Effects of light on the "primed" state
of CVD diamond nuclear detectors
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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 |
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C. Manfredotti, E. Vittone, F. Fizzotti, A. Lo Giudice and C. Paolini |
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Experimental Physics Department, University of Torino, Torino, Italy |
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Keywords: CVD diamond, pumped state,
nuclear detector |
Abstract
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.