Study of resistivity and majority carrier concentration of silicon detectors damaged by neutron irradiation up to 10 16 n/cm 2

Abstract

Working characteristics of silicon radiation detectors have been observed to change, when irradiated at very large neutron fluences ( Φ > 10 12n/cm 2), due to the 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 H and resistivity of the silicon material as a function of neutron irradiation of up to about 9 × 10 15 n/cm 2. It was found that, for fluences of Φ ≥ 5.95 × 10 14n/cm 2, the sign of the Hall constant R H changes from negative to positive. Taking into account that, for Φ ≥ 1.19 × 10 14n/cm 2, the value of resistivity ϱ is independent of the fluence, we assumed that the damage caused by those neutron fluences was high enough to create disordered silicon crystal structures. This disordered silicon may contribute to the positive sign of R H and make the ϱ of this material insensitive to further neutron irradiation. This can be explained by assuming that, for Φ > 1.19 × 10 14n/cm 2, the created disordered silicon material has an equivalent resistance in series with the single crystal Si resistance. The contribution to ϱ of the disordered silicon is large enough to have a strong influence on the silicon characteristics. The new defect structure was seen under a microscope on etched samples, irradiated at Φ > 10 13n/cm 2.