Avalanche photodiodes optimized for Geiger-mode single photon counting at 1.06 microns have been fabricated using a quaternary InGaAsP absorber to reduce the dark count rate without sacrificing high photon detection probability. The dark count rate at a given detection probability is more than an order of magnitude lower than that of comparable Geiger-mode APDs fabricated with ternary InGaAs absorbers. Some devices show anomalous afterpulsing behavior that is reduced in severity at lower temperatures, the inverse of typical behavior. This unusual afterpulsing behavior allows for lower temperature operation without sacrificing maximum count rate, and may also offer new clues to the physical origin of afterpulsing in general.
We report on a 640 x 512 pixel, 25 μm pitch, InGaAs focal plane array based camera with the ability to perform range-gated imaging, while also allowing integration times longer than 32 ms for imaging in a staring mode at video rates. The combination of gated and video imaging is achieved through a high bandwidth pixel with a capacitive transimpedance amplifier (CTIA) design. The CTIA pixel may be switched between two feedback capacitor sizes to allow two different sensitivities and capacities, depending on the illumination conditions. Anti-blooming is included in the pixel to prevent charge spreading from oversaturated pixels. All pixels are gated simultaneously for "snapshot" exposure. The all solid-state gated camera is very reliable, in addition to being small and lightweight. The low dark current and high bandwidth of the InGaAs photodetectors enables both high sensitivity imaging at long exposure times and high bandwidth at short exposure times. The spectral response of InGaAs extends from 0.9 μm to 1.7 μm, allowing the use of eye-safe commercially available pulsed lasers with 1.5 μm wavelength, several millijoule pulse energies, and nanosecond scale pulse durations.
The single-photon detection efficiency of various commercial InGaAs/InP avalanche photodiodes (APDs) operated in the Geiger mode has been reported previously. These studies showed substantial photon detection efficiency variation between individual devices, but did not indicate what device parameters might be responsible for this variation. We present data on the external single-photon detection efficiency of APDs operated as near-infrared single photon counters, and show how detection efficiency is related to both device design and operating conditions. We have fabricated APDs with near-infrared single-photon detection efficiency exceeding 50% at 10% excess bias, demonstrating that InGaAs/InP APDs of the proper design are well suited to many practical applications of photon counting in the 1.0 to 1.7 micron wavelength band.