Photoionization cross-section of dominant defects in CVD diamond

Main defects in the gap of free standing optical-quality CVD diamond have been investigated with the help of electron paramagnetic resonance (EPR) and the constant photocurrent method (CPM). The EPR and CPM measurements reveal well-defined substitutional nitrogen defect state in the gap with a photoionization energy E-i = 2.2 eV. Another set of defect states comes from the presence of hydrogen. CPM shows a significant effect of the hydrogenation, which generates a bulk defect with a photoionization energy E-i = 1.2 eV in the gap of CVD diamond. Annealing studies after hydrogenation show that this defect is not responsible for p-type surface conductivity of diamond, because it is thermally stable even at 930 degrees C but the surface conductivity vanishes at much lower temperatures. The EPR resonances in the g congruent to 2.0028 region are also investigated as a function of hydrogenation and oxidation. (C) 1999 Elsevier Science S.A. All rights reserved.