser excitation source. The defect spectra were dominated by zero phonon lines (ZPL) from nitrogen-related defect centers at nominal energies of 1.945 eV (640 nm defect) and 2.156 eV (575 nm defect), especially for the non-(100) surfaces. Polished (100) surfaces fluoresced weakly. ZPLs at 1.77 eV and 1.68 eV were observed, but not for all isotopically mixed samples. The 1.77 eV ZPL appeared to be associated with the original diamonds, while the 1.68 eV ZPL is known to originate with silicon-based defects. Atomic force microscopy (AFM) of as-grown isotopically enriched layers showed rough growth steps in areas with surface roughness of 100 nm and smooth areas with surface roughness of a few nanometers. This study indicates that (100) polished surfaces of isotopically enriched designer diamonds with low concentration of nitrogen defect centers can be fabricated for a variety of applications in high pressure research. A separate study was performed on the growth of large crystals by chemical vapor deposition. These experiments included the effect of methane concentration, oxygen addition, and nitrogen addition on the growth rate and surface morphology. It was found that the largest impact on the surface morphology was the microwave power density, which changed the surface from a hillock-type growth to a step-flow growth. The surface defects were studied using an AFM and optical imaging, while the optical defects were analyzed using photoluminescence spectrometry. A crystal of 3mm in size was grown in a period of 60 hours.