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

We have measured high spatial/depth resolution (similar to 2-3 mu m) thermal conductivity (kappa) 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 1.86W/cm K < kappa < 2.05 W/cm K over a distance of approximately 50 mu m. One of the partially coalesced samples had 2.00 W/cm K < kappa < 2.10 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. (C) 2000 American Institute of Physics. [S0003-6951(00)04336-9].