Stability of Photodiodes Under Irradiation With 157-nm Pulsed Excimer Laser
Ping-Shine Shaw, R Gupta, Keith R. Lykke
We have measured the stability of a variety of photodiodes as they are irradiated with UV light from a pulsed excimer laser source operating at 157 nm using a radiometry beamline at the Synchrotron Ultraviolet Radiation Facility (SURF III) at the National Institute of Standards and Technology (NIST). The intense, pulsed laser radiation exposed the photodiodes whereas the low intensity, continuously-tunable radiation from the synchrotron source characterized the photodiodes. The detectors studied include several silicon photodiodes with different passivating layers and several Schottky-barrier type photodetectors. We measured the degradation of the detector at 157 nm as a function of the total accumulated dose from the excimer laser as well as the absolute spectral responsivity and reflectance of these photodetectors before and after exposing the detector to the 157 nm radiation. The measurement results confirmed the important role of interface trap states generated by laser irradiation. A simple model based on the interface states generation was proposed to describe the change of detector responsivity as a function of the accumulated dose from laser irradiation. We also observed the slow recovery in detector responsivity of some of the photodiodes tested and detector degradation caused by low power continuous 157 nm radiation as compared to those caused by 157 nm laser pulses. For the most radiation-hard detectors tested, measurement results indicate that the deposition of a thin layer on top of the detectors during laser irradiation is responsible for the change in detector responsivity.