Photo-Responses of Silicon Photodiodes with Different ARC Thicknesses for Scintillators

We designed and fabricated silicon positive-intrinsic-negative (PIN) photodiodes coupled with a scintillator for radiation detection. The photodiodes were fabricated on an n-type double-sided polished silicon wafer with a diameter of 6-in., a high resistivity (<5kΩ·cm), and a <100> orientation. To increase the quantum efficiency (QE) of the photodiode, an anti-reflection coating (ARC) was provided on the side where light entered. It is difficult to realize an ARC with an uniform thickness in the sensor fabrication process. The effect of changes in the ARC thickness on the QE of the fabricated sensors was studied in detail. We measured the electrical characteristics and compared their quantum efficiencies as a function of the incident light wavelength for the photodiodes with different ARC thicknesses. In this paper, we present the design of the photodiodes and their measured electrical characteristics and photo-responses for different ARC thicknesses. From measurements of the wavelength-dependent QE, we determined the refractive index of the ARC layer to be 2.25 ± 0.15. The ARC layer improved the QE up to 56% and 63% at the wavelengths of 550 and 475 nm, which correspond to the wavelengths of the scintillation light from CsI(Tl) and CdWO₄, respectively.