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Kyma raises the bar for GaN thermal conductivity


KYMA TECHNOLOGIES, supplier of crystalline AlN and GaN and related products and services, has announced results of an analysis of the thermal conductivity of several of its GaN based products. The thermal conductivity analysis was carried out over the past three years by researchers in the group led by John Muth of the Materials Science and Engineering Department of North Carolina State University. Muth’s group has published many of the results during this three year period for bulk and template single crystal GaN materials. More recently Muth’s group also measured the thermal conductivity of Kyma’s high purity polycrystalline GaN.


Kyma says the results indicate that its products have beaten two records. Firstly, its bulk GaN has been measured to have thermal conductivities in the range of 260 ± 5 W/mK. Also, its high purity polycrystalline GaN has been measured to have thermal conductivities in the range of 165 ± 5 W/mK.


Additionally, the thermal conductivity of Kyma’s GaN on sapphire templates is found to vary from 180 W/mK to 220 W/mK for thicknesses between 100 microns and 400 microns, respectively, a result of declining dislocation density from approximately 8 x 108cm-2 to 3 x 107cm-2,


respectively. Kyma’s more typical GaN template product has 5 microns of GaN thickness and was not measured but is expected, based on NCSU’s analysis of the literature, to have a thermal conductivity of approximately 130 W/mK, which Kyma says is ~20 percent higher than typical values for a 2 micron thick MOCVD GaN buffer layer grown on sapphire.


While defect density clearly impacts bulk GaN thermal conductivity, there is not a significant dependence of doping density for intentional doping levels between 1016cm-3 and 1018cm-3.


“We are enjoying incremental improvement in our bulk GaN materials properties, which is being born out in their thermal conductivity, as well as in other properties,” stated Kyma CTO


Ed Preble. Preble added, “We are also pleased to learn from Professor Muth’s research group that our polycrystalline GaN is also a pretty good thermal conductor.


In retrospect this is not extremely surprising: The grains are relatively large (10 to 40 microns) and relatively low in extended defect density, plus the material density is close to its theoretical value, and the chemical purity level is 6N’s (less than 1 part per million in impurities by weight) or better.”


Kyma’s polycrystalline GaN is available in customer defined shapes, ranging from 1cm wide cubes to round wafers with diameters of 1-inch, 2-inch, 3-inch and 100mm and thicknesses between 0.5 and 5 mm. The round form factor can be polished to an optically flat level.


8 www.compoundsemiconductor.net October 2011


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