Raman spectra of silicon nanowires (SiNWs) are studied as a function of laser excitation power and temperature. With increase in temperature and power a red-shift of the SiNWs first order optical mode is observed. At ambient conditions, the Raman shift shows a saturated behavior beyond a critical power. Similar measurements, under vacuum, rule out effects due to thermal convection as a reason for the observed saturation. We assign this to a change in sample morphology. A simulation of the SiNW peak position reveals that its temperature behavior can be explained by a four-phonon anharmonic process. SEM image of a typical SiNWs sample. The SiNW are 15 nm in diameter and up to a few microns long. The sample is a large bundle of SiNWs (up to 50mm thick) with strong porosity.
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