Study of resistivity and majority carrier concentration of silicon damaged by neutron irradiation

Working characteristics of silicon radiation detectors have been observed to change, when irradiated at very large neutron fluences (phi>10(12) n/cm(2)), due to generation of defect levels and capture of majority carriers on these levels. Direct study and confirmation of these phenomena were made by measuring the Hall effect constant R-II and Resistivity, of the silicon material as a function of neutron irradiation of up to about 9 x 10(15) n/cm(2). It was found that, for fluences of about phi greater than or equal to 5.95x10(14) n/cm(2), the sign of the Hall constant R-H changes from negative to positive. Taking into account that, for phi greater than or equal to 1.19x10(14) n/cm(2), the value of rho is independent on fluence, we assumed that the damage, craused at those neutron fluences, was high enough to create disordered silicon crystal structures. ?his disordered silicon may contribute to the positive sign of R-II and make the rho of this material insensitive to further neutron irradiation. This can be explained by assuming that, for phi>1.19x10(14) n/cm(2), the created disordered silicon material has an equivalent resistance in series with the single crystal Si resistance. The contribution to rho of the disordered silicon is large enough to have a strong influence on the silicon characteristics. nle new defect structure was seen under a microscope on etched samples, irradiated at phi>10(13) n/cm(2).