editorialview by Dr Richard Stevenson, Editor Transforming telecom lasers
THERE ARE MANY PATHS you can go down when striving to improve device performance.
One option is to keep it simple and try to improve the quality of the production processes, such as optimising the growth of the epiwafer. This can pay dividends, particularly if the class of device is not well established.
If you are up for more of a challenge, you can try to boost performance by altering chip design. Such an effort, which can be supported by simulations, could involve modifying the device architecture, such as increasing the doping in one layer.
But by far the most radical route is to dispense with a mature material system, and adopt one that is yet to be tried and tested. That’s what a team of European researchers is doing, developing telecom lasers based on bismuth alloys, rather than InP. This effort has had to start from scratch, developing models to understand device behaviour and establishing appropriate growth conditions before it is even possible to try and fabricate the first devices (see feature on p53 for details).
The rewards for these trailblazing researchers could be huge. InP laser efficiency is impaired by Auger recombination, and this inherent interaction generates lots of heat. But with bismuth alloys, the spin-off splitting energy can rule out the possibility of Auger recombination if the bismuth content in the alloy exceeds
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10 percent. The promise of telecom lasers that are free from cooling is incredibly appealing. It’s not just the potential to cut costs by eliminating the need for coolers – it’s the substantial energy savings that could result.
That’s because internet traffic is rocketing, due to uptake of smartphones and internet TV, and if energy-saving measures are not introduced, this traffic could start to be responsible for a significant proportion of the world’s carbon footprint. So I, for one, hope that this group of pioneers succeed in their efforts.
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