NITROGEN-RELATED DOPANT AND DEFECT STATES IN CVD DIAMOND

Subbandgap absorption of chemical-vapor-deposition diamond films, with nitrogen contents varying from 10 to 132 ppm has been explored by the constant-photoconductivity method (CPM), photothermal-deflection spec troscopy (PDS) and electron spin resonance (ESR). The spectra measured by PDS increase monotonically and are structureless with increasing p hoton energies indicating absorption due to amorphous carbon and graph ite. The CPM data show distinct features, with absorption bands at h n u=1.6, 4.0, and 4.7 eV in the nominally undoped film, and 2.4 and 4.7 eV in nitrogen-rich layers respectively. The CPM spectra of the doped films are comparable to photoconductivity data of synthetic Pb diamond . The defect densities involved increase with increasing nitrogen cont ent. From ESR, a vacancy-related defect density (g = 2.0028) is deduce d. Paramagnetic nitrogen (g = 2.0024) can be detected in the high-qual ity CVD layer or by illuminating the nitrogen-rich samples with photon energies larger than the band gap.