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INDUSTRY GaN SUBSTRATES


Fantastic


foundation yields great devices


GaN substrates formed from ammonothermal growth underpin the fabrication of devices delivering outstanding levels of performance


BY PIOTR WILINSKI FROM AMMONO


IF YOU WANT to make a great GaN device, you must start off with a native substrate. By doing this and thus employing homoepitaxial growth, issues associated with differences in thermal and lattice mismatch are eliminated, so the epiwafers are flat and material quality high.


A native substrate is actually the only option for growing ultraviolet, blue and green lasers – all alternative foundations lead to material quality that is insufficient for the manufacture of commercial products. Due to this monopoly, it is not that surprising that for the makers of GaN substrates, shipments to laser diode manufacturers account for a high proportion of sales. Lasers formed on these substrates feature in the read and write heads Blu-ray players and recorders, and shipments of edge-emitting chips should increase as they are deployed in optical laser displays, laser TVs, movie projectors and pico- projectors, printers, and lithography systems.


In comparison to the laser, the LED is a less demanding device, capable of delivering good performance with material of lesser quality, formed via GaN growth on a foreign substrate. However, for really high levels of performance at very high currents densities, a GaN substrate is invaluable. Soraa, Panasonic and Seoul Semiconductor use this foundation to make LEDs, and are causing something of a stir with devices delivering very high output power densities, while suffering from relatively little droop – the decline in device efficiency with increasing current. GaN substrates are also valued in the electronic domain. Armed with this foundation, engineers can turn to vertical device architectures and produce smaller chips with higher breakdown voltages, higher power densities and higher signal frequencies.


Variations in quality


It would be easy – but wrong – to think that all GaN substrates would yield the same results. While differences between the


60 www.compoundsemiconductor.net October 2014 Copyright Compound Semiconductor


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