Quantitative heat dissipation characteristics in current-carrying GaN nanowires probed by combining scanning thermal microscopy and spatially resolved Raman spectroscopy.

Using an approach combining scanning thermal microscopy (SThM) and spatially revolved Raman spectroscopy, we have investigated quantitatively the heat dissipation characteristics in substrate-supported and suspended (with asymmetric type of contacts) current-carrying GaN nanowires with diameters of ∼40-60 nm, where the phonon confinement is expected to play an important role in thermal transport. In particular, this approach allows direct measurements of nanowire-substrate/electrode interface thermal resistances and the nanowire thermal conductivity. On the basis of these results, the nanowire-substrate thermal transfer was suggested to be the main heat dissipation route, counting for ∼80-93% of the total dissipated heat, whereas the nanowire-electrode interface plays a minor role. The relative significance of nanowire-substrate/electrode interfaces in dissipating heat was further demonstrated in suspended nanowire devices. The measured nanowire thermal conductivity (∼40-60 W/mK) is lower than that in bulk GaN, possibly due to the phonon confinement and boundary scattering effects. Besides providing quantitative insight into heat dissipation characteristics, our results also reveal aspects, particularly the topography-related thermal signals and the relative significance of various tip-sample thermal transfer processes, that are important to advancing the applications of SThM technique in nanoscale thermal characterizations.