Avalanche photodiode (APD) is a photodetector that converts incident photon into photocurrent with high efficiency and simultaneously has multiplication function caused by impact ionization. The quantum efficiency of the photomultiplier tube (PMT) is about 20 % in visible and near-infrared region, while the efficiency of the silicon APD is higher than 80 %. Therefore, APD is widely used in high energy experiments and medical imaging as well as in optical communication. In this study, the absolute quantum efficiencies of a photodiode (PD) as well as an APD were measured. Using a preamplifier capacitor and calibrated photodiode, the ratio of ADC channel to charge was measured as (1.20 ± 0.14) ADC/fC, which was used as an absolute parameter to calculate the quantum efficiency. The LED light of blue (450 nm), green (570 nm) and red (650 nm) was irradiated to the calibrated PD and each detector using the integrating sphere and the power of the LED light and the ADC channel were measured simultaneously. The gain, which is the main characteristics of the APD, was measured by two methods: one uses the electrical characteristics of the APD and the other compares the ADC channel. The measured gain was compared with the gain provided by the manufacturer. Utilizing these gain results, the absolute quantum efficiencies of the APD and PD were measured as well.
Thesis Advisor: Prof. Hongjoo Kim