Role of Ag-catalyst morphology and molarity of AgNO₃ on the size control of Si nanowires produced by metal-assisted chemical etching

Abstract

In this paper we demonstrate a controlled fabrication of vertically aligned silicon nanowires (Si NWs) on n-type (100)-oriented and p-type (111)-oriented Si wafers by metal-assisted chemical etching (MaCE) method. The etching of Si-wafer samples covered with Ag nanoparticles as catalyst agents was carried out in HF/H₂O₂/H₂O solution of various volumetric ratios. We show that molar concentration of AgNO₃, Ag-nanoparticles deposition time, and the etching time determine the shape and size of produced Si NWs. Vertically aligned tall Si NWs can be produced by immersing the n-Si(100) wafer with pre-deposited from AgNO₃ [22mM]/HF [5M]-solution silver nanoparticles in the etchant HF/H₂O₂/H₂O (4:1:4) for different time. When the duration of Ag-deposition increased from 15 to 30 s in a solution 22 mM AgNO₃/5 M HF, the etching rate of Ag-loaded n-Si(100) samples was found to be the same (∼ 1.6 µm/min). For 120 s Ag-deposited samples, the etching rate decreased to 560 nm/min. So, the height and density of Si NWs can be accurately controlled by varying the etching time as the vertical etching rate remained constant for 15 and 30 s Ag-deposited samples. Also we show that in case of p-Si(111), highly structured array of Si NWs can be produced only after a 30 min etching of the p-Si(111) wafer covered with Ag deposited from AgNO₃ [22mM]/HF [5M]-solution in an etchant HF/H₂O₂/H₂O (4:1:8).

Key Words:

• nanowires
• silicon
• metal-assisted chemical etching
• size control
• Ag nanoparticles