The fast development of mid-wave infrared photonics has increased the demand for high-performance photodetectors that operate in this spectral range. However, the signal-to-noise ratio, regarded as a primary figure of merit for mid-wave infrared detection, is strongly limited by the high dark current in narrow-bandgap materials. Therefore, conventional mid-wave infrared photodetectors such as HgCdTe require cryogenic temperatures to avoid excessively high dark current. To address this challenge, we report an avalanche photodiode design using photon-trapping structures to enhance the quantum efficiency and minimize the absorber thickness to suppress the dark current. The device exhibits high quantum efficiency and dark current density that is nearly three orders of magnitude lower than that of the state-of-the-art HgCdTe avalanche photodiodes and nearly two orders lower than that of previously reported AlInAsSb avalanche photodiodes that operate at 2 µm. Additionally, the bandwidth of these avalanche photodiodes reaches ~7 GHz, and the gain–bandwidth product is over 200 GHz; both are more than four times those of previously reported 2 µm avalanche photodiodes.

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Mid-wavelength infrared detection is useful for a variety of scientific and military applications. Avalanche photodiodes can provide an advantage for detection as their internal gain mechanism can increase the system signal-to-noise ratio of a receiver. We demonstrate a separate absorption, charge, and multiplication avalanche photodiode using a digitally-grown narrow-bandgap Al0.05InAsSb absorber for MWIR detection and a wide bandgap Al0.7InAsSb multiplier for low-excess-noise amplification. Under 2-μm illumination at 100 K the device can reach gains over 850. The excess noise factor of the device scales with a low k-factor of ~0.04. The unity-gain external quantum efficiency of the device peaks at 54% (1.02 A/W) at 2.35 μm and maintains an efficiency of 24% (0.58 A/W) at 3 μm before cutting off at ~3.5 μm. At a gain of 850 the device has a gain-normalized dark current density of 0.05 mA/cm2. This device achieves gains more than double state-of-the-art InAs detectors and gain-normalized dark current densities over two orders of magnitude lower than a previously reported MWIR Al0.15InAsSb-based detector.

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