Effects of Gamma and Heavy Ion Damage on the Impulse Response and Pulsed Gain of a Low Breakdown Voltage Si Avalanche Photodiode

Effects of displacement and ionization damage on the impulse response of a high-bandwidth low breakdown voltage Si Avalanche Photodiode was investigated using a picosecond laser system. Damage was generated using either Co⁶⁰ gamma-irradiation or by scanning the device with an MeV ion microbeam. No shift in the impulse response characteristics and gain was observed for gamma doses as high as 100 kGy(Si). However, dark current measurements for irradiations with biases close to typical operating levels, exhibited enhanced ionization damage orders of magnitude higher than for no bias. Displacement damage introduced by the microbeam was used to differentiate between ionization damage in the guard ring isolation oxide and bulk damage. The absence of any marked change in the impulse response is discussed, as are possible mechanisms for the enhanced ionization damage