Temperature Dependence Study of Dark Count Rate for Single Photon Detector High Voltage Bias Power Supply
Single photon detectors represent the ultimate sensitivity limit for optical measurements, capable of registering individual photons with high efficiency and temporal precision. These detectors find essential applications in quantum optics, quantum cryptography, light detection and ranging systems, and fundamental physics experiments where the signal levels approach the single photon regime. The dark count rate, representing spurious detection events in the absence of incident photons, fundamentally limits the detector sensitivity and the signal to noise ratio achievable in weak light measurements. This dark count rate exhibits significant temperature dependence, with the high voltage bias power supply playing a central role in determining the operating conditions that affect this critical performance parameter.
Single photon avalanche diodes operate in Geiger mode, biased above the breakdown voltage so that a single photon triggered carrier can initiate a self sustaining avalanche. The avalanche is quenched by external circuitry or the diode internal resistance, resetting the detector for subsequent events. The detection efficiency depends on the overbias, the amount by which the applied voltage exceeds the breakdown voltage, with higher overbias providing better photon detection probability but also increasing the dark count rate.
Dark counts arise from carriers that initiate avalanches through mechanisms other than photon absorption. Thermal generation of electron hole pairs in the depletion region provides a steady source of carriers that can trigger avalanches. Trap assisted generation through mid gap states contributes additional carriers, with the trap density and characteristics affecting the generation rate. Band to band tunneling at high electric fields can also generate carriers, becoming significant at high overbias levels. Each of these mechanisms exhibits characteristic temperature dependence that collectively determines the dark count rate temperature behavior.
Thermal carrier generation follows an exponential temperature dependence described by the Shockley Read Hall statistics. The generation rate increases with temperature as the thermal energy enables more carriers to overcome the band gap energy barrier. This exponential increase means that the dark count rate can change by orders of magnitude over practical temperature ranges, making temperature control critical for stable detector operation. The activation energy for thermal generation is approximately half the band gap for intrinsic generation, while trap assisted generation may have different activation energies depending on the trap energy levels.
The breakdown voltage of avalanche photodiodes also exhibits temperature dependence, typically increasing with temperature for silicon devices. This positive temperature coefficient means that a fixed applied voltage results in varying overbias as temperature changes. At higher temperatures, the increased breakdown voltage reduces the overbias for a fixed supply voltage, partially compensating the increased thermal generation rate. However, the temperature coefficient of breakdown voltage is typically insufficient to fully compensate the exponential increase in thermal generation, so the dark count rate still increases with temperature despite the reduced overbias.
The high voltage bias power supply can implement temperature compensation strategies to maintain more constant dark count rate over temperature variations. By measuring the detector temperature and adjusting the bias voltage accordingly, the overbias can be maintained at a constant value despite the temperature dependent breakdown voltage shift. Alternatively, the bias can be adjusted to maintain constant dark count rate, though this approach requires characterization of the dark count temperature dependence and may sacrifice detection efficiency at some temperatures.
Active cooling of single photon detectors dramatically reduces the dark count rate by suppressing thermal carrier generation. Thermoelectric coolers provide convenient cooling for many applications, achieving temperature reductions of tens of degrees below ambient. Cryogenic cooling using liquid nitrogen or closed cycle refrigerators enables even lower temperatures and correspondingly lower dark counts, essential for the most demanding applications. The high voltage supply must operate reliably at the cooled temperature and may need to accommodate the temperature dependent breakdown voltage shift.
Afterpulsing represents another temperature sensitive phenomenon in single photon detectors. Carriers trapped during an avalanche can be released after the quenching, triggering subsequent avalanches that appear as correlated dark counts. The trap release rates are temperature dependent, with higher temperatures enabling faster release and shorter afterpulse correlation times. However, the total afterpulse probability may be relatively temperature independent if the trap filling probability does not change significantly with temperature. The afterpulse characteristics affect the dead time and recovery behavior of the detector in addition to contributing to the effective dark count rate.
The high voltage power supply stability affects the dark count rate through variations in the overbias. Voltage ripple or noise modulates the overbias, causing corresponding variations in the avalanche triggering probability for both photon and dark carriers. The frequency spectrum of the voltage noise relative to the detector timing characteristics determines how the noise affects the measured dark count rate. Low frequency noise may cause slow drifts in the dark count rate, while high frequency noise may be averaged over many detection cycles.
Characterization of the dark count temperature dependence requires controlled temperature environments and precise measurement of both temperature and count rate. Temperature chambers or stages with integrated temperature sensors provide the controlled environment, while photon counting electronics measure the dark count rate. The characterization should cover the full operating temperature range and include multiple devices to capture device to device variation. The resulting temperature dependence data guides the selection of operating temperature and the design of any temperature compensation strategies.
Practical deployment of single photon detectors must consider the thermal environment and its impact on dark count performance. Ambient temperature variations in field applications may require active temperature stabilization or compensation. Heat dissipation from the detector and associated electronics can raise the local temperature above ambient, requiring thermal design to maintain acceptable operating temperatures. The integration of temperature sensing with the high voltage control enables implementation of temperature aware bias adjustment for optimal performance across varying conditions.
