Extremely low-excess-noise and high-sensitivity APDs developed using AlAsSb lattice matched to InP

A team at Cardiff University led by professor Diana Huffaker - the Sêr Cymru chair in Advanced Engineering and Materials and scientific director of the Institute for Compound Semiconductors (ICS) - has collaborated with the UK’s University of Sheffield and the California NanoSystems Institute at the University of California, Los Angeles (UCLA) to develop an ultrafast and highly sensitive avalanche photodiode (APD) that creates less electronic noise than its silicon rivals (Xin Yi et al, ‘Extremely low excess noise and high sensitivity AlAs0.56Sb0.44 avalanche photodiodes’, Nature Photonics, published 8 July 2019).

Faster, supersensitive APDs are in demand worldwide for use in high-speed data communications and light detection and ranging (LIDAR) systems for autonomous vehicles.

Unfortunately, the indium phosphide (InP) and the indium aluminium arsenide (InAlAs) typically used as the gain material in APDs have similar electron and hole impact ionization coefficients (α and β, respectively) at high electric fields, giving rise to relatively high excess noise and limiting their sensitivity and gain bandwidth product.

Now, the new work has reported extremely low excess noise in an AlAs0.56Sb0.44 APD lattice matched to InP. A deduced β/α ratio as low as 0.005 with an avalanche region of 1550nm is close to the theoretical minimum and is significantly smaller than that of silicon, with modeling suggesting that vertically illuminated APDs with a sensitivity of −25.7dBm at a bit error rate of 1x10-12 at 25Gbs-1 and 1550nm can be realized.

“The innovation lies in the advanced materials development using molecular beam epitaxy (MBE),” says Huffaker. “This particular material is rather complex and challenging to synthesize as it combines four different atoms, requiring a new MBE methodology. The Sêr Cymru MBE facility is designed specifically to realize an entire family of challenging materials targeting future sensing solutions,” she adds.

“The results we are reporting are significant as they operate in very low-signal environment, at room temperature and, very importantly, are compatible with the current indium phosphide (InP) optoelectronic platform used by most commercial communication vendors,” says Dr Shiyu Xie, Sêr Cymru co-fund fellow. “These APDs have a wide range of applications. In LiDAR [light detection and ranging] or 3D laser mapping, they are used to produce high-resolution maps, with applications in geomorphology, seismology and in the control and navigation of some autonomous cars,” he adds. “The material we have developed can be a direct substitute in the current existing APDs, yielding a higher data transmission rate or enabling a much longer transmission distance.”

The Sêr Cymru Group within ICS is now preparing a proposal with collaborators at Sheffield for funding from UK Research and Innovation to support further work.

“The work of professor Huffaker’s Sêr Cymru Group plays a vital role in supporting the ongoing success of the wider compound semiconductor cluster, CS Connected, which brings together industry and academic partners in South Wales to develop 21st Century technologies that create economic prosperity,” comments Cardiff University vice-chancellor professor Colin Riordan.

“Our research produces direct benefits for industry,” Huffaker asserts. “We are working closely with Airbus and the Compound Semiconductor Applications Catapult to apply this technology to future free-space optics communication system.”

Tags: APDs

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