Candidate: Jin Gyu Lim
Title: Laser annealing of irradiated silicon single-photon avalanche photodiodes for quantum satellite receiver
Date: March 23, 2018
Time: 2:00 PM
Place: E5 4106-4128
Supervisor(s): Jennewein, Thomas (Quantum Computing) - Bajcsy, Michal
Abstract:
Single-photon avalanche photodiodes (SPADs) are a practical option for space-based quantum communications requiring single-photon detection. However, radiation damage to SPADs significantly increases their dark count rates and thus reduces their useful lifetimes in orbit.
I will first show that high-power laser annealing of irradiated SPADs of three different models (Excelitas C30902SH, Excelitas SLiK, and Laser Components SAP500S2) heals the radiation damage and several SPADs are restored to typical pre-radiation dark count rates. Of nine samples we test, six SPADs were thermally annealed in a previous experiment as another solution to mitigate the radiation damage. Laser annealing reduces the dark count rates further in all samples with the maximum dark count rate reduction factor varying between 5.3 and 758 when operating at 80C. This indicates that laser annealing is a more effective method than thermal annealing. The illumination power to reach these reduction factors ranges from 0.8 1.6 W. Other photon detection characteristics, such as photon detection efficiency, timing jitter, and afterpulsing probability, fluctuate but the overall performance of quantum communications should be largely unaffected by these variations. These results herald a promising method to extend the lifetime of a quantum satellite equipped with SPADs.
Next, I will present second round of laser annealing. This starts off with radiation simulation to determine radiation dosages for different lifetimes in space for radiation test per- formed on Laser Components SAP300s. After proton irradiation, the samples from each damage group are then laser-annealed using the same method in the first project (60s continuous exposure) and the results show that they all recover the dark count rate close to the pre-radiation values at 22 C. The optical power to achieve such reduction is from 800 1000 mW. In addition, new laser annealing methods are explored. 180 s continuous exposure and 50% duty cycle method for 60 s exposure could also return the dark count rate to pre-radiation levels when the average illumination power is from 800 1000 mW. These results imply that the thermal effect is the main contributor of laser annealing. However, I will also show that forward-bias current annealing on one sample can reduce the dark count rate at a much faster rate than any laser annealing methods. As a result, more tests need to be done to investigate the causes of the laser annealing effect further.