Transfer of vertically aligned silicon nanowires array using sacrificial porous silicon layer

Abstract

Metal-assisted chemical etching (MACE) fabricates silicon nanowires (SiNWs) array at room temperature on the crystalline Si substrate. The SiNWs, however, need to be transferred to a better substrate for additional flexibility, lesser cost, and transparency compared to Si substrate resulting in improved device functionality. The paper explores, optimizes, and compares two techniques to transfer SiNWs to glass: gluing technique, and two-step electro-assisted technique. The objective is to preserve the length of nanowires on a larger transfer area. Gluing technique spin-coats an adhesive layer of polyvinyl acetate (PVAc) and methanol solution. The gluing method studies the effect of variation in MACE time on the percentage transfer ratio for the optimized PVAc layer. The electro-assisted technique detaches the vertically aligned SiNWs array with the aid of a sacrificial porous Si layer for variation in anodization time. A yield of the gluing and electro-assisted technique is optimized for MACE and anodization time. The transferred layer is characterized by various parameters, such as the percentage transferred length (%TRL), total transfer area, crystallinity, strain, and morphology of the SiNWs. For optimized values, the gluing method achieved%TRL = 68.2% while transferring 0.95 cm2 of the film area, whereas the electro-assisted technique achieves%TRL= 7.4 for an area of 19 cm2.