Raman diagnostics of photoinduced heating of silicon nanowires prepared by metal-assisted chemical etching

Abstract

Raman spectroscopy was applied to investigate laser-induced heating of silicon nanowires (SiNWs) formed by metal-assisted chemical etching of lightly boron-doped crystalline silicon (c-Si) wafers. Low-frequency shift of the Raman peak from 520.5 cm−1 to about 517 cm−1 for SiNWs with length of 40–65 µm under laser irradiation with wavelengths of 632.8 or 488 nm was observed, and it was explained by an increase in the average temperature of SiNWs on about 150 K for the laser intensity about 1 kW/cm2. The same photoinduced heating was confirmed by analyzing the ratio between the Stokes and anti-Stokes components of the Raman scattering. The obtained experimental data allow us to estimate the thermal conductivity coefficient of SiNW array ~0.1 W/(m K), which is three orders of magnitude smaller than that of c-Si. Furthermore, the Raman spectra of SiNWs under excitation with intensity above 0.2–0.5 kW/cm2 consisted of an additional low-frequency peak, which is related to an overheated subsystem of well spatially separated fine SiNWs up to 600–700 K. The observed strong photoinduced heating can be used for local laser-induced treatment of SiNWs and biomedical applications.