Electric Field Distortion in Electro-Optical Devices Subjected to Ionizing Radiation

摘要

Insulators exposed to the combined effects of an intense electric field and ionizing radiation frequently exhibit trapped-charge effects, the most notable example being the oxide in MOSFET devices. This report explores a heretofore neglected radiation damage mechanism in electrooptically tunable filters (EOTF) and other electro-optical devices requiring field strengths. This mechanism is the gross perturbation of the electric field as a result of trapped space charge. We set up the equations for calculating the changes in electric field under irradiation for two different models; (1) for blocking contacts with negligible trapping in the bulk, and (2) for ohmic contacts with bulk trapping. The results are expressed in terms of physical parameters, some of which are not known for AgGaS2, the material most likely to be used for the infrared EOTF. More experimental work is needed in order to make accurate predictions, but by estimating reasonable values for the unknown physical parameters, using Si02, as a guideline, we find that for either model a dose of about 100,000 rad is consistent with a field degradation of 50%. From the uncertainty in physical parameters, the effect described could equally well occur at both higher and lower dosages.