Experimental evidence for charge state of 3H defect in diamond

The optical absorption of the 3H centre in diamond was studied at isochronal annealing in the temperature range of 370 to 620K for samples irradiated with electrons or neutrons. The undoped (concentration of substitutional nitrogen <1 ppm) and boron-doped (a few ppm B) CVD diamond films were produced by a microwave plasma CVD technique. It was found that in the undoped diamond the increase of the 3H absorption at the annealing temperature of 620K is accompanied with an increase of absorption by the negatively charged vacancy (V - ), whilst the neutral vacancy (V°) absorption is diminished. In contrast, in the B-doped diamond the absorption of both 3H and V° centres grew, and this occurred at a lower annealing temperature of 470K. The observed trends can be explained by the charge transfers between 3H and vacancy centres. This leads to the conclusion that the (3H)° centre is a donor, and the 2.462 eV absorption line belongs to the centre in the positively charged state, (3H) + .