Silicon APD Outperforms InP

By creating a silicon photonics device that outperforms traditional avalanche photodetectors containing expensive, exotic optical materials, researchers said they have moved a step closer to making very low cost optical parts for supercomputing, data center communications, consumer electronics, automotive sensors, medical diagnostics, and other applications.

A packaged silicon avalanche photodetector held in a pair of tweezers. A silicon chip is mounted in the circle on the upper right, while electrical pins on the lower left allow researchers to interface the device with test equipment. (Photos: Intel)

Silicon photonics is an emerging technology using standard silicon to send and receive optical information among computers and other electronic devices by using light instead of electronics. A team of researchers, led by scientists at Intel Corp., used a germanium-silicon avalanche photodetector (APD), a light sensor that detects light and amplifies weak signals as light is directed onto silicon.

Photodetectors are used to "see" optical signals and convert them to electrical ones, but are expensive. For example, a traditional APD made using indium phosphide (InP) can cost $100 or more for a single device. It had been assumed that these devices perform better than silicon, and so are worth the extra expense, but this new research shows that's not the case.

"We've now proven a new device, an avalanche photodetector, that has better performance than any device previously done in this exotic material, or optical material, called indium phosphide," said Mario Paniccia, PhD, Intel Fellow and director of the company's Photonics Technology Lab. "This research result is another example of how silicon can be used to create very high-performing optical devices. In addition to optical communication, these silicon-based APDs could also be applied to other areas such as sensing, imaging, quantum cryptography or biological applications."

A ladybug crawls across an experimental avalanche photodetector chip containing silicon optical devices that are only a fraction of a millimeter in size.

Ultrafast transfer of data will be essential for future computers powered by many processor cores. Silicon photonics-based technology could deliver higher-speed mainstream computing at a lower cost. The team created the silicon-based APD device using silicon and CMOS processing to achieve a "gain-bandwidth product" of 340 GHz -- the best result ever measured for this key APD performance metric, Intel said. This opens the door to lower the cost of optical links running at data rates of 40 Gb/s or higher.

Intel worked with industry and academic collaborators, and the research was jointly funded by DARPA. Intel's flash memory spinoff, Numonyx, provided manufacturing and process development. Professors Joe Campbell of the University of Virginia and John Bowers of the University of California, Santa Barbara, both APD experts, provided consultation and assisted with testing.

A packaged silicon avalanche photodetector. The silicon chip is the grey square in the center of the image. Wire-bonds connect the device to the package pins, which in turn allow researchers to interface the device with test equipment.

The research also builds upon previous breakthroughs announced by Intel, such as fast silicon modulators and hybrid silicon lasers. Combining these technologies could lead to the creation of entirely new kinds of digital machines capable of much better performance than today's machines, Intel said.

The research results were published this week in Nature Photonics.

For more information, visit: www.intel.com