The avalanche delay effect in sine-gated single-photon detector based on InGaAs/InP SPADs

A sine-gated single-photon detector (SPD) intended for use in a quantum key distribution (QKD) system is considered in this paper. An "avalanche delay" effect in the sine-gated SPD is revealed. This effect consists in the appearance of an avalanche triggered at the next gate after the photon arrival gate. It has been determined experimentally that the nature of this effect is not related to the known effects of afterpulsing or charge persistence. This effect negatively affects the overall error rate in the QKD system. The influence of the main detector control parameters, such as temperature, gate amplitude and comparator's threshold voltage, on the avalanche delay effect was experimentally established

Investigation of the Effects of the Multiplication Area Shape on the Operational Parameters of InGaAs/InAlAs SPADs

A 2D model of an InGaAs/InAlAs single photon avalanche photodiode has been developed. The influence of the active area structure in the multiplication region on the diode's operating parameters has been studied. It was found that changing the diameter of the structure's active region leads to a change in the dark current in the linear part of the current-voltage curve and a change in the breakdown voltage. Reducing the diameter of the active region from 25 $\mu$m to 10 $\mu$m allowed decreasing the dark current in the linear mode by about $10$ dB. It has been shown that the quality of the SPAD device can be assessed by knowing the avalanche breakdown voltage and the overall current-voltage curve plot if we consider structures with the same multiplication region thickness and different remaining layers. The higher the breakdown voltage, the better the structure's quality due to smaller local increases in the field strength. Following this statement, we conclude that for further use in single-photon detectors, it is reasonable to pick specific SPADs from a batch on the sole basis of their current-voltage curves

Automated verification of countermeasure against detector-control attack in quantum key distribution

Attacks that control single-photon detectors in quantum key distribution using tailored bright illumination are capable of eavesdropping the secret key. Here we report an automated testbench that checks the detector's vulnerabilities against these attacks. We illustrate its performance by testing a free-running detector that includes a rudimentary countermeasure measuring an average photocurrent. While our testbench automatically finds the detector to be controllable in a continuous-blinding regime, the countermeasure registers photocurrent significantly exceeding that in a quantum regime, thus revealing the attack. We then perform manually a pulsed blinding attack, which controls the detector intermittently. This attack is missed by the countermeasure in a wide range of blinding pulse durations and powers, still allowing to eavesdrop the key. We make recommendations for improvement of both the testbench and countermeasure.Comment: 11 pages, 11 figures. Revised after referee reports from EPJ Quantum Techno

Dead time duration and active reset influence on the afterpulse probability of InGaAs/InP SPAD based SPDs

We perform the detailed study of the afterpulse probability's dependence in the InGaAs/InP sine-gated SPAD on the dead time and the used approach for its implementation. We have found that the comparator's simple latching can significantly reduce afterpulses' probability, even without using a dead time pulse that lowers the diode bias voltage. We have found that with a low probability of afterpulse ( 10 mus), it is sufficient to use a circuit with latching of the comparator, which will significantly simplify the development of an SPD device for applications in which such parameters are acceptable. We also proposed a precise method for measuring and the afterpulse and presented a model describing the recurrent nature of this effect. We have shown that it should not use a simple model to describe the afterpulse probability due to rough underlying physical processes. A second-order model is preferable