InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.
InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.
The implementation and commercialization of quantum cryptography technologies have to face some challenges related to the development of single-photon detectors operating at 1550 nm. The main requirements are: i) high detection efficiency; ii) low noise; iii) high count rate; iv) low timing jitter. Different technologies are currently available for single-photon detection at 1550 nm, but semiconductor devices (like Single-Photon Avalanche Diode, SPAD) offer a photon detection efficiency that is inherently higher than any photocathode employed in vacuum tube detectors. Additionally InGaAs/InP SPADs can detect single photons at 1550 nm with low noise when moderately cooled by means of thermo-electric coolers. Consequently, InGaAs/InP SPAD can be the enabling technology of practical quantum key distribution (QKD) systems, provided that the maximum count rate is increased above 1 Mcps. The main limit is the afterpulsing effect that usually sets too long (< 10 μs) a hold-off time after each avalanche ignition. We present the developments achieved in InGaAs/InP SPAD device design, fabrication technology and front-end electronics, aimed at decreasing the afterpulsing effect, while not impairing photon detection efficiency and timing jitter. The new InGaAs/InP SPADs provide count rates higher than 1 Mcps and temporal response with 60 ps Full-Width at Half Maximum and very short (30 ps time constant) tail. The front-end electronics includes a wide-band pulse generator able to gate the SPAD up to 133 MHz repetition rate. Eventually, a fast avalanche-quenching scheme minimizes quenching time to less than 1 ns, thus effectively reducing afterpulsing by decreasing the total charge flowing through the junction.
Experimental results obtained with silicon single photon avalanche diodes (SPADs) in quantum key distribution (QKD) at short wavelengths reveal remarkable potential for application in local area networks (LAN) and for free-space transmission at high rate. Actual application prospects, however, depend on the performance level and on the suitability of practical systems using the available silicon SPAD devices. They can be essentially divided in two groups: planar p-n junction structures with a thin depletion layer (typically 1 μm); and reach-through structures with a thick depletion layer (from 20 μm to 150μm). The physical mechanisms that control the device behaviour were investigated and the effect on the key parameters of the detector (quantum detection efficiency, dark counting rate, afterpulsing probability and photon-timing jitter) were thoroughly assessed. A quantitative analysis was made of the influence of such parameters on the quantum bit error rate (QBER). Actual parameters were measured and the attainable performance and system suitability of the two device types evaluated. Comparable performance is obtained, but from a system viewpoint thin SPADs appear inherently better suited to high-rate QKD applications, because of their faster response time, ruggedness, low voltage, low power dissipation and fabrication technology, which is simple, efficient, economical and compatible with monolithic integration of detector and associated circuits.
InGaAs/InP Single-Photon Avalanche Diodes (SPADs) are widely employed in quantum optics applications, particularly in Quantum Key Distribution (QKD), due to their high sensitivity in the near-infrared range. In QKD, low noise and high timing resolution are essential to ensure secure and high-rate key exchange. One of the main limitations of InGaAs/InP SPADs is afterpulsing, which degrades the quantum bit error rate (QBER), limits the maximum count rate, and can compromise both the security and throughput of QKD systems. Reducing afterpulsing is thus crucial for enabling high-speed, reliable quantum communication. We present a newly developed gating and quenching circuit that significantly reduces afterpulsing. The circuit is located entirely outside the detector package, maintaining compatibility with any InGaAs/InP SPAD, and supports both gated and free-running operation. Unlike integrated ASIC-based solutions, which offer low parasitics but are often limited by process constraints (e.g., low maximum voltages), our approach uses high-speed discrete components, allowing high excess bias operation and design flexibility. While discrete designs are typically more prone to parasitics, our compact layout effectively mitigates these effects and preserves signal integrity. Experimental results show a strong afterpulsing reduction compared to our current commercial module. Additionally, the measured SPAD current highlights that the avalanche is completely quenched in less than a nanosecond after sensing. Eventually, the small footprint of the design paves the way for a new generation of compact, low-afterpulsing InGaAs/InP SPAD modules suitable for high-performance quantum optics applications.
Free-running single photon detectors at telecom wavelengths are attractive for many tasks in quantum optics. However, until recently, the convenient and compact InGaAs/InP avalanche photodiodes did not operate with satisfactory performance in this regime due to high dark count rates and afterpulsing effects. Recent development of negative feedback avalanche diodes (NFADs) enabled very fast passive quenching of the avalanche current, effectively reducing the afterpulse probability and subsequently allowing free-running operation. Here, we present analysis of NFAD operation at low temperatures, down to 163 K, which reveals a significant reduction of the dark count rate. We succeeded in developing a compact single photon detection system with a dark count rate of ~1 cps at 10% detection efficiency. To ensure that the NFAD is in a well-defined initial condition during the characterization of the detection efficiency and afterpulsing, we use a recently developed FPGA based test procedure suitable for free-running detectors. To demonstrate the performance of the detector in a real-world application we integrate it into a 1.25 GHz clocked quantum key distribution system. An optimization of the detector temperature allowed secret key distribution in the presence of more than 30 dB of loss in the quantum channel.
The application of quantum key distribution (QKD) has raised particular demands for single-photon detectors. One of the most promising candidates at the low-loss optical fibre communications windows is the planar geometry InGaAs/InP single-photon avalanche diode. These detectors have been modelled, fabricated and characterised at 1.55 µm wavelength. Their performance in terms of single-photon detection efficiency, dark count rate, timing jitter and afterpulsing behaviour are reported and compared with the best commercially available, linear multiplication avalanche photodiodes operated in Geiger-mode. Their use in the application of QKD is discussed.
Single-photon detection concept is the most crucial factor that determines the performance of quantum key distribution (QKD) systems. In this paper, a simulator with time domain visualizers and configurable parameters using continuous time simulation approach is presented for modeling and investigating the performance of single-photon detectors operating in Gieger mode at the wavelength of 830 nm. The widely used C30921S silicon avalanche photodiode was modeled in terms of avalanche pulse, the effect of experiment conditions such as excess voltage, temperature and average photon number on the photon detection efficiency, dark count rate and afterpulse probability. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result emerged from the simulated data generated and detected by commercial devices is that the modeling process provides guidance for single-photon detectors design and characterization. The validation and testing results of the single-photon avalanche detectors (SPAD) simulator showed acceptable results with the theoretical and experimental results reported in related references and the device's data sheets.