A low-noise avalanche photodiode (APD) for 2-μm detection, developed by engineers at the University of Virginia (UVA) and the University of Texas-Austin (UT-Austin), could provide high-power, eye-safe light imaging, detection, and ranging for lidar applications. According to the team, the new APD has demonstrated record performance. To build the APD, engineers at UT-Austin used molecular beam epitaxy to grow a digital alloy composed of aluminum, indium, arsenic, and antimony. The alloy combines long-wavelength sensitivity, ultralow noise, and the design flexibility that is needed to achieve low dark currents, a capability that is not available with existing low-noise APD materials technologies, the researchers said. “Our ability to control the crystal growth process down to the single atom-scale enables us to synthesize crystals that are forbidden in nature, as well as design them to simultaneously possess the ideal combination of fundamental material properties necessary for efficient photodetection,” UT-Austin professor Seth R. Bank said. Epitaxial cross section of the avalanche photodiode design. Doping concentrations are given in cm−3. Courtesy of Joe C. Campbell. The APD could be used for compact, high-sensitivity lidar receivers in applications that require high-resolution sensors that can detect greatly attenuated optical signals reflected from distant objects, such as robotics, autonomous vehicles, wide-area surveillance, and terrain mapping. Eye safety has limited the adoption of these next-generation lidar systems, because the requisite higher laser power poses an increased risk of eye damage, the researchers said. “The 2-μm window is ideal for lidar systems because it is considered eye-safe and extends the detection reach,” UVA professor Joe C. Campbell said. “I can envision our avalanche photodiode impacting numerous key technologies that benefit from high-sensitivity detectors.” The work on the new APD is being transferred to IQE for foundry services and Lockheed Martin to develop photodiode arrays with readout circuitry. Future work at the two universities will concentrate on achieving low-noise operation at near-room temperatures, extending the operating wavelengths further into the infrared, and pushing the sensitivity to the single photon level. The research was published in Nature Photonics (www.doi.org/10.1038/s41566-020-0637-6).