Photoionization measurement of deep defects in single-crystalline CVD diamond using the transient-current technique

Abstract

We have adopted the transient-current technique as a sensitive method to detect small concentrations of charged defects in diamond and to study its photoionization spectrum. It is found that ionized impurity concentrations in the interval ${10}^{9}--{10}^{13}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ can readily be detected in diamond. By continuously measuring the charge concentration, while illuminating the samples with monochromatic light, the evolution of the charge state of the dominating defect can be continuously monitored. We have obtained the photoionization cross-section spectrum from the dominant deep defect in single-crystalline chemical vapor deposition (CVD) diamond using this method. The photoionization spectrum exhibits an onset at photon energies above ${E}_{i}=2.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. It is also found that the defect is in the positively charged and acts as an electron trap. The observed spectrum can be attributed to the single substitutional nitrogen impurity.