DEC 13, 2013 12:00 AM PST

Nanowire Lasers Show Promise For Real-World Applications

WRITTEN BY: Jen Ellis
One of the most difficult aspects about nanotechnology advancements is integrating laboratory achievements into real-world applications. Many experiments show promise in the lab, and can theoretically be produced in an industrial environment, but have limiting properties that keep them from making the final leap into commerce.

In the semiconducting world, one of the primary tradeoffs is performance under ambient temperature conditions. With this in mind, scientists at the Technical University of Munich (TUM) in Munich, Germany have developed nanowires containing Group III-V semiconductor materials that can act as nano-scale lasers and operate at room temperature. These light-emitting wonders were introduced in the journal Nature Communications, and further explored in Nano Letters, where improved performance was demonstrated in both electronic and optical applications.

The possible applications are not limited to traditional electronic and optical fields. Nanowires have very high sensitivity (in part because of their inherently large surface-to-volume ratio), and depending on the size of nanowire created, they may be capable of entering biological cells. This combination opens up interesting possibilities in sensors for environmental and biological applications, perhaps allowing effective monitoring of sensitive biosystems that are currently impossible to monitor.
The TUM research team used the more forgiving nature of nanowires (as compared to producing films or bulk crystals) to produce a "core-shell" construction that optimizes the different Group III-V components. The resulting nanowires are about one-thousandth of the thickness of a human hair, and have a bandgap tailored to emit in the near-IR wavelengths (making them well suited for fiber-optics). Further, they can act as both lasers and waveguides.

Since they are capable of being grown directly on silicon wafers, the nanowires are compatible with existing manufacturing processes-and because of their small diameters (around 10-100 nm), issues with mismatching of crystal lattices can be avoided during the growth process. This combination could represent a future breakthrough in industrial-scale silicon-based photonics.

However, it's far too early to declare victory for this technology-for a number of reasons.

The laser output from the TUM nanowires (as well as similar materials reported by the Australian National University) was produced by light stimulation-and in the field electrical stimulation is going to be the most likely mechanism. There's no guarantee that the same performance can be achieved under those conditions.

With respect to manufacturing, the precise growth mechanism will require significant capital equipment investment to achieve tight manufacturing tolerances at higher scales. Currently, there are very few facilities that are capable of producing these materials at all, much less at scale. Basic economics could limit the use to high-value added or military applications. (Even so, other technologies have made similar leaps in the past-if the performance is superior, industry will find a way.)

Of course, safety and regulatory concerns will be another hurdle to overcome-especially for materials small enough to penetrate cells. Expect the US EPA and other regulatory agencies to give this the same scrutiny and restrictions as other nanotechnology advancements, potentially adding extended testing time and costs.

Room-temperature operation and compatibility with existing processes make this technology promising enough to warrant further research. Work is continuing in optimizing processes, exploring electrical activation methods, and integrating and characterizing their performance in typical photonics devices and platforms. Keep an eye on this interesting technology as it tries to make its way from the lab to the marketplace.

Image: NanotechWeb
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