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INDUSTRY GaN DEVICES


At imec, an internationally renowned microelectronics research centre based in Leuven, Belgium, we are addressing these challenges. We are developing an epitaxial process for the growth of GaN on 200 mm silicon, while many vendors active in this area are focusing on the smaller 150 mm platform. Our expertise in GaN is considerable, as we have spent more than a decade developing GaN devices: depletion-mode and enhancement-mode power transistors, power diodes, and other types of devices, such as air sensors and LEDs (see Figure 1). We share the technology that we have developed with today’s and tomorrow’s partners, so that they can use this to design and produce their first devices in-house or at imec.


By carefully optimising each of the layers in our GaN-on-silicon structures, including the key buffer layer, we have been able to form


epiwafers with a low defect density and smooth surface. According to atomic force microscopy measurements on areas of 5 μm by 5 μm, the surface has a root-mean-square roughness of just 0.4 nm.


From a manufacturing perspective, producing a few good-quality 200 mm GaN-on-silicon wafers is promising, but this will not amount to much unless it is followed up with a demonstration of long-term reproducibility. We have done just that, using various measurements to determine the quality and reproducibility of our buffer layer in structures grown on a MaxBright Veeco reactor. Crystal quality of the buffer layer shows small variation from wafer to wafer, according to X-ray diffraction measurements with a Jordan Valley QC3 tool (see Figure 2a). What’s more, the average of the full-width-at-half-maximum (FWHM) for the AlGaN buffer is among the best reported in literature,


Copyright Compound Semiconductor October 2014 www.compoundsemiconductor.net 49


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