Counting, timing, and tracking with a single-photon germanium detector.
We report the performance of a germanium quad-cell, composed of four avalanche photodiodes operated in the photon-counting regime, biased above the breakdown voltage. Each pixel detects a single photon in the wavelength range 1-1.5 microm with ~10% quantum efficiency and measures the photon arrival time with a time resolution of 100 ps. By adopting a multiplexed gating of the avalanche photodiodes we avoided the optical cross talk among pixels, thus achieving a noise-equivalent power of 3 x 10(-15) W/Hz((1/2)) for each pixel and demonstrating the tracking capabilities of such a detector.
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