Optical detection of defect centers in CVD diamond

Results of an extensive study of defect centers in chemical vapor deposited (CVD) diamond by optical transmittance, photoconductivity, photoluminescence (PL) and PL excitation (PLE) techniques are reported. Oscillatory behavior in PLE spectra for the silicon-vacancy center is observed and utilized to deduce E-C -2.05 eV as the optical ionization threshold for this center. A threshold at this energy is also seen in optical absorption spectra. It is shown that the IR absorption band at 800 cm(-1) due to SI-C vibrations can originate from Si-C bonds inside a diamond film, but not at the film-substrate interface. It is suggested that the increase in amorphous carbon (a-C) related defects tends to pin the surface Fermi level position around E-V +1 eV level, creating potential barriers across a polycrystalline diamond film, while nitrogen doping raises the bulk Fermi level position towards the conduction band. Therefore, variations in a-C and nitrogen contents can affect the population of defect levels in CVD diamond, which may lead to erroneous conclusions about the changes in the concentration of those centers on the basis of absorption or luminescence results. (C) 2000 Elsevier Science S.A. All rights reserved.