Facile morphology control of high aspect ratio patterned Si nanowires by metal-assisted chemical etching

Facile and effective method to fabricate highly ordered silicon nanowires (SiNWs) using metal-assisted chemical etching (MACE) was demonstrated. MACE solutions with various concentrations were studied to understand the etching mechanism for patterned Si substrates with different doping concentrations. MACE rate of Si (100) at different time periods was studied with different doping concentrations (p, p+, n, and n+) at a MACE solution concentration of 5:1:1 for an accurate morphology control and reproducibility of the SiNWs. Based on a four-step model, the SiNW formation mechanism was proposed involving anisotropic etching of SiNWs based on hole transfer between Au/Si interfaces exposed when subjected to MACE solution. Time dependent variation in etch rate of Si to fabricate SiNWs was observed with different doping concentration. The effect of the doping concentration on the etching was revealed based on band diagrams. However, agglomeration of p+-SiNWs was observed, which was attributed to their doping and ability to act against various forces like surface tension during drying. Different aspect ratios of SiNWs were observed for different time periods; n+-SiNWs exhibited the maximum aspect ratio of approximately 81. A visible-light absorbance analysis revealed the potential of the synthesized SiNWs can be good base and host materials for various light harvesting and energy storage devices.