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news digest ♦ LEDs


This means a less than 1 K (10C) variation of the GaN surface temperature during InGaN MQW growth.


LayTec’s Pyro 400 is widely used for enabling fab-wide GaN surface temperature uniformity in many LED manufacturers production lines.


Meanwhile, more complex LED structures and tighter cost reduction targets need even more advanced in-situ metrology. Figure 1, below, shows such an example; ternary InGaN and AlGaN layers cause emissivity changes that lead to 0.7 K error of the UV pyrometry reading.


Figure 2: GaN MOCVD view-port before (red) and after maintenance (blue): the transmission at the 400nm detection wavelength of a UV pyrometer is suffering from the window coating (red). The resulting -10K artifact is avoided by Pyro 400 Gen2


Last, but not least, an assisting infrared pyrometer has been integrated into Pyro 400 Gen 2 for simultaneous monitoring of wafer pocket temperature throughout the full LED growth run.


Figure 1: Effect of changing emissivity to UV pyrometer temperature reading: up to 0.7 K errors show up without emissivity correction during growth of a GaN/AlGaN-GaN-SL/ InGaNMQW/ GaN structure


LayTec‘s answer to this challenge is the Pyro 400 Gen 2. Along with in-situ UV pyrometry the new generation tool includes real-time UV emissivity correction for enhanced accuracy of GaN surface temperature during growth of more complex LED structures.


A further challenge to reliable GaN temperature control in HB- LED production is the view-port coating.


Figure 2 shows its effect just before maintenance; the UV transmission of the view-port is significantly reduced and an uncorrected UV pyrometer would give a -10 K temperature artefact. Pyro 400 Gen 2 solves this problem,too. Laytec claims the tool automatically senses and corrects these coatings and enables a long-lasting 24/7 accuracy in HB-LED emission wavelength.


US DOE hails Soraa GaN on GaN LEDs


The firm has been recognised for the development of high- efficiency m-plane LEDs on bulk gallium nitride substrates


Soraa has received a Lighting award from the U.S. Department of Energy (DOE) for its outstanding work in the development of high-efficiency m-plane LEDs grown on low-defect density bulk GaN substrates.


The company demonstrated a very high peak internal quantum efficiency (IQE of 88 percent), low efficiency droop (10 percent from 10Acm-2 to 100A.cm-2) and perfect wavelength stability (up to 200A.com-2) at a wavelength of 450nm LEDs.


“Research and development of LEDs on bulk GaN substrates is one of the critical approaches to the technological development of Solid State Lighting - a sentiment recently echoed by the National Academy of Sciences. We are pleased to recognise Soraa’s pioneering work in this area,” says Jim Brodrick, Manager of the U.S. DOE’s Solid State Lighting Program.


“We are honoured to receive an award from the U.S. Department of Energy and it is a further testament to deep technological expertise that has made us the world’s leader in the development of GaN on GaN LEDs on all planes,” adds Mike Krames, CTO of Soraa.


Soraa’s GaN on GaN LEDs handle more current and emit substantially more light (about ten times) per area of LED


82 www.compoundsemiconductor.net March 2013


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