The effect of differently sized Ag catalysts on the fabrication of a silicon nanowire array using Ag-assisted electroless etching

Abstract

A simple and low cost method to generate single-crystalline, well-aligned silicon nanowires (SiNWs) of large area, using Ag-assisted electroless etching, is presented and the effect of differently sized Ag catalysts on the fabrication of SiNWs arrays is investigated. The experimental results show that the size of the Ag catalysts can be controlled by adjusting the pre-deposition time in the AgNO3/HF solution. The optimum pre-deposition time for the fabrication of a SiNWs array is 3 min (about 162.04 +/- 38.53 nm Ag catalyst size). Ag catalysts with smaller sizes were formed in a shorter pre-deposition time (0.5 min), which induced the formation of silicon holes. In contrast, a large amount of Ag dendrites were formed on the silicon substrate, after a longer pre-deposition time (4 min). The existence of these Ag dendrites is disadvantageous to the fabrication of SiNWs. Therefore, a proper pre-deposition time for the Ag catalyst is beneficial to the formation of SiNWs. SiNWs were synthesized in the H2O2/HF solution system for different periods of time, using Ag-assisted electroless etching (pre-deposition of the Ag catalyst for 3 min). The length of the SiNWs increases linearly with immersion time. From TEM, SAED and HRTEM analysis, the axial orientation of the SiNWs is identified to be along the [001] direction, which is the same as that of the initial Si wafer. The use of HF may induce Si-H-x bonds onto the SiNWarray surface. Overall, the Ag-assisted electroless etching technique has advantages, such as low temperature, operation without the need for high energy and the lack of a need for catalysts or dopants. (C) 2012 Elsevier B.V. All rights reserved.