Electronic engineers from the University of Virginia, working with colleagues from the University of Texas at Austin, have developed an avalanche photodiode for LiDAR receivers that can operate in an eye-safe 2μm band at room temperature. This “breakthrough” achievement eliminates the need for cryogenic conditions that are typically required for vision systems.

The researchers published their peer-reviewed paper in the journal Nature Photonics. It describes their new fabrication process and how their avalanche photodiodes could have useful applications in receivers for eye-safe light imaging, detection, and ranging (LiDAR).

Building the Avalanche Photodiode (APD) 

To build the APD, engineers at UT-Austin utilized molecular beam epitaxy to grow a digital allow made from aluminum, indium, arsenic, and antimony. This alloy combines long-wavelength sensitivity, ultra-low noise, and design flexibility, all crucial properties needed to achieve low dark currents, a capability unavailable with existing low-noise APD materials technologies, according to the researchers. 

“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,” said Professor Seth R. Bank of UT-Austin. 

Through testing and demonstrations, the research team showed that the APD device is capable of operating with very low excess noise and a gain of over 100 at room temperature. In contrast, other state-of-the-art devices demonstrate a gain of only 10 when operating at 125K.

Epitaxial cross section of the avalanche photodiode design.

A cross-section of the avalanche photodiode design (APD). Image credited to Joe C. Campbell

Suited for LiDAR Applications

According to the research team, the APD is “well-suited” for compact, high-sensitivity LiDAR receivers in applications that require high-resolution sensors that can detect greatly attenuated optical signals reflected from distant objects. Examples of such applications include robotics, autonomous vehicles, terrain mapping, and wide-area surveillance. Until now, however, eye safety concerns have limited the adoption of these LiDAR systems because of the higher levels of laser power required to pose a risk of eye damage. 

“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.”

At present, work on the new APD is being transferred to IQE for foundry services and Lockheed Martin for the development of photodiode arrays with readout circuitry. While this takes place, the researchers will focus on achieving low-noise operation at as close to room temperature as possible, which will extend the operating wavelengths further and push sensitivity to the single-photon level.

Source: All About Circuits

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