STUDY OF RESISTIVITY AND MAJORITY CARRIER CONCENTRATION OF SILICON DETECTORS DAMAGED BY NEUTRON-IRRADIATION UP TO 10(16) N CM(2)/

Working characteristics of silicon radiation detectors have been obser ved to change, when irradiated at very large neutron fluences (Phi > 1 0(12) n/cm(2)), due to the generation of defect levels and capture of majority carriers on these levels. Direct study and confirmation of th ese phenomena were made by measuring the Hall effect constant R-H and resistivity of the silicon material as a function of neutron irradiati on of up to about 9 x 10(15) n/cm(2). It was found that, for fluences of Phi greater than or equal to 5.95 x 10(14) n/cm(2), the sign of the Hall constant R-H changes from negative to positive. Taking into acco unt that, for Phi greater than or equal to 1.19 x 10(14) n/cm(2), the value of resistivity rho is independent of the fluence, we assumed tha t the damage caused by those neutron fluences was high enough to creat e disordered silicon crystal structures, This disordered silicon may c ontribute to the positive sign of R-H and make the rho of this materia l insensitive to further neutron irradiation. This can be explained by assuming that, for Phi > 1.19 x 10(14) n/cm(2), the created disordere d silicon material has an equivalent resistance in series with the sin gle crystal Si resistance. The contribution to rho of the disordered s ilicon is large enough to have a strong influence on the silicon chara cteristics. The new defect structure was seen under a microscope on et ched samples, irradiated at Phi > 10(13) n/cm(2).