The capability to achieve high count rates has become an imperative in the most areas where near-infrared single-photon counters are required to detect photons up to 1.7 μm. Hence, afterpulsing mitigation is a dominant theme in recent works concerning systems based on InGaAs/InP SPADs. Given the challenges inherent in reducing the density of defects that give rise to the carrier trapping events causing afterpulsing, the only viable approach is to reduce the potential number of carriers that can be trapped by limiting the charge flow per avalanche event. In this paper we present a sine-wave gating system based on the balanced detector configuration. The gate frequency is programmable in a wide range (1.0 – 1.6 GHz) for allowing synchronization with an external laser system and for exploring the best trade-off between afterpulsing and photon detection efficiency. The long-term stability can be achieved with a stable cancelation of the gate feedthrough. In this work this is guaranteed by a feedback loop that continuously monitors the residual output power at the gate frequency and adjusts the amplitude and phase of the two sinusoids fed to the SPAD-dummy couple.
CMOS SPADs are nowadays an established imaging technology for applications requiring single-photon sensitivity in a compact form-factor (e.g. three-dimensional LIDAR imaging and fluorescence lifetime FLIM microscopy). However, we aimed at further enhance overall SPAD performances, by exploiting smart power technologies, such as the BCD (Bipolar-CMOS-DMOS) one. We achieved the present state-of-the-art SPADs fabricated in the 0.16 μm BCD technology by STMicroelectronics, attaining >60% photon detection efficiency at 500 nm, dark count rate density < 0.2 cps/μm<sup>2</sup>, and less than 30 ps FWHM timing jitter.
We present a new InGaAs/InP Single-Photon Avalanche Diode (SPAD) with high detection efficiency and low noise,
which has been employed in a sinusoidal-gated setup to achieve very low afterpulsing probability and high count rate.
The new InGaAs/InP SPAD has lower noise compared to previous generations thanks to the improvement of Zinc
diffusion conditions and the optimization of the vertical structure. A detector with 25 μm active-area diameter, operated
in gated-mode with ON time of tens of nanoseconds, has a dark count rate of few kilo-counts per second at 225 K and
5 V of excess bias, 30% photon detection efficiency at 1550 nm and a timing jitter of less than 90 ps (FWHM) at 7 V of
In order to reduce significantly the afterpulsing probability, these detectors were operated with a sinusoidal gate at 1.3
GHz. The extremely short gate ON time (less than 200 ps) reduces the charge flowing through the junction, thus
reducing the number of trapped carriers and, eventually, lowering the afterpulsing probability. The resulting detection
system achieves a maximum count rate higher than 650 Mcount/s with an afterpulsing probability of about 1.5%, a
photon detection efficiency greater than 30% at 1550 nm and a temporal resolution of less than 90 ps (FWHM).