We explore the combined effects of phonon confinement and local heating caused by laser beam absorption on the Raman spectra of Germanium nanowires of different diameters ($6\mathrm{nm}$, $7\mathrm{nm}$, and $12\mathrm{nm}$). The asymmetric broadening and downshifting of the first order Raman band is studied as a function of the average wire diameter and the local temperature of the nanowires. The basic phenomenological model with a modified confinement function incorporated with thermal effects is in good agreement with our experimental results. We also show the effects of the nanowire diameter, thermal conductivity of the underlying substrate, and the mediating substance (gallium in this case) on the local temperature of the nanowires.

• Received 19 April 2006

DOI:https://doi.org/10.1103/PhysRevB.74.155421