Kyma Discusses the Thermal Conductivity of their Gallium Nitride Materials

Kyma Technologies, Inc., a leading supplier of crystalline aluminum nitride (AlN) and gallium nitride (GaN) and related products and services, announced today the results of an analysis of the thermal conductivity of several of Kyma’s GaN materials products.

The thermal conductivity analysis was carried out over the past three years by researchers in the group led by Professor John Muth of the Materials Science and Engineering Department of North Carolina State University (NCSU).  Muth’s group has published (see References below) 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.

The results include two record numbers:

1)  Kyma’s bulk GaN has been measured to have thermal conductivities in the range of 260 ± 5 W/mK

2)  Kyma’s 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 on sapphire 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 is ~20% 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.

Dr. 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 (<1PPM 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”, 2”, 3” and 100mm and thicknesses between 0.5 and 5 mm.  The round form factor can be polished to an optically flat level.

For more information about Kyma’s products, visit its webpage at


1.  C. Mion, J. F. Muth, E. A. Preble, and D. Hanser, "Accurate dependence of gallium nitride thermal conductivity on dislocation density," Appl. Phys. Lett. 89, 092123 (2006).

2.  C. Mion, “Investigation of the thermal properties of gallium nitride using the three omega technique,” PhD Dissertation, 2006,

About Kyma Technologies:

Kyma is a leading supplier of crystalline nitride semiconductor materials including gallium nitride (GaN), aluminum nitride (AlN), and aluminum gallium nitride (AlGaN) and related products and services.

The market for nitride semiconductor devices was $12B in 2010 and is expected to reach $90B over the long term, including $60B in visible lighting applications and $30B in power electronics applications.

Kyma’s materials products enable higher electrical efficiency in all of their customers’ applications, in support of a greener tomorrow.

For more information about Kyma Technologies, visit, e-mail, or call the company directly at 919.789.8880.

Kyma is a registered trademark of Kyma Technologies, Inc.