Nanostructured surfaces

Role of Ag-catalyst morphology and molarity of AgNO3 on the size control of Si nanowires produced by metal-assisted chemical etching
O.Y. Ostapiv, S.I. Nichkalo, A.A. Druzhinin

Department of Semiconductor Electronics, Lviv Polytechnic National University, 
S. Bandera Str., 12, Lviv-79013, Ukraine
E-mail: oleksandr008@gmail.com

One-dimensional Si nanowires (SiNWs) have aroused much interest owing to their importance in fundamental research and potential applications in nanotechnology. Controllable fabrication of SiNWs is therefore a prerequisite for various applications. In this regard, the metal-assisted chemical etching (MaCE) is a simple, cost-effective, and powerful etching technique that is capable of producing high aspect ratio semiconductor nanostructures applicable in various fields. 
In this research work we demonstrate controlled fabrication of vertically aligned SiNWs on n-Si(100) and p-Si(111) wafers by 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 determines the shape and size of produced SiNWs. Also, we established that the size of Ag catalyst affects the morphology of the etched SiNWs. For instance, the 22 mM-molar concentration of an initial AgNO3 enabled to produce vertically aligned regular SiNWs etched from Si wafers in HF/H2O2/H2O solution (4:1:4) at different time (Fig. 1). From Fig. 1, it is observed that, as the etching time increases from 1 to 5 min, there is increase in SiNWs height from 1 to 2,5 µm. At the same time, the diameter of the SiNWs was found to be 150–300 nm.
                                  
                           a                                                                             b
Fig. 1. Cross-section SEM images of SiNWs prepared by MaCE method on n-type Si(100) wafer in HF/H2O2/H2O solution (4:1:4) at different etching time: (a) 1 min; (b) 5 min