Photoacoustic characterization of nanowire arrays formed by metal-assisted chemical etching of crystalline silicon substrates with different doping level

Silicon nanowire (SiNW) arrays were investigated by gas-microphone photoacoustic (PA) technique to evaluate the thermal conductivity and optical absorption. The arrays with SiNW's length from 3 to 25 mu m were formed by metal-assisted chemical etching of (100)-oriented monocrystalline silicon (c-Si) substrates with the low and high concentration of doping impurities. PA responses of SiNWs were excited by sources with wavelengths of 460 and 630 nm in the frequency range from 15 to 1150 Hz. An analysis of the experimental data reveals that the thermal conductivities of SiNWs formed on the lightly and heavily doped substrates are about 4-7 and 0.17-0.22 W/(mK), respectively. The latter value is explained by the porous structure of the SiNWs, promoting a strong restriction of the phonon free path. The thermal conductivity and optical absorption of SiNW arrays depend on the doping level and length of SiNWs due to a combination of the phonon and light scattering processes.