Abstract
Porous silicon (PS) can be used as a loading template in sensing or as a matrix to develop nanoparticle arrays. We present a comprehensive study of PS morphology and optical properties before and after the pore opening process, including the determination of thickness, pore size, and pore density of PS layers, its surface wettability, and reflectivity. The PS samples were fabricated by electrochemical anodization of monocrystalline silicon wafer in 5–20 wt.% hydrofluoric acid (HF) solution at a current density in the range of 20–200 mA/cm2. Anodization was followed by the pore opening process, i.e., the removal of a parasitic superficial layer with a “bottleneck” structure by reactive ion etching (RIE). The results illustrate that “bottleneck”-free PS allows to achieve a high pore density using a low HF concentration and a reduced current density. We established that this structure demonstrates higher hydrophobicity in comparison to the samples before RIE. The applicability of the developed “bottleneck”-free PS was tested via filling the pores with silver nanoparticles, indicating its potential use as a template for the fabrication of nanoparticle arrays.
Highlights
Accepted: 8 June 2021Porous silicon (PS) represents an intriguing platform to engineer miniature sensors compatible with Si technology that provide accurate and reliable detection of various organic molecules in a liquid or gaseous environment
We demonstrated that reactive ion etching (RIE) is an efficient method for the removal of the parasitic surface layer without damaging the morphology of the PS
Changing the current density and hydrofluoric acid (HF) concentration during the electrochemical etching process enables the pore size to be managed in a range from 10 nm up to 160 nm
Summary
Accepted: 8 June 2021Porous silicon (PS) represents an intriguing platform to engineer miniature sensors compatible with Si technology that provide accurate and reliable detection of various organic molecules in a liquid or gaseous environment. The anodization of silicon wafers is usually accompanied by the growth of a thin parasitic layer caused by surface defects (e.g., surface roughness or uneven distribution of doping atoms) on the initial monocrystalline substrate. This surface layer usually consists of pores with a lower diameter compared to the pores distributed in the deeper layer, resulting in the so-called “bottleneck” effect. It can strongly affect the morphology, mechanical, and electrical properties of the final PS-based device [3]. Mesoporous silicon is a suitable material for sensing elements because the pore diameters are equal or
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