Protocols for healing radiation damaged single-photon detectors suitable
for space environment
Abstract
Single-photon avalanche detectors (SPADs) are well-suited for
satellite-based quantum communication because of their advantageous
operating characteristics as well as their relatively straightforward
and robust integration into satellite payloads. However, space-borne
SPADs will encounter damage from space radiation, which usually
manifests itself in the form of elevated dark counts. Methods for
mitigating this radiation damage have been previously explored, such as
thermal and optical (laser) annealing. Here we investigate in a lab,
using a CubeSat payload, laser annealing protocols in terms of annealing
laser power and annealing duration, for their possible later use in
orbit. Four Si SPADs (Excelitas SLiK) irradiated to an equivalent of 10
years in low Earth orbit exhibit very high dark count rates
(>300 kcps at -22 C operating temperature) and significant
saturation effects. We show that annealing them with optical power
between 1 and 2 W yields reduction in dark count rate by a factor of up
to 48, as well as regaining SPAD sensitivity to a very faint optical
signal (on the order of single photon) and alleviation of saturation
effects. Our results suggest that an annealing duration as short as 10
seconds can reduce dark counts, which can be beneficial for
power-limited small-satellite quantum communication missions. Overall,
annealing power appears to be more critical than annealing duration and
number of annealing exposures.