This paper describes single photon detection for Ge on Si separate-absorption-charge-multiplication (SACM) avalanche
photodiodes and advances in quenching for InP/InGaAs single photon avalanche diodes.
We report reduced afterpulsing for a high-performance InGaAs/InP single photon avalanche photodiode (SPAD) using a
gated-mode passive quenching with active reset (gated-PQAR) circuit. Photon detection efficiency (PDE) and dark count
probability (DCP) were measured at a gate repetition rate of 1 MHz. With a double-pulse measurement technique, the
afterpulsing probability was measured for various hold-off times. At 230K, 0.3% afterpulsing probability for a 10 ns
hold-off time was achieved with 13% PDE, 2×10<sup>-6</sup> DCP and 0.4 ns effective gate width. For the same hold off time,
30% PDE and 1×10<sup>-5</sup> DCP was achieved with 6% afterpulsing probability for an effective gate width of 0.7 ns.
We report an improved passive-quenching-with-active-reset (PQAR) circuit that can operate in a free-running mode with
reduced afterpulsing. A dynamic range of approximately 80 dB has been achieved. A model that reveals the factors that
determine the dynamic range is described. The PQAR circuit approach can also be utilized in gated mode, which we
refer to as gated-PQAR circuit. Compared to conventional gated quenching, the gated-PQAR circuit can significantly
reduce the current flow during avalanche. This will reduce afterpulsing and provide the capability of utilizing wider ac
bias pulses, which will ease restrictions on synchronization with the arrival of incident photons.
LAser Detection And Ranging (LADAR) is a promising tool for precise 3D-imaging, which enables field
surveillance and target identification under low-light-level conditions in many military applications. For the time
resolution and sensitivity requirements of LADAR applications, InGaAsP/InP Geiger-mode (GM) avalanche
photodiodes (APDs) excel in the spectrum band between 1.0~1.6 μm. Previously MIT Lincoln Laboratory has
demonstrated 3D LADAR imaging in the visible and near infrared (1.06 μm) wavelengths with InP/InGaAsP GM-APD
arrays. In order to relieve the design tradeoffs among dark count rate (DCR), photo detection efficiency (PDE),
afterpulsing, and operating temperature, it is essential to reduce the DCR while maintaining a high PDE. In this
paper we will report the progress of GM-APD detectors and arrays with low DCR and high PDE at 1.06 μm.
In order to improve both DCR and PDE, we optimized the multiplication layer thickness, substrate, and
epitaxial growth quality. With an optimized InP multiplier thickness, a DCR as low as 100 kHz has been
demonstrated at 4V overbias at 300 °C. and at 240 K, less than 1 kHz DCR is measured. A nearly 40% PDE can be
achieved at a DCR of 10 kHz at the reduced temperature.
In this paper, we report a new quenching circuit for single photon avalanche diodes, passive-quenching-with-activereset.
This circuit uses a large resistor to passively quench the avalanche current and a transistor to actively reset the
diode to the operating voltage after a specified hold-off time. Afterpulsing is reduced by minimizing the total charge
flow during avalanche, which can be achieved by minimizing the stray capacitance in the circuit. The simulation of the
circuit using PSpice showed that the circuit is operating correctly. The operation of the circuit was demonstrated using
discrete components. A quenching time of ~2ns and a dynamic range of ~100dB have been achieved. The performance
can be further improved by integrating the transistor with the photodiode to reduce the stray capacitance.