Photodetectors for X- and γ-Ray Scintillators

The article analyzes X- and γ-ray detectors based on the ionizing and scintillation principles of operation. The effectiveness of using silicon p-i-n and p-n photodiodes in scintillation sensors for detecting visible photoluminescent radiation is investigated. The p-i-n detector was fabricated on the basis of p-type single crystal silicon with orientation [111] and resistivity 8-10 kΩ∙cm. The p-n photodiode was fabricated on the basis of n-type single crystalline silicon with orientation [111] and resistivity 200-300 Ω∙cm. It was found that p-n photodiodes have a much lower dark current than p-i-n photodiodes (although somewhat inferior in sensitivity), which provides their advantage in detectivity. However, if it is necessary to register short pulses of luminescent radiation, p-i-n photodiodes should be used, since they have a higher response speed. The increase in response speed is due to the fact that the process of diffusion of charge carriers in a p-n structure of a photodiode is replaced in the p-i-n structure by the drift of charge carriers through the i-region in a strong electric field.