Influence of damage caused by Kr ions and neutrons on electrical properties of silicon detectors

In this paper, new measurements of physical properties of high-resistivity silicon, used in high-energy detectors, are presented. The obtained data contribute to the understanding of the causes which damage the electronic characteristics of the detection systems under irradiation of neutrons and ionized particles (Kr). The Hall effect coefficient (RH) and resistivity (ρ) measurements as a function of temperature (T), for non-irradiated and irradiated by neutrons and Kr ions, were performed. The measurements of the Hall coefficient and resistivity of non-irradiated samples and irradiated at neutron fluences (Φ⩽9.9×1010 n/cm2) and Kr (Φ⩽7.5×108 Kr/cm2), have shown that the obtained characteristics, RH(T) and ρ(T), are of the same shape as those known for a silicon single crystal. A slight difference of the slope of ln ρ∼ln T, for neutron- and a large difference for Kr ion irradiation as compared with that of non-irradiated samples, was observed. On increasing the irradiation to Φ larger than the value indicated above, for neutrons and Kr ions, important changes in the physical properties were observed. The resistivity increases with increasing Φ, up to a value of the same order with intrinsic silicon (ρ∼105 Ω cm), for both neutron and Kr ion irradiation. The values of RH increase with increasing Φ up to a fluence, for which a change of sign, from negative to positive, occurs. The variation of values of RH and ρ as a function of Φ, for neutrons and Kr ions, is similar, but the characteristics RH(Φ) and ρ(Φ), are displaced. Therefore, larger values of Φ are needed in order to obtain the same values of ρ as those for Kr ion irradiation. The dependence on T of electrical parameters of samples, irradiated at Φ⩾9.9×1010 n/cm2 (neutrons) and Φ⩾7.5×108 Kr/cm3 (ions), cannot be explained, considering the usual theoretical relations. The results, obtained in these experiments, have shown a change of mechanism of conduction due to the damaged regions, where localized levels are created, which are the main cause of the deviation of the electrical characteristics of the detectors from that of the usual non-irradiated device. These studies enable to explain the changes of the measured electrical properties, of the detectors under irradiation.