Performance evaluation of new large-area avalanche photodiodes for scintillation spectroscopy

Avalanche photodiodes (APDs) appear promising for certain applications as a solid state replacement for the photomultiplier tube. The increase in leakage current and capacitance noise with device active area has in the past kept the size of commercially available devices to < 1 mm2. Recent advances in fabrication technology have, however, resulted in relatively low-noise devices of up to 1 in. in diameter. We have recently evaluated the performance as scintillation spectroscopy detectors of two commercial large-area avalanche photodiodes. These APDs exhibit exceptional performance: at 662 keV a 1-in. diameter device coupled to a CsI(Tl) scintillator and operating at room temperature yielded 6.9% resolution and a 1-cm device coupled to CsI(Tl) and cooled to 260 K gave 4.4% resolution, which is believed to be the best resolution ever recorded for a scintillation spectrometer.