Academics from the University of Sheffield teamed up with the University of Cardiff and the University of California and Los Angeles (UCLA) in an extended study of compound semiconductor alloy consisting of Aluminium-Arsenide-Antimonide ( AlAsSb) to produce an optical sensors that produces very high internal gain, called avalanche gain. Unlike many other semiconductor materials, AlAsSb exhibits high avalanche gain without introducing excessive noise. Since it can be grown on widely used commercial Indium-Phosphide (InP) substrate, there is tremendous potential to combine AlAsSb with an infrared absorbing semiconductor layer made of Indium-Gallium-Arsenide (InGaAs) to produce a new class of infrared avalanche photodiodes (APDs).

APDs are extremely sensitive semiconductor devices that manipulate the “photoelectric effect” to convert light into electric current, which is amplified by the avalanche gain. Globally, faster and supersensitive APDs are sought-after for use in high-speed data communications and light detection and ranging (LIDAR) systems for autonomous vehicles

The performance of InGaAs/InP APDs has historically been limited by the noisy multiplication process in InP. This is because both electrons and holes could initiate the multiplication process but with random probabilities. Hence InGaAs/InP APDs are significantly noisier than the Silicon APDs used in the visible wavelengths. The potential of using AlAsSb was first demonstrated at Sheffield in 2012, when the team led by Professor Chee Hing Tan reported that AlAsSb can exhibit high gain with similar noise performance to Silicon APDs. This low noise performance is attributed to the finding that electrons dominates the multiplication process in AlAsSb.

Recent work at the partner universities has shown that when a thicker layer of AlAsSb is used to produce avalanche multiplication, the electron initiated multiplication process becomes so dominant such that holes play insignificant roles, leading to dramatically reduced noise.

Professors Chee Hing Tan and John David from the Advanced Detector Centre at the University of Sheffield are confident that based on the measurement of avalanche gain and noise results AlAsSb has the potential to outperform Silicon.

Professor Chee Hing Tan says ‘This is a major step towards achieving optical sensors with near perfect internal gain mechanism that can lead to step changes in applications ranging from low light level sensing in future 6G optical based communication and optical spectroscopy, to single photon detection in quantum applications.’

Professor John David added that, “We have now extracted the most important material parameters that will enable us to design high-sensitivity, high-speed APDs operating at the infrared wavelength of 1550 nm. These will be a key component in LIDAR systems for autonomous vehicles and for other sensing applications.”

For more details on this project please follow the link to the paper the team had published in ‘Nature Photonics’

If you have any questions regarding this project or research area please contact Professor Tan on or Professor David on