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Radiation damage in room temperature detectors
|Anna Cavallini , A. Castaldini , B. Fraboni , L. Polenta , L. Rigutti
University of Bologna, Department of Physics, Viale Berti Pichat 6/2, Bologna, Italy
Radiation damage strongly affects the performance of room temperature detectors. The interaction of ionizing particles often causes an increase in leakage current, a degradation of energy resolution and a shift of the peak position due to the lost charge collection efficiency. The origin of these effects is linked to the presence of electrically active defects that intervene in the charge carrier transport properties. We have carried out a systematic study on the effects of the exposure to electrons, gamma-rays, protons and neutrons of various energies and doses/fluences on detectors based on different materials: Cd0.9Zn0.1Te, CdTe:Cl , SiC and GaAs. All the above-cited materials have peculiar characteristics that correspond to pros and cons in different applications, and also have very different fallout on device costs and environmental electronics. This paper addresses the analysis of the modifications induced on each of these materials by different types of radiation and the study is performed from the viewpoint of the microscopic defects that are generated/modified by particle radiation and of the electronic levels associated to them. Such a rather challenging task will be dealt with by studying the charge carrier transport properties using gamma spectroscopy analyses (57Co and 241Am), dark current and capacitance-voltage measurements, as well as junction spectroscopy investigations (DLTS and PICTS). The results obtained by utilizing these tools have to be cross-correlated if we are to disentangle the effects of the various defects. Radiation induced defects will be shown to play a paramount role in the material compensation process, which in turn determines the electric field distribution across the detector. Indeed, the correlation between particular defects and transport properties is sometimes evident while in other cases is far from being satisfied. It is also reported that "large density of specific defects" not always mean "low detector efficiency": in CdZnTe only some defects are really effective as lifetime killer and in SiC a ionising radiation generates a very large amount of defects with no appreciable change in the detector efficiency. That comparison will, hopefully, help better understanding and improvement of devices.
Presentation: invited oral at NATO Advanced Research Workshop, by Anna Cavallini
See On-line Journal of NATO Advanced Research Workshop
Submitted: 2004-08-04 22:01 Revised: 2009-06-08 12:55