Electrical characteristics and radiation detection performance of large-area photodiodes

Photodiodes with the size of 2.3 x 2.3 cm(2) are fabricated on n-type silicon wafers with high resistivity (> 5 k Omega center dot cm) for physics applications. The photodiodes are fully depleted to collect signals produced by incoming particles. We measure the leakage currents and the capacitances of the photodiodes as functions of the reverse bias voltage. The photodiodes with leakage currents < 70 nA/cm(2) are used to measure the signal-to-noise ratio (SNR) by using a 45 MeV proton beam from the MC-50 cyclotron at the Korea Institute of Radiological and Medical Sciences (KIRAMS) and a Sr-90 radioactive source. The SNRs are measured for the photodiode only and for photodiode coupled with a 5 mm thick plastic scintillator. The proton beam energy is controlled by using a degrader, and the pulse heights are measured for different energies of the proton beam. The radiation damage effect is also measured in an environment of 1.18 x 10(10) protons/cm(2). In this paper, we present not only the SNR measurements using the proton beam and the radioactive source but also the result of the radiation damage test.