Gap density of states in CVD diamond films from photoconductivity and photoluminescence data

Spectral photoconductivity (PC) and photoluminescence (PL) have been used to investigate the nature and distribution of defect states in CVD-grown polycrystalline diamond films. PC measurements at 300 K reveal an onset close to 1 eV and two broad bands peaking at 2.2 and 3.6 eV, which are mainly attributed to photoionization of impurities, Transitions between localized energy levels are responsible for a PL vibronic band peaking at 1.68 eV. Excitation spectra monitored at this energy exhibit at 77 K a sharp resonance at 1.95 eV. Starting from these results a possible picture of the defect density distribution is suggested and a simple model for the electronic structure of the 1.68 eV optical center is proposed. (C) 1997 Elsevier Science S.A.