Study of silicon photodiode performance for X-ray detector in cargo system

In this study, we manufactured silicon PIN photodiodes coupled with a scintillator for X-ray detection in cargo inspections. The classification of photodiodes is made based on their depletion characteristics into two categories: fully depleted (FD) sensor and non-fully depleted (NFD) sensor. We manufactured the photodiodes on an n-type silicon wafer of diameter 6-in., a high resistivity (>5kΩcm) and low resistivity (>100Ωcm) for the FD and NFD sensors, respectively. The light entrance windows for the scintillation light were designed on the ohmic and junction sides of the FD and NFD sensors, respectively. Since the NFD sensor is not fully depleted, it can be operated at a lower bias voltage, and therefore has a lower leakage current. We measured the electrical characteristics, quantum efficiencies, and energy resolutions of the fabricated FD and NFD photodiodes coupled with or without a CsI(Tl) crystal using alpha particles from a ²⁴¹Am radioactive source. We present results of the comparison between the FD and NFD sensors.