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TECHNOLOGY GaN SUBSTRATES


high crystalline quality of this material, but also its very high purity.


Additional measurements by the NCSU team revealed that the room- temperature transmission spectrum was relatively featureless up to the band edge (see Figure 6b). What was even more impressive was that, according to secondary ion mass spectrometry, oxygen and carbon contents were below 1016


cm-3 level was 3 x 1016


, while the silicon impurity cm-3


. In addition,


the substrates had a high surface quality, according to low-temperature photoluminescence and high-resolution X-ray studies of the diffuse scatter and crystal truncation rods.


These measurements confi rmed that the work has laid the foundation for the manufacture of high-quality, larger GaN crystals that can be cut into wafers with the well-defi ned and uniform offcut that device makers are looking for. However, that’s not to say that the research in this area is over. Next, the scientists at IHPP PAS want to examine doping via HVPE,


Fig. 6: Photoluminescence spectra obtained at 3K from the (0001) surface of the freestranding HVPE-GaN (linear scale); b) RT transmission spectrum of the freestanding HVPE-GaN (courtesy of Z. Bryan and I. Bryan, NCSU).


to see if it is possible to create semi- insulating and n-type substrates with controlled doping levels. It is also needed to transfer the process to 2-inch material. As IHPP PAS do all this, Ammono will be optimizing their ammonothermal GaN growth on these HVPE crystals, to increase the production and availability of ultra-high-quality GaN substrates.


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Further reading T. Sochacki et. al. Appl. Phys. Express 6 075504 (2013)


T. Sochacki et. al. Journal of Crystal Growth 394 55 (2014)


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