Thermal conductivity of fully and partially coalesced lateral epitaxial overgrown GaN/sapphire (0001) by scanning thermal microscopy

We have measured high spatial/depth resolution (∼2–3 μm) thermal conductivity (κ) at 300 K of both fully and partially coalesced GaN/sapphire (0001) samples fabricated by lateral epitaxial overgrowth. On the fully coalesced sample we found $\text{1.86}\mathrm{W/cm K}\text{<κ<2.05\hspace{0.05em}}\mathrm{W/cm K}$ over a distance of approximately 50 μm. One of the partially coalesced samples had $\text{2.00\hspace{0.05em}}\mathrm{W/cm K}\text{<κ<2.10\hspace{0.05em}}\mathrm{W/cm K}$ on the overgrown regions, as identified by atomic force microscopy imaging. These latter results are the highest thermal conductivity values reported on GaN material. A correlation between low threading dislocation density and high thermal conductivity values was established.