Photodiode operates in eye-safe 2μm band at room temperature

May 29, 2020 //By Julien Happich
Electrical and computer engineers at the University of Virginia and University of Texas-Austin have developed an avalanche photodiode that operates in the eye-safe 2μm band at room temperature, breaking away from the cryogenic conditions typically required for vision systems relying on such devices.

This breakthrough comes from a long-standing collaboration between Joe C. Campbell, Lucien Carr III Professor of electrical and computer engineering at UVA, and Seth R. Bank, Cullen Trust Professor at UT-Austin. Andrew H. Jones, a 2020 Ph.D. graduate advised by Campbell, and Stephen D. March, a Ph.D. student in Bank's research group, contributed to the research.

The team used the novel optical and electrical characteristics of a digital alloy created in Bank's Laboratory for Advanced Semiconductor Epitaxy. Bank employed molecular beam epitaxy to grow the alloy, composed of aluminum, indium, arsenic and antimony. The alloy combines long-wavelength sensitivity, ultra-low noise, and the design flexibility that is needed to achieve low dark currents, which is not available with existing low-noise avalanche photodiode materials technologies.

"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," explained Bank.

Epitaxial cross section of the avalanche photodiode design.
Doping concentrations are given in cm-3 Credit: Joe C. Campbell.

In a paper published in Nature Photonics under the title “Low-noise high-temperature AlInAsSb/GaSb avalanche photodiodes for 2-μm applications”, the researchers report a novel avalanche photodiodes device based on a separate absorption, charge, and multiplication design. The device was demonstrated to operate with very low excess noise (k ≈ 0.01) and a gain over 100 at room temperature (compared to a gain of only 10 for other state-of-the-art devices operating at 125K).

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