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INDUSTRY GaN SUBSTRATES


TopGaN has produced lasers with Ammono’s GaN substrates that deliver state-of-the-art output powers.


A further virtue of our substrates is their high level of conductivity, which stems from an electron concentration of the order of 1019


cm-3 . This high concentration produces a


lowering of the refractive index in the GaN substrate, enabling a so-called plasmonic effect. This is highly beneficial, because a higher output power results from a lower level of laser mode penetration into the substrate, and enhanced wave-guiding and light confinement within the laser chip. Consequently, it is possible to trim the AlGaN cladding layers while maintaining high-performance. In turn, this leads to a simpler laser diode structure that is: less bowed, thanks to smaller stress generated by lattice mismatch between the AlGaN cladding and the InGaN/GaN quantum wells; and has a lower defect density than conventional devices, which have thicker AlGaN claddings.


Trimming the AlGaN cladding thickness has proven to be highly beneficial for the fabrication of Ammono-GaN 460 nm, blue laser diodes grown by plasma-assisted MBE. This growth technology is ideal for growing quantum structures, because it can realise very sharp interfaces and provide very good control of epitaxy parameters at relatively low temperatures in a non-hydrogen environment. By reducing the thickness of the AlGaN cladding, lifetime of the laser can top 2000 hours. This Ammono-GaN based device, which delivered a maximum output power of 80 mW, delivers outstanding performance for an MBE-grown blue laser diode.


DC and RF characteristic of the Ammono-GaN HEMT(courtesy Institute of Electron Technology, Poland)


Ammono-GaN HEMT cross-section (left) and view from the top (right) (courtesy Institute of Electron Technology, Poland) Copyright Compound Semiconductor October 2014 www.compoundsemiconductor.net 63


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