According to Brown, scientists have fashioned lasers since 1960 from substances ranging from neon to sapphire. But the structure of silicon would not allow for the proper line-up of electrons to emit light.
The three Brown researchers, led by engineering and physics professor Jimmy Xu, claim to have created the directly pumped silicon laser by changing the atomic structure of silicon. This was accomplished by drilling billions of holes in a small piece of silicon using a nanoscale template, resulting in "weak but true" laser light.
The researchers' results are published in an advanced online edition of Nature Materials.
“There is fun in defying conventional wisdom,” said Xu, in a statement issued by Brown, “and this work definitely goes against conventional wisdom including my own.”
While now possible, Xu said, the silicon laser is not yet practical. In order to make it commercially viable, Xu said, it must be engineered to be more powerful and to operate at room temperature it currently works at 200 degrees Celsius below zero.
But a material with the electronic properties of silicon and the optic properties of a laser would find uses in the electronics and communications industries, helping to make faster, more powerful computers or fiber optic networks, the researchers said.
According to Brown, light emission from silicon was considered unattainable because of silicon’s crystal structure. Electrons necessary for laser action are generated too far away from their “mates,” the university said, and bridging the distance would require just the right “matchmaker” phonon, arriving at precisely the right place and time, to make the atomic connection.
In the past, scientists have chemically altered silicon or smashed it into dust-like particles to generate light emission, Brown said. But more light was naturally lost than created, the university said, so Xu and his team changed silicon’s structure by removing atoms drilling holes in the material.
To get the job done, the team created a template, or “mask,” of anodized aluminum. About a millimeter square, the mask is said to feature billions of tiny holes, all uniformly sized and exactly ordered. Placed over a piece of silicon then bombarded with an ion beam, the mask served as a sort of stencil, punching out precise holes and removing atoms in the process, according to Brown's announcement. The silicon atoms then subtly rearranged themselves near the holes to allow for light emission, it said.
The Defense Advanced Research Projects Agency (DARPA) and the Office of Naval Research funded the work. Xu also received support from the John Simon Guggenheim Memorial Foundation. Sylvain Cloutier a Ph.D. student whom Xu credits for the success of the experiment received support from the Natural Sciences and Engineering Research Council of Canada.