Radiation Testing of PIN Photodiodes

PIN photodiodes representative of commercially available device types were radiation tested in total dose, neutron fluence, and ionization pulse environments to examine the vulnerability mechanisms that occur. Also included in the testing was a special epitaxial device that was designed to have a small ionization-sensitive volume. It was found that surface shunt paths were produced in all the devices, with the effects in the p-on-n devices with guard rings being particularly bad. These shunt paths produced a decreased optical response and an increased dark current. In devices biased to less than full depletion, lifetime degradation was observed. This caused significant optical response degradation, especially at longer wavelengths, and gave a significant contribution to the increased dark current. The epitaxial device had the predicted small ionizationsensitive volume, and no unusual vulnerability mechanism occurred in the device. In fact, it was generally at least as radiation-toleranct as any of the other devices, and thus is a good choice for use in applications requiring radiation hardness.