Optical Diagnostics of Free Charge Carriers in Silicon Nanowire Arrays

Abstract

The impact of free charge carriers in arrays of silicon nanowires (SiNWs) of p‐ and n‐type conductivities on their optical properties is probed by means of the infrared spectroscopy in attenuated total reflectance mode (IR‐ATR) and Raman scattering. SiNWs are fabricated by metal‐assisted chemical etching of low‐doped p‐type crystalline silicon (c‐Si) wafers followed by thermodiffusional doping with p‐ and n‐type impurities. The free charge carrier concentration in SiNWs is determined from their ATR spectra fitted using a model of the anisotropic effective medium with free charge carriers. The obtained data on the free charge carrier concentrations in the range of 1019–1020 cm−3 are compared with the corresponding values obtained from the Raman spectra, which are analyzed by considering the Fano effect in SiNWs, and the results of both methods are used to evaluate the electrical properties of SiNWs. The proposed optical methods to probe the electrical properties of SiNWs are discussed in view of possible applications in nanoelectronics and thermoelectric devices.