The morphology of silicon nanowire samples: A Raman study

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.