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 co ntribute to the understanding of the causes which damage the electronic cha racteristics of the detection systems under irradiation of neutrons and ion ized particles (Kr). The Hall effect coefficient (R-H) and resistivity (rho ) measurements as a function of temperature (T), for non-irradiated and irr adiated by neutrons and Kr ions, were performed. The measurements of the Ha ll coefficient and resistivity of non-irradiated samples and irradiated at neutron fluences (Phi less than or equal to 9.9 x 10(10) n/cm(2)) and Kr (P hi less than or equal to 7.5 x 10(8) Kr/cm(2)), have shown that the obtaine d characteristics, R-H(T) and rho(T), are of the same shape as those known for a silicon single crystal. A slight difference of the slope of In rho si milar to In T, for neutron- and a large difference for Kr ion irradiation a s compared with that of non-irradiated samples, was observed. On increasing the irradiation to Phi larger than the value indicated above, for neutrons and Kr ions, important changes in the physical properties were observed. T he resistivity increases with increasing Phi, up to a value of the same ord er with intrinsic silicon (rho similar to 10(5) Omega cm), for both neutron and Kr ion irradiation. The values of R-H increase with increasing Phi up to a fluence, for which a change of sign, from negative to positive, occurs . The variation of values of R-H and rho as a function of Phi, for neutrons and Kr ions, is similar, but the characteristics R-H(Phi) and rho(Phi), ar e displaced. Therefore, larger values of Phi are needed in order to obtain the same values of shape as those for Kr ion irradiation. The dependence on T of electrical parameters of samples, irradiated at Phi greater than or e qual to 9.9 x 10(10) n/cm(2) (neutrons) and Phi greater than or equal to 7. 5 x 10(8) Kr/cm(3) (ions), cannot be explained, considering the usual theor etical relations. The results, obtained in these experiments, have shown a change of mechanism of conduction due to the damaged regions, where localiz ed levels are created, which are the main cause of the deviation of the ele ctrical characteristics of the detectors from that of the usual non-irradia ted device. These studies enable to explain the changes of the measured ele ctrical properties, of the detectors under irradiation. (C) 1999 Elsevier S cience B.V. All rights reserved.