15 September 2011

Kyma reports thermal conductivity analysis on GaN materials

Kyma Technologies Inc of Raleigh, NC, USA, which provides crystalline gallium nitride (GaN), aluminum nitride (AlN) and aluminum gallium nitride (AlGaN) materials and related products and services, has announced the results of an analysis of the thermal conductivity of several of its GaN materials products, 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 many of the results during this three-year period for bulk and template single-crystal GaN materials. More recently it also measured the thermal conductivity of Kyma’s high-purity polycrystalline GaN. The results include two record numbers:

• bulk GaN has been measured to have thermal conductivities of 260±5W/mK;
  
• high-purity polycrystalline GaN has been measured to have thermal conductivities of 165±5W/mK.

Additionally, the thermal conductivity of Kyma’s GaN-on-sapphire templates is found to vary from 180W/mK to 220W/mK for thicknesses between 100 microns and 400 microns, respectively (a result of declining dislocation density from about 8x108cm–2 to 3x107cm–2, respectively). Kyma’s more typical GaN template product has 5 microns of GaN and was not measured but is expected, based on NCSU’s analysis of the literature, to have a thermal conductivity of about 130W/mK (~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 no significant dependence on doping density for intentional doping levels between 1016cm–3 and 1018cm–3, says Kyma.

“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,” says chief technology officer Dr Ed Preble. “Our polycrystalline GaN is also a pretty good thermal conductor," he adds. "This is not extremely surprising:  the grains are relatively large (10–40 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 of 0.5–5mm. The round form factor can be polished to an optically flat level, the firm adds.

Tags: Kyma GaN

Visit: www.kymatech.com