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Black Silicon Used For Surveillance?

Posted by CmdrTaco on from the that-sounds-naughty dept.

An anonymous reader writes "For the past decade, 'black silicon' has been touted as a way to make super-sensitive image sensors and ultra-efficient solar cells. That's because the material — silicon wafers treated with sulfur gases and femtosecond laser pulses — is much better at absorbing photons and releasing electrons than conventional silicon, at least over certain wavelengths. In 2008, Harvard spinoff SiOnyx went public with its plans to commercialize black silicon. But what happened to those plans? Today SiOnyx revealed in another exclusive that it has raised new venture financing from Microsoft co-founder Paul Allen and other big investors. It also has formed a key strategic partnership to scale up manufacturing of black silicon — and go after markets in security, surveillance, automotive, consumer devices, and medical imaging."

4 of 56 comments (clear)

  1. Any questions? by sevenofdiamonds · · Score: 5, Interesting

    I'm getting my Ph.D researching black silicon. If you have science or engineering questions about it, post them in reply to this comment. I'll check back at around 3 PM EST and will do my best to answer the questions I find then.

    1. Re:Any questions? by sevenofdiamonds · · Score: 5, Informative

      Black Silicon is not made in a deposition process. Instead, ordinary silicon is shot with a femtosecond pulsed laser in the presence of a sulfur-containing gas. The laser causes sulfur to be incorporated while also structuring the surface of the silicon. Thus it changes both the chemical state and physical morphology of the material. I encourage you to check out the following freely available Ph.D thesis for more information: mazur-www.harvard.edu/publications.php?function=display&rowid=648.

    2. Re:Any questions? by sevenofdiamonds · · Score: 5, Informative

      Because thin layers of black silicon can absorb as much light as thick layers of ordinary silicon, it is possible that black silicon solar cells would be cheaper than ordinary silicon solar cells. The reason that the most progress has been made on detectors rather than solar cells is that it is easier to make a profit selling detectors at smaller scale. It is not so much the cost floor that has thus far prevented the appearance of black silicon solar cells, but rather just that it is currently not made at a scale that would lead to affordable solar cells. As technologies are developed for making larger quantities of black silicon, I would not be surprised if it or a related material started finding its way into solar cells. An example response spectrum can be found here: http://www.sionyx.com/advantage.html. Note that this plot shows internal gain, which some variants of the material possess at >2V reverse bias. The response function when running at small 1V reverse bias is comparable to that of ordinary silicon, but extended deeper into the IR (out to 1300 nm instead of silicon's 1100 nm).

  2. Re:Not having RTFA by sevenofdiamonds · · Score: 5, Informative

    The S is typically either SF6 or H2S gas. The wavelength of the femtosecond laser isn't especially important; the key is that the laser fluence (energy per area) be above the ablation threshold of the silicon (between 0.1 and 1 J/cm^2 for the relevant pulse durations). The laser spot size is typically a fraction of a millimeter on a side, but it can be rastered over a silicon wafer to make a large-area black silicon film. There is a recent Ph.D thesis available for free at: mazur-www.harvard.edu/publications.php?function=display&rowid=648 that gives a complete recipe for making black silicon.