By Accident, Harvard Scientists Create Black Silicon

Physics professor Eric Mazur was worried.

His research grant for semiconductors from the Army Research Office was coming up for renewal, and he needed to actually do some research related to semiconductors if he wanted to avoid getting himself in hot water.

After rummaging around in one of his supply cabinets, he found some wafers of silicon that were lying around from a previous project.

A bit more foraging by one of his graduate students unearthed a tiny bottle of gas that Mazur himself had used when he was a postdoctoral fellow at Harvard. Had the graduate student known that this gas was particularly stable—unlikely to react with other chemicals—he might not have used it.

The graduate student put the silicon wafers and the gas in a chamber and shot them with short, intense laser pulses—the focus of Mazur’s research at the time. “The rest,” Mazur said in a recent interview, “is history.”

The reaction performed by Mazur’s graduate student accidentally created black silicon, a semiconductor that is ultra-sensitive to light and may have application in devices from night-vision goggles to photovoltaic solar panels.

This type of unintentional discovery is not unusual in science, according to Michael J. Hawley, a researcher and entrepreneur who is on the board of Mazur’s startup.

“The most interesting word in science at something and you see something strange and you think, ‘Huh, that’s funny.’”

TRAPPING LIGHT

The graduate student who was performing the experiment, Tsing-Hua Her, noticed immediately that something was amiss when he combined the silicon with halogen gas: the silicon had turned black, but the material couldn’t have been burned, since there was no oxygen present in the chamber. Under the microscope, Her and Mazur saw, the surface of the wafers displayed a forest of tiny spikes.

“There was something really special about this material,” Mazur said.

The black silicon had phenomenal light absorption sensitivity in both the visible and infrared regions, according to Mazur. By contrast, normal silicon does not readily absorb infrared light.

As the work turned from the excitement of the initial discovery to figuring out how the material could be used in devices, a graduate student named James E. Carey joined Mazur’s lab.

“I just started working away and began making some really good early prototype devices,” Carey said.

Carey wanted to work in industry and had envisioned starting a company in the future, so Mazur suggested they go into business together.

“Our first task was to make sure that we carefully understood how the technology would be made available to different industries and how it delivers benefit in different applications,” said Stephen D. Saylor, the chief executive of SiOnyx, the start-up venture created to commercialize the innovation. “That was what the company was doing for the last year and a half.”

SiOnyx is now moving forward with commercialization, targeting industries in which a start-up with neither a huge sales staff nor a well-established product line can find companies to partner with. Some of these areas might include medical imaging, commercial imaging, and power generation, Saylor said.

The high light sensitivity of a detector like black silicon could allow patients to be subjected to less radiation during medical imaging, allowing physicians to produce better images with less damage to the patient’s health. Similarly, digital cameras with more sensitive lenses could capture better quality images in low-light situations, and the technology might enable the development of a cheap and effective night-vision device.

The discovery could also allow for more efficient solar cells, since using black silicon would allow panels to harness a broader spectrum of light.

“Black silicon is essentially a new photonic material,” Saylor said. “Everyone who looks at our technology is very excited about the potential it has in solar power generation.”

FROM BENCH TO BOARDROOM

When Mazur and Carey decided to commercialize their discovery, neither of them had any experience in business.

Unlike large pharmaceutical corporations, who often license medical devices or drugs developed in university biomedical research labs, the scientists had no program waiting for them to help them commercialize their research.

“The first two things are to make sure you have the rights to the technology and try to raise money,” Carey said.

In concert with Harvard’s Office of Technology Development, Mazur and Carey patented their discovery and built up SiOnyx, pioneering a business model followed by 11 more Harvard-related start-ups created just this past year.

As a breakthrough in material sciences, the creation of SiOnyx reflects an uptick in technology transfer in the physical sciences, according to Alan D. Gordon, the director of business development for the Office of Technology Development. Traditionally, most technology transfer, particularly at Harvard, has been among life science researchers.

Gordon said that one of the ways that Harvard hopes to increase technology transfer for the engineering and physical sciences is to create a dedicated program similar to the Accelerator Fund for the Life Sciences, which provides funding for promising, but early-stage discoveries that need “proof-of-concept” validation before venture capital or other industrial partners will make a significant investment and develop it for commercialization.

Given the breadth of products that black silicon could be used for, Mazur said, it’s evident that semiconductors have wide commercial applications.

“It’s not an overstatement to say that the modern world is dominated by semiconductors,” he said.

—Staff writer Alissa M. D’Gama can be reached adgama@fas.harvard.edu.

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