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 spectroscopy (PDS) and electron spin resonance (ESR). The spectra measured by PDS increase monotonically and are structureless with increasing photon energies indicating absorption due to amorphous carbon and graphite. The CPM data show distinct features, with absorption bands at hν=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 Ib diamond. The defect densities involved increase with increasing nitrogen content. From ESR, a vacancy-related defect density (g=2.0028) is deduced. Paramagnetic nitrogen (g=2.0024) can be detected in the high-quality CVD layer or by illuminating the nitrogen-rich samples with photon energies larger than the band gap.