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

Unexpected results have been obtained in measurements of dark-count rate an d 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 bath a low dark-count r ate and a QE of the order of 1%, which is at least one order of magnitude h igher than the values reported for such a device. The data offer hope for f uture diodes that might match such performance. Reasons for the device's ex traordinarily good performance, a performance level not matched by the othe r 17 APDs id the collection investigated, are not understood. Such high qua ntum efficiency germanium devices could be used in one-bit-per-photon commu nication systems operating in the 1540-nm telecommunications window.