Development of a Semiconducior Neutron Dosimeter with a PIN Diode

Abstract

When a Si PIN diode is exposed to fast neutrons,it produces displacement in Si lat1ice structure of the diode. Defects induced from structural dislocation become effective recombination centers for carriers which pass through the base of a PIN diode. Hence, increasing the resistivity of the diode decreases the current for the applied forward vo1tage. This paper involves the development of a neutron sensor based on the phenomena of the displacement effect damaged by neutron exposure. The neutron efl:i?cton the serniconductor was analyzed,a nd multi PIN diode arrays with various intrinsic layer(Ilayer)thicknesses and cross sections were fabricated. Under irradation tests with a neutron beam,the manufactured diodes have good characteristics of linearity in an eutron irradiation experiment and give results that the increase of thickness of 1 layer and the decrease of the cross-section of the PIN diodes improve the sensitivity. Newly developed PIN diodes with a?rickerI layer and various cross sections were retested and showed the best neutron sensitivity in the condition that the 1 layer thickness was sirnilar to the length of as ide of the cross-section. On the basis of two test results,f inal PIN diodes with a rectangular shape wer?manufacturedand the characteristics for neutron detectors were?alyzed through the neutron beam test using the on-line electronic dosimetry system. The developed PIN diode shows a good linearity to absorbed dose in the range of 0 to 1,000cGy (Tissue) and its neutron sensitivity is 13mV/cGy at a constant current of 5MA., that is three times higher than that of silmilar commercially developed neutron detectors. Moreover the device shows less dependency on the orientation of the neutron beam and a considerable stability in an annealing test for a long period.