The impact of film thickness and substrate surface roughness on the thermal resistance of aluminum nitride nucleation layers

Thickness dependent thermal conductivity measurements were made on aluminum nitride (AlN)thin films grown by two methods on the (0001) surfaces of silicon carbide (SiC) and sapphiresubstrates with differing surface roughness. We find that the AlN itself makes a small contribution to the overall thermal resistance. Instead, the thermal boundary resistance (TBR) of 5.1 ± 2.8 m2K/GW between the AlN and substrate is equivalent to 240 nm of highly dislocatedAlN or 1450 nm of single crystal AlN. An order-of-magnitude larger TBR was measured betweenAlN films and SiC substrates with increased surface roughness (1.2 nm vs. 0.2 nm RMS). Atomic resolution TEM images reveal near-interface planar defects in the AlN films grown on the roughSiC that we hypothesize are the source of increased TBR.