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INDUSTRY GaN SUBSTRATES


performances of devices made on different types of substrate may be bigger than the variations between those made on GaN, the quality of the native substrate does still have a big impact on the attributes of the resulting chip.


The majority of GaN substrates sold today are formed by depositing a thick layer of this material by HVPE to form a GaN crystal, and then slicing this up. Manufacture by this approach, which is employed by the likes of Sumitomo, Hitachi and Mitsubishi, produces a substrate that is not perfectly flat, because at some point GaN growth had to be initiated on a non-native substrate. What’s more, the defect density in these substrates is far higher than that found in InP and GaAs substrates – it is typically in the region of 106


cm-2 .


GaN substrates with a far higher material quality are possible with the ammonothermal growth technique that we pioneer at


Ammono of Warsaw, Poland. Our approach involves the growth of Ammono-GaN crystals in an autoclave containing GaN seeds, ammonia, and alkali metal amide mineralizers. Heating this concoction to around 550 °C, while maintaining it at pressures of typically 5000 atmospheres, leads to the growth of GaN crystals with a dislocation density that can be as low as 103


cm-2 . They can be sliced into crystals that are exceptionally flat.


We are currently scaling up our production of GaN crystals to serve our customers, which number more than a hundred. By building bigger autoclaves, we can grow bigger crystals and increase the size of our substrates from 2-inch – our standard offering today – to 4-inch. The industry will eventually move to even larger substrates, and there is no fundamental reason why we cannot move accordingly, by producing 6-inch and then 8-inch material.


Copyright Compound Semiconductor October 2014 www.compoundsemiconductor.net 61


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