CAMBRIDGE, MA -- Silicon, the material of high-tech devices from computer chips to solar cells, requires a surface coating before use in these applications. The coating "passivates" the material, tying up loose atomic bonds to prevent oxidation that would ruin its electrical properties. But this passivation process consumes a lot of heat and energy, making it costly and limiting the kinds of materials that can be added to the devices.
Now a team of MIT researchers has found a way to passivate silicon at room temperature, which could be a significant boon to solar-cell production and other silicon-based technologies.
The research, by graduate student Rong Yang and engineering professors Karen Gleason and Tonio Buonassisi, was recently published online in the journal Advanced Materials.
Typically, silicon surfaces are passivated with a coating of silicon nitride, which requires heating a device to 400 degrees Celsius, explains Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering. By contrast, the process Gleason's team uses decomposes organic vapors over wires heated to 300 C, but the silicon itself never goes above 20 C room temperature. Heating those wires requires much less power than illuminating an ordinary light bulb, so the energy costs of the process are quite low.
Conventional silicon-nitride passivation "is one of the more expensive parts, and one of the more finicky parts, in the processing" of silicon for solar cells and other uses, says Buonassisi, an associate professor of mechanical engineering, "so replacing part of silicon nitride's functionality with a simplified, robust organic layer has the potential to be a big win."
Passivation is essential: Without it, silicon's surface is oxidized as soon as it's exposed to air, impeding its performance as a solar cell. "It would oxidize within minutes," Yang says. By contrast, the MIT team has
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology