Optimizing photodetectors for radiation environments

An analysis is presented of the analog signal response of Si and other photodiode materials to light and to ionizing radiation for single-pass, two-pass, and multipass optical detectors. The analog signal analysis represents a worst case calculation so that photodiodes in digital data links will exhibit higher radiation tolerances. Maximum allowable radiation dose rates are determined as a function of the effective collection depth which is defined as the width of the collection region for minority carriers. The calculations indicate that proper selection of detector material will permit signal detection in the presence of dose rates as high as 2 times 10 to the 6 rads/sec per mW/sq cm of light power in a realistic photodiode structure. The analytic parameters used in the calculations for Si are verified experimentally.