Optical pulses, which appear as a flash of light, are used to transmit information in high speed optical fibers, and are increasingly used in Light Detection And Ranging (LIDAR) for 3-dimensional imaging. Both of these applications demand light sensors or photodiodes that are capable of detecting very low levels of light intensity down to a few photons, where a single photon is the quantized energy unit of light.
A newly published paper, “Extremely low excess noise avalanche photodiode with GaAsSb absorption region and AlGaAsSb avalanche region,” in Applied Physics Letters, details a discovery by a Sheffield research team that has the capability to transform a single electron at its input to a cascade of electrons at its output.
This multiplication process is commonly known as avalanche breakdown, while a photodiode incorporating this process is called avalanche photodiode (APD). Though the application of reverse voltage, avalanche photodiodes (often referred to as APDs) have internal gain, which means that when compared to PIN-photodiodes they typically have a higher signal-to-noise ratio.
However, the team’s newly designed photodiode exhibits high multiplication factor with very little added noise. The measured noise factor at a multiplication factor of 20 is at least three times lower than a commercial avalanche photodiode. Less noise in this context means that there is less interference in the recognition of signals, and the photodiode is therefore more useful due to increased sensitivity.
In the published paper, the team of researchers from the Department of Electronic and Electrical Engineering, led by Head of Department Professor Chee Hing Tan, demonstrated that they can combine a new semiconductor alloy with a wider bandgap semiconductor AlGaAsSb multiplication region. The new semiconductor alloy is based on a GaAsSb absorption region that has excellent detection efficiency at infrared wavelengths (up to 1,700 nanometers).
This research is a major breakthrough in infrared APD as commercial APDs based on InP have reached their limits since the 1990s. The team led by Prof. Tan, first introduced AlGaAsSb based APDs and showed their low noise performance in 2012 and has since continuously improved the performance using a number of designs. The wafers were grown by the EPSRC National Epitaxy Facility at Sheffield.
In this work, the wafers were transformed into devices by Tarick Blain while Ye Cao performed the measurements and modeling. Additional support in modeling, measurements and analysis were contributed by Jonathan Taylor Mew, Longyan Li and Jo Shien Ng, illustrating the importance of crucial contribution of effective teamwork to the research carried out in the Department of Electronic and Electrical Engineering at the University of Sheffield.
Speaking about the research and the publication of this ground-breaking article in the field of infrared avalanche photodiodes, Professor Chee Hing Tan said, “One of the longstanding limitations of infrared APDs is a relatively high added noise from the multiplication process that limits the maximum multiplication factor. This in turn prevented infrared APDs from reaching the performance limit predicted by established models.
“Our breakthrough result, with an excess noise factor of 2.48, is approaching the theoretical lower limit of 2. This provides the pathway to realize extremely low noise APD that I believe can generate step changes in optical communication and long range LIDAR.”
More information:
Ye Cao et al, Extremely low excess noise avalanche photodiode with GaAsSb absorption region and AlGaAsSb avalanche region, Applied Physics Letters (2023). DOI: 10.1063/5.0139495
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University of Sheffield
Citation:
New photodiode with extremely low excess noise for optical communication and long range LIDAR (2023, February 9)