news digest ♦ Power Electronics
will be the quickest to come up with the goods? We want the brightest, eco-friendliest most versatile LED bulb at the lowest cost which is also easy on the eye.
It’s a tall order.
Most white to blue semiconductor LEDs incorporate the wide bandgap compound semiconductor gallium nitride (GaN). And you may be spoilt for choice with the different substrates that can be used in making the device - these include sapphire, SiC, silicon and GaN itself.
Many of these substrates are costly though. The exception is silicon, which comes in large substrate sizes such as 6” and 8”.
So what are the challenges of growing GaN on silicon?
Firstly the difference in lattice parameter between the most prevalent silicon (111) and GaN is large (around 17 percent). One of the key aspects to counter this is growing a layer (often AlN) - this layer prevents chemical reactions between gallium and silicon and makes the wafer behave like a substrate having lattice parameters closer to that of GaN. Then the buffer layer (mainly AlGaN) is grown to further reduce the mismatch.
There is also a 52 percent thermal mismatch between GaN and silicon. This means that once the wafer is cooled down after growth, the GaN will contract at a different rate to the silicon substrate.
Having said that, the plus side would work two-fold. Silicon substrates are cheap and also, growing on silicon would enable fabs to use their existing tools without having to invest in costly alternative equipment.
Current players in the GaN-on-Si market include Toshiba and Plessey. Both companies have recently launched LEDs for the lighting market. But efficiencies are still relatively low.
Using technology initiated by Colin Humphreys’ group at Cambridge, Plessey and Aixtron are working together to optimise a process using a close coupled showerhead (CCS) reactor capable of growing 6 inch GaN-on-Si.
Apart from Toshiba, competitors include Lattice Power, Transphorm, Azzurro, Infineon, Philips Lumileds, Samsung and imec (and partners). Soitec, Azzurro, Kyma, Translucent and EpiGaN provide GaN-on-Si templates.
So only time and investment will tell who comes out on top.
Meaglow to upgrade ALD nitride deposition tool in Turkey
The hollow cathode plasma source reduces the oxygen contamination in ALD systems and increases the quality of thin III-nitride films during growth
Meaglow is to install a hollow cathode plasma source for the 138
www.compoundsemiconductor.net August/September 2013 ALD system converted with a hollow cathode plasma source
Initial results show a significant reduction of oxygen content in compound nitride films grown. Results will be presented October 27th to November 1st at the 224th ECS Fall Meeting in San Francisco, California at an invited talk presented at the symposium on “Atomic Layer Deposition Applications”.
Meaglow is now focused on commercialising its hollow cathode plasma technology which also has the advantage of scalability to large deposition areas. Meaglow is seeking additional ALD system owners and suppliers interested in removing the oxygen contamination in their films.
Kyma uses Nanotronics tool
to classify defects in GaN The newly installed inspection system will be used in the characterisation of Kyma’s growing III-nitride semiconductor materials product line
In May of 2013, Nanotronics Imaging installed an nSPEC
group of Necmi Biyikli, a professor at the Institute of Materials Science and Nanotechnology, at Bilkent University in Turkey.
The plasma source is being used to upgrade their Atomic Layer Deposition (ALD) system by replacing an inductively coupled plasma source. This enhancement will reduce the oxygen contamination in ALD systems and increase the quality of nitride thin films grown.
The III-nitrides grown at the university with the ALD system are used for LEDs and power electronic applications. The actual materials grown using the system are AlN, GaN and InN.
Bilkent University researchers will be presenting some of their findings about suitable applications for these products at the ALD 2013 conference on Wednesday.:
«The Bilkent system was easy to retrofit and the Meaglow Plasma source was the perfect solution for their oxygen contamination problem,» says Butcher, Chief Scientist of Meaglow.
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