Info
Info
News Article

Green Light For Laser Diodes?

Researchers at a small, Canadian start-up have unveiled simple test structures that emit incredibly bright green light. Have they filled the green gap, asks Compound Semiconductor.


 



As organisations worldwide race to commercialise a direct green laser diode to plug the much-coveted green gap, Canadian start-up Meaglow could well reach the finishing line first, and with a truly unique approach.

The company recently developed a series of test InGaN p-n junctions, which in the words of chief scientist, Scott Butcher, “are a hell of a lot brighter than any pn junction I've seen in nitrides before." So how have Meaglow researchers achieved this?

The company's test structures are grown using a novel technique called migration enhanced afterglow that circumvents the shortcomings of MOCVD and MBE growth. Based on methods of migration enhanced epitaxy developed for MBE, the technique involves saturating a substrate surface with the active metal to ensure high quality crystal growth can take place at the low processing temperature of 550°C. Crucially, this all takes place in a CVD environment, and with a high pressure 2Torr, scalable hollow cathode plasma source.

As Butcher explains, the method works well for several reasons. Low growth temperatures alleviate epiwafer bow on large diameter wafers that typically takes place during high temperature MOCVD growth processes. Meanwhile, maintaining a CVD environment removes the wide area deposition issues that plague MBE.

Factor in the company's high intensity hollow cathode plasma source - that side-steps oxygen contamination associated with other plasma sources - and you have an effective route to fabricating InGaN laser diodes.

“By processing in the CVD environment, we can go to higher pressures than we could with MBE, which also turns out to be very important for high indium content structures," adds Butcher. “[During deposition] we have a lot more gas collisions with the plasma source, eliminating more of the energetic species that damage the films."

And the results look good. The researchers recently worked with McGill University, Quebec, to produce InN layers, which as Butcher puts it: “had some of the sharpest, low temperature, PL ever achieved." They then went onto produce thick - 50 to 250nm - InGaN layers approaching device smoothness, and have constructed simple p-n junction structures to test the electroluminescence.

These structures consisted of 170nm thick, n-type InGaN layers grown on MOCVD p-GaN buffer layers, on sapphire. Part of the p-GaN was masked during growth to provide a step on which to mount an electrode while a second electrode was placed directly onto the InGaN layer.

Butcher has been genuinely shocked by the results. “These structures blow me away they are so bright," he says. “I'm not sure we understand everything that's happening here and we're still looking at why they are so luminescent."

What is clear at this stage however, is that growing thick, higher In content GaN layers, seems to reduce - to a certain extent - the strains that typically arise from lattice mismatches between the GaN and InGaN layers. “If we grow our layers directly on sapphire we see segregation, so growing on the MOCVD template is one way around this," he says. “However, even with this, we still see the effects of strain on the thin GaN layers. But now we find we're able to grow the layers thick enough to ignore this effect."

So where next for the Canadian start-up? According to Butcher, his team are now collecting electroluminescent spectra for a number of InGaN composition and is also working on fabricating multi-quantum well structures. Devices will also be built with p-type GaN at the top, rather than growing on this layer.

“I think we'll be able to fabricate quantum well [structures] by the end of the year and we'll start seeing some nice bright devices," says Butcher. “Our technology has produced some the of best results to date for higher indium content InGaN... it has really caught a lot of attention as emission is right in the green gap."



Image caption:
The yellow emission as shown is from a high carrier concentration sample whose emission is broadened by a Moss-Burstein effect.




AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.

REGISTER FOR FREE

VIEW SESSIONS

Info
×
Search the news archive

To close this popup you can press escape or click the close icon.
×
Logo
×
Register - Step 1

You may choose to subscribe to the Compound Semiconductor Magazine, the Compound Semiconductor Newsletter, or both. You may also request additional information if required, before submitting your application.


Please subscribe me to:

 

You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in:
 
X
Info
X
Info
{taasPodcastNotification}
Live Event