LEDs on Silicon Gaining Traction

Plessey has achieved 120 lumens/Watt light output with its MAGIC GaN-on-Silicon LED technology. Light output efficiency was said to be greater than 50%. Engineering samples are shipping now, as well as blue die with a wavelength of 455nm.

CTO Keith Strickland said, “Whilst 120 lumens per Watt for an LED may be considered ‘acceptable’ to industry, we must remember that we have doubled our LED light output in the past six months. I see no reason why we cannot reach state of the art in LED die output performance within the next six months”.

Separately, the Nikkei reports that Samsung Semiconductor Europe plans to manufacture blue LED chips on silicon substrates, with a diameter of 200mm. The chips will be used with phosphors to create white LEDs.

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Blue LED chips are usually made using sapphire substrates, so the use of silicon is interesting – especially as two separate companies have made announcements in the same month. Plessey did not give a reason for its use of silicon, but Samsung said that the silicon substrates’ diameters could be ‘easily increased’ to lower cost.

Challenges facing companies using silicon for blue LED chips include:

* A different linear expansion coefficient to gallium nitride (GaN), causing cracks in the GaN-based semiconductor layer in the cooling process;

* High dislocation (crystal defect density) in the GaN-based semiconductors; and

* Difficulty with increasing yield rates. (TA)