Photoconductive spectroscopy of diamond grown by chemical vapor deposition

Abstract

The photoconductivity of diamonds grown by chemical vapor deposition has been studied in the near infrared and visible spectral regions. The dominant photoconductive response has a threshold at approximately 1.5 eV. There is additional sharp structure in the region extending 165 meV to higher energy from the threshold, where 165 meV is the energy of the longitudinal optical (LO) phonon in diamond. It has also been found that there are minima in the photoconductivity spectrum at energies which are multiples of the energy of the LO phonon from the threshold energy. These minima have been associated with the decay of carriers to the bottom of the band by rapid emission of LO phonons. The optical absorption spectra of these diamonds show previously undocumented, sharp lines between 1.3 and 1.5 eV. These features are due to absorption to excited states of the same defect which is giving rise to the photoconductivity threshold at 1.5 eV. The sharp structure in the one-phonon region of the photoconductivity spectrum has been associated with capture to these excited states by the emission of LO phonons. Similar structure in the same region of the absorption spectrum has been attributed to Fano resonances—interference effects caused by the interaction of bound states with a continuum of states