Paper 2002-02

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Effects of light on the "primed" state of CVD diamond nuclear detectors

Presented at Diamond 2001 12th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide , 2-7 September 2001, Budapest, Hungary and published in Diamond and Related Materials 11 (2002) 446-450

C. Manfredotti, E. Vittone, F. Fizzotti, A. Lo Giudice and C. Paolini

Experimental Physics Department, University of Torino, Torino, Italy
and  INFM (National Institute for Matter Physics), UdR Torino-University, Torino, Italy

Keywords: CVD diamond, pumped state, nuclear detector



Diamond radiation detectors produced by Chemical Vapour Deposition (CVD) have been extensively studied as nuclear detectors both for the application as tracking detectors in high energy physics experiments and for applications in nuclear industry domain. A meaningful measurement to characterise the performance of such devices is the evaluation of the charge collection distance (CCD), i.e. the mean distance the charge carriers travel before being trapped. It is well known that CCD increases with the absorbed dose (priming or pumping process). The priming of diamond is usually explained by the saturation of active traps in the diamond bulk, which are filled by charge carriers generated by the ionisation. However, such a primed state is metastable, i.e. the exposure to light can de-pumps diamond to its initial state. The analysis of "pumping" and "de-pumping" processes is then useful to explain trapping mechanisms and polarisation effects which limit the performances of diamond detectors.
This paper deals with an investigation of the "pumping" process on detector grade CVD diamond samples exposed to some doses of irradiation (X-rays or beta particles). Photoconductivity measurements carried out during monochromatic illumination as well as optical bleaching spectra of thermoluminescence glow curves highlight the passivation effects of some trap levels due to irradiation. A possible interpretation of these effects is presented and discussed, taking into account charge collection efficiency measurements carried out using Am-241 alpha particles.