Some of today’s silicon devices actually include small amounts of germanium, so using existing manufacturing processes to deposit the material isn’t necessarily difficult. What is difficult is depositing it in uniform layers on top of silicon. The distance between the atoms in a crystal of germanium is different from the distance between the atoms in a crystal of silicon. Combining the two produces strains and cracks, which could cause problems in an electronic device.
The Intel researchers focused on developing a process that minimizes the strain on the materials near the part of the device that detects light. Many of the details are proprietary, but Paniccia explains that his team experimented with a number of variations in the materials’ growth conditions. In the end, the researchers found an ideal combination of temperature and other factors that sweep defects out to the edge of the detector, where they don’t impede performance. “It took us a long time to get there,” Paniccia says. “It’s not a completely new design, but it’s a lot of engineering.”
The team’s next major hurdle is to develop processes for integrating the detector and other silicon devices on a single chip. While Paniccia doesn’t expect integration to pose any major challenges, he says that it could take a while to complete. He adds that, while all three of his team’s silicon photonic devices work well in the lab, when they’re subjected to quality-control testing, problems could arise. He estimates that consumers could begin to enjoy the benefits of integrated silicon photonics within about five years.