Effective Removal of Surface Recombination Centers in Silicon Nanowires Fabricated by Metal-Assisted Chemical Etching

High-density silicon nanowires (SiNWs) were fabricated on p-Si substrates by metal-assisted chemical etching (MACE). A chemical cleaning with HF/piranha/HF was used to remove structural defects from the nanowire surface which are at the origin of surface recombination states. Surface photovoltage (SPV) spectroscopy, capacitance-voltage (C-V), and conductance measurements were used to study the SiNW properties and assess the effectiveness of the cleaning process. For the as-grown samples, the analysis of the SPV amplitude and phase spectra demonstrated high density of positively charged surface recombination centers. These centers increase the surface band bending and decrease the minority carrier lifetime and diffusion length. Si nanostructures at the SiNW surface introduce slow traps, as evidenced by the frequency dispersion at accumulation of the C-V curves and the increase of the diffusion length with frequency. All these features are effectively reduced when the SiNWs are subjected to HF/piranha/HF chemical cleaning. Thus, a cheap and effective way is demonstrated to reduce the surface state density and improve the electronic quality of the surface of SiNWs.