The Effect of Nuclear Radiation on Selected Semiconductor Devices

Selected samples of both germanium and silicon devices have been exposed to a nuclear radiation environment. This environment consisted of either a fission-produced gamma spectrum or a combined neutron and gamma spectrum as obtained in the graphite region of the Materials Testing Reactor in Scoville, Idaho. Several parameters of the devices were measured before, during, and after irradiation. Noise and photovoltaic voltages were observed during exposure to a gamma flux of 2×106 Roentgens/ hour (R/hr). In some devices, transient changes occurred in those parameters sensitive to surface conditions. After continued exposure of from 5×105 to 5×108 Roentgens or 5×1010 to 5×1013 neutrons per square cm, permanent damage occurred in the device characteristics. No real distinction could be made between silicon or germanium devices so far as noise, photovoltaic, or transient effects are concerned. However, there is a marked difference between silicon and germanium devices with respect to permanent damage. Silicon devices are more susceptible to damage in parameters dependent upon the minority carrier lifetime such as the current gain, the forward resistance of high efficiency diodes, and the valley voltage of unijunction transistors. Germanium devices are also susceptible to the conversion of n material to p type and this results in the reduction of the punch-through voltage of p-n-p germanium transistors. For both silicon and germanium transistors it was found that the thinner base transistors were the more resistant to reduction in current gain.