Observations in changes of electrical properties in thermally neutron-exposed boron-doped silicon semiconductors

Boron-doped resistors and transistors were developed using various levels of boron concentration. These were exposed to a thermal neutron flux of about 2 × 10⁸ s⁻¹ cm⁻² at various fluences, at Los Alamos National Laboratory. Characterization of some electrical properties was carried out before and after irradiation. The reaction, ¹⁰B þ n → Li þ α, and others, caused by neutron irradiation, introduced impurities in the silicon lattice, thus producing measurable differences in electronic parameters. The results show that for irradiated resistors possessing very low values of boron concentration (≈10¹⁴ cm⁻³), there is a significant reduction (i.e., orders of magnitude) in resistivity, for the higher fluences studied (2 × 10¹¹–10¹² cm⁻²). This trend is not seen for high values of boron concentration (≈10²¹ cm⁻³), nor for the low-boron-concentration specimens exposed to a lower fluence. These observations appear to be in accordance with the deep-trap level behavior, and, though requiring further study, they seem to be promising for the potential application on neutron radiation detection. Additionally, there was no observation of significant changes in other electronic parameters, such as threshold voltage or trans-conductance, for the transistors exposed and tested.