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posted by Fnord666 on Friday February 19 2021, @07:14PM   Printer-friendly
from the and-it's-a-great-sunscreen dept.

Arthur T Knackerbracket has processed the following story:

A group of researchers from the Fritz Haber Institute of the Max Planck Society and the Humboldt-Universität zu Berlin have found out that a semiconductor can be converted to a metal and back by light more easily and more quickly than previously thought. This discovery may increase the processing speed and simplify the design of many common technological devices.

[...] The scientists involved in this study have investigated the popular semiconductor zinc oxide and figured out that by illuminating it with a laser, the semiconductor surface can be turned into a metal—and back again. This "photo-doping" is achieved by photoexcitation: The light modifies the electronic properties such that electrons suddenly move freely and an electrical current can flow, as it would in metal. Once the light is switched back off, the material also quickly goes back to being a semiconductor.

"This mechanism is a completely new and surprising discovery," says Lukas Gierster, lead author and Ph.D. student in Stähler's group. "Three things in particular have surprised us: For one, photo- and chemical doping behave so much alike despite being fundamentally different mechanisms; two, gigantic changes can be reached with very low laser power; and three, switching the metal on and off happens quickly."

[...] This discovery could be highly beneficial for high-frequency device applications and ultrafast optically controlled transistors by increasing processing speed and simplifying device design. "Our gadgets could become faster—and thus smarter," Julia Stähler says and adds: "Low-power, ultrafast switching of conduction properties will provide us with high speed and design flexibility." She and her group are convinced that the same will prove true for other semiconducting materials, so that their discovery will likely reach much further than just zinc oxide.

Journal Reference:
L. Gierster, S. Vempati, J. Stähler. Ultrafast generation and decay of a surface metal [open], Nature Communications (DOI: 10.1038/s41467-021-21203-6)


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  • (Score: -1, Troll) by Anonymous Coward on Friday February 19 2021, @07:22PM

    by Anonymous Coward on Friday February 19 2021, @07:22PM (#1115017)

    >> Once the light is switched back off, the material also quickly goes back to being a semiconductor.

    Lack of light... what more proof do you need?

  • (Score: 2) by DannyB on Friday February 19 2021, @07:31PM (2 children)

    by DannyB (5839) Subscriber Badge on Friday February 19 2021, @07:31PM (#1115023) Journal

    TFA doesn't say, but if the zinc oxide switches from a semiconductor to more like a metal, could this be used to switch large amounts of power? eg, large amounts of power compared to the power needed for the LED or laser that induces the state change.

    Solid state high power switches have lots of uses. No moving parts is appealing.

    I assume an LED Laser would be a suitable laser? I mean to assume that some exotic type of laser isn't a requirement for this to work. Thus a new type of zinc oxide op-tickle-coupled switch device could be produced.

    Or simply a zinc oxide sensor for an electric eye application using a laser. Since it can work at very high frequency, you could count people who are moving very rapidly through a turnstile, such as to get in to a McDonalds to try the latest new product.

    Also see:
    How an LED works [soylentnews.org]

    --
    People today are educated enough to repeat what they are taught but not to question what they are taught.
    • (Score: 0) by Anonymous Coward on Friday February 19 2021, @10:52PM (1 child)

      by Anonymous Coward on Friday February 19 2021, @10:52PM (#1115099)

      > could this be used to switch large amounts of power?

      According to this, https://en.wikipedia.org/wiki/Zinc_oxide [wikipedia.org] it is fairly transparent, so it seems possible that the laser light could switch a thick layer--which in turn could carry significant current.

      Before looking at the Wiki article, I was thinking that it might only be a surface effect, in which case the conductive layer would be extremely thin (and only carry tiny current for data)...

      • (Score: 2) by c0lo on Saturday February 20 2021, @01:37AM

        by c0lo (156) Subscriber Badge on Saturday February 20 2021, @01:37AM (#1115159) Journal

        Not gonna work in bulk.
        * If it's transparent, the light doesn't interact with the crystal, so no conduction.
        * If it is made conduction by photodoping (they way they did), it's not gonna be transparent - that is, the light are going to be absorbed to cause that electron-hole plasma that creates the metallic conduction energy band. It the light is absorbed, it's gonna be absorbed close to the surface, therefore the bulk is going to stay semiconducting and contribute nothing to the phenomenon you wish.

        --
        https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
  • (Score: 3, Interesting) by c0lo on Saturday February 20 2021, @01:56AM

    by c0lo (156) Subscriber Badge on Saturday February 20 2021, @01:56AM (#1115164) Journal

    Making zinc oxide a conductor is not the news here, it was done in the past many times by chemical and photodoping techniques.
    Photodoping - that's what they used - itself is not new, here's an 1976 [sciencedirect.com] article.

    In fact, the considerations about "This mechanism is a completely new and surprising discovery" are just "Heh, we looked into how photo- and chemical doping work and was surprided that they have the same effect: creating a conduction band". Doh!

    The actual advance they article communicates is that they managed to find a way to obtain an electron/hole plasma with:
    - high efficiency - thus small irradiating powers are needed
    - very short life times, so that very high switching frequencies are possible. The previous ways of doping where creating metastable excited states which maintained conduction for some times after the illumination was switched off.

    The downside - it works up to 256K, which was around the temperature of Texas a few days ago.

    TFDOI:

    In this article, we unveil an ultrafast photoinduced SMT confined to the surface of ZnO using very low excitation fluences with sub-ns decay and feasible up to at least 256 K. This dramatic effect is enabled by photodoping of the surface: depopulation of deeply bound in-gap (defect) states induces transient local downward BB and populates the CB with electrons. Above a threshold fluence of only 13.6 μJ/cm2, the photoexcited electrons delocalize in a non-equilibrium state that shows all defining footprints of a metal:

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
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