Photon counting in the 1540-nm wavelength region with a germanium avalanche photodiode

Unexpected results have been obtained in measurements of dark-count rate and quantum efficiency (QE) for a germanium avalanche photodiode operating in the photon counting regime at 1540-nm wavelength. A liquid-nitrogen cooled Ge single-photon avalanche diode (SPAD) exhibited both a low dark-count rate and a QE of the order of 1%, which is at least one order of magnitude higher than the values reported for such a device. The data offer hope for future diodes that might match such performance. Reasons for the device's extraordinarily good performance, a performance level not matched by the other 17 APDs in the collection investigated, are not understood. Such high quantum efficiency germanium devices could be used in one-bit-per-photon communication systems operating in the 1540-nm telecommunications window.