Afterpulsing in Ge-on-Si Single-Photon Avalanche Diodes

In this letter, we investigate afterpulsing in 26 and
$100~\mu \text{m}$
diameter planar geometry Ge-on-Si single-photon avalanche diode (SPAD) detectors, by use of the double detector gating method with a gate width of 50 ns. Ge-on-Si SPADs were found to exhibit a 1% afterpulsing probability at a delay time of
$200~\mu \text{s}$
and temperature of 78 K, and
$130~\mu \text{s}$
at a temperature of 150 K. These delay times were measured with an excess bias of 3.5% applied, which corresponded to a single-photon detection efficiency of 15% at
$1.31~\mu \text{m}$
. We demonstrate that reducing the detector diameter can also be an effective way to restrict afterpulsing in this material system.