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, photoluminescen ce (PL) and PL excitation (PLE) techniques are reported. Oscillatory behavi or in PLE spectra for the silicon-vacancy center is observed and utilized t o 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 i s shown that the IR absorption band at 800 cm(-1) due to SI-C vibrations ca n originate from Si-C bonds inside a diamond film, but not at the film-subs trate 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 f ilm, while nitrogen doping raises the bulk Fermi level position towards the conduction band. Therefore, variations in a-C and nitrogen contents can af fect the population of defect levels in CVD diamond, which may lead to erro neous conclusions about the changes in the concentration of those centers o n the basis of absorption or luminescence results. (C) 2000 Elsevier Scienc e S.A. All rights reserved.