Effective neutron detecting threshold of silicon transistors under irradiation

Silicon bipolar, planar, planar-epitaxial and mesa-transistors are investigated for determining the effect of the transistor design and technology of its fabrication on the change of gain during neutron irradiation of different energy composition. Measuring the neutron spectra is carried out by means of a set of activation detectors. Average energies of neutron spectra make up 1.35-2.85 MeV. Time of irradiation has been chosen so, that the gain could change in 25-30%. The results obtained show that the transistors produced by mesa-technology sharply differ by nonlinearity of gain change depending on the neutron fluence and variation of radiation stability from one sample to another. The carried out results make it possible to determine the range of optimal thresholds of neutron detection, which provide the given variation, in the changes of the gain. So, at the given 20% variation the optimal threshold for all the investigated transistors and fast neutron spectra lies within the range from 0.27 to 0.87 MeV. It is concluded on the basis of the results obtained, that neutron fluence measured by a threshold detector on the neptunium-237 (0.65 MeV threshold) or rhodium-104 (0.8 MeV threshold) base can be used as an exposure unit during radiation tests of silicon semiconducting devices