What is the thermal conductivity of gallium nitride (GaN)?

Thermal conductivity (TC) is a measure of the ability of a material to conduct heat and it is expressed in units of energy per unit distance per unit temperature. For non-metallic crystalline materials including gallium nitride (GaN), heat is conducted mostly through lattice vibrations (phonons). Therefore, the thermal conductivity can be reduced by anything that affects phonon physics, which includes dislocations and other extended defects, intrinsic point defects such as vacancies and antisites, and extrinsic defects (impurities). And because phonon activity is temperature dependent, TC varies with temperature as well.

For these reasons, room temperature TC of GaN varies from ~100 W/m·K for highly defective GaN epilayers grown on Si and sapphire to 165 W/m·K for Kyma's polycrystalline GaN to 260 W/m·K for Kyma's bulk GaN.

In 2011 Kyma published a press release discussing the TC of their GaN materials - see http://www.kymatech.com/news/144-kyma-discusses-the-thermal-conductivity-of-their-gallium-nitride-materials.