Doping effects on the Raman spectra of silicon nanowires

Un-doped, $N$-type, and $P$-type doped silicon nanowires (SiNWs) were grown at $460\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $25\phantom{\rule{0.3em}{0ex}}\text{Torr}$ via the vapor-liquid-solid (VLS) mechanism. The intensity ratio of anti-Stokes/Stokes $({I}_{\mathrm{AS}}∕{I}_{\mathrm{S}})$ peaks is used as an index of the sample temperature. Different SiNWs exhibit different Raman frequency shifts because their compressive stresses due to heating differ. The slopes of the ${I}_{\mathrm{AS}}∕{I}_{\mathrm{S}}$ peak ratio versus the Raman frequency for boron-doped, un-doped, phosphorous-doped SiNWs, and bulk Si are $\ensuremath{-}0.078$, $\ensuremath{-}0.036$, $\ensuremath{-}0.035$ and $\ensuremath{-}0.02\phantom{\rule{0.3em}{0ex}}\text{per}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, respectively. The different slopes reveal the different heating-induced compressive stresses in the SiNWs with different dopants and bulk Si.