The effects of nitrogen impurity on the radiation detection properties of synthetic diamond

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Abstract
This contribution examines the influence of nitrogen impurity on the radiation detecting properties of synthetic diamonds. The relatively low sensitivity of the commonly available synthetic diamonds, when used as dosimeters/detectors, is attributed to the presence of nitrogen. A systematic decrease of the nitrogen level shows an increase in the radiation detection sensitivity of these crystals, and below the 25–50 ppm level the increase is even steeper. Experimental evidence strongly suggests that the nitrogen, which is generally accepted to appear in synthetic diamond in dispersed paramagnetic form, not only acts as a radiationless recombination centre for charge carriers (with an estimated hole capture cross section of ≈10−12 cm2), but also affects the amount of traps formed in the synthesis of diamonds. This dual role of nitrogen which is suggested by the accumulated data is found to be consistent with a two-state model that is composed of a trapping and a recombination centre.