Consideration of the leakage-current and the radiation-response characteristics of silicon PIN detectors with different N-type substrates and their application to a personal gamma-ray dosimeter

Abstract

The effects of resistivity and crystal orientation on the leakage-current and the radiation-response characteristics of silicon PIN detectors have been studied. A high-resistive substrate (> 8 k Omega.cm) shows a larger leakage current than a low-resistive one (< 4 k Omega.cm) at low reverse bias because of its wider depletion width, but the opposite result is seen at high reverse bias. We think that the thermionic field emission (TFE) current increases at high reverse bias for a low-resistive substrate. The detector with a (111)-oriented substrate exhibits leakage current chacteristics comparable to those of the (100)-oriented one when the resistivity of the substrate is 3.8 k Omega.cm. An X-ray beam irradiation test showed that the output current of the detector with the (Ill)-oriented substrate was 20 % higher than that of the (100) -orientated one and that the result was independent of the resistivity of the substrate. Based on the results, we fabricated a silicon PIN detector for a personal gamma ray dosimeter operated at 3 V with a substrate having a (111) orientation and a resistivity of 3.8 k Omega.cm, and we assembled it with read-out integrated circuit. Our detector was sensitive to Cs-137 natural gamma rays and showed a good linearity in the exposure rate.