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Old 02-07-2009, 05:39 PM #1
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Default Nanowire wafer tunes over 200 nm


Top: a real-colour image of the emission from the nanowire wafer. Bottom: emission spectra measured at 16 spots along the length of the wafrer, showing spatial wavelength tunability of 200 nm. (Image credit: Cun-Zheng Ning)

A single semiconductor laser chip with a tuning range of 200 nm has been unveiled by researchers at Arizona State University, US. The device tunes between 500 and 700 nm, a record-breaking performance according to research leader Cun-Zheng Ning. (Nano Letters doi: 10.1021/nl803456k)
Widely tunable semiconductor lasers could be deployed in applications as diverse as spectroscopy and telecommunications to on-chip biological and chemical detection. Achieving such a widely tunable laser has been difficult however due to the limited lattice mismatch permitted by standard epitaxial-based approaches.

The emission wavelength of a semiconductor source depends on the material's bandgap. Widely tunable lasers require alloy semiconductors with similarly tunable bandgaps, which are determined by the alloy composition. In this case, lattice mismatch with the chosen substrate is the limiting factor.
With nanowire technology, Ning and colleagues say that the lattice mismatch limitation can be relaxed or removed completely. This means it is possible, in principle, to grow alloy semiconductors of widely changing composition on a single substrate.

By carefully controlling parameters such as the growth temperature, the team successfully fabricated ternary alloy CdSxSe1-x nanowires where the composition x changed from 0 to 1 continuously from one end of the substrate to the other. As a result, the wafer had a continuous spatial grading of bandgaps between 1.75 and 2.5 eV, or in terms of the wavelength, between 500 and 700 nm.

Since the wafer is covered by nanowires that individually act as nanolasers, numerous such nanolasers of continuously tuning wavelength are formed by a single growth on a single substrate. Under optical pumping, the team was able to show lasing behaviour at each spot along the wafer's length.

Ning's research group is currently working to extend the tunability to an even wider wavelength range and is developing several applications of its unique alloy materials in solar cells, detection, lighting and displays. Many more applications will open up once such lasers are made electrically driven.


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Old 02-09-2009, 02:25 AM #2
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Default Re: Nanowire wafer tunes over 200 nm

Does this mean an adjustable wavelength single laser diode?!

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Old 02-09-2009, 03:14 AM #3
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Default Re: Nanowire wafer tunes over 200 nm

Thanks, I was just looking for something like this.
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Old 02-09-2009, 04:53 AM #4
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Default Re: Nanowire wafer tunes over 200 nm

Quote:
Originally Posted by rocketparrotlet
Does this mean an adjustable wavelength single laser diode?!

-Mark
No, not an adjustable single diode. What they showed is they can make a single diode of any single wavelength; but once made, it won't change. They just made every wavelength across the length of the wafer.

A couple of key points about this, though: 1st, it's only optically pumped. It's a BIG jump to go from optical pumping to electrical pumping. Big jump, not trivial at all, and there's no guarantee it'll even be possible.

The other thing is that it's CdSSe, a II-VI semiconductor. II-VI materials have been explored for a long time, and in fact, II-VI semiconductors were used to make a green laser diode before GaN was ever made to work for violet or blue laser diodes. But there's a reason that we're not using II-VI materials, and that every LED and laser diode in use today are all made from III-V materials: because II-VI materials have never worked well enough to actually be manufactured.

I'm glad people have continued to work on them, because you never know. People once said GaN would never work, and look where we are with it today because a person or 2 wouldn't listen to everyone who said it wouldn't work. But I'm not holding my breathe for II-VI materials to every become viable for laser production.
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