  We report operation and characterization of a lab-assembled single-photon
detector based on commercial silicon avalanche photodiodes (PerkinElmer
C30902SH, C30921SH). Dark count rate as low as 5 Hz was achieved by cooling the
photodiodes down to -80 C. While afterpulsing increased as the photodiode
temperature was decreased, total afterpulse probability did not become
significant due to detector's relatively long deadtime in a passively-quenched
scheme. We measured photon detection efficiency higher than 50% at 806 nm.
