Structure, morphology, and photoluminescence of porous Si nanowires: effect of different chemical treatments

Ioannis Leontis,Andreas Othonos,Androula G Nassiopoulou

doi:10.1186/1556-276x-8-383

Abstract

The structure and light-emitting properties of Si nanowires (SiNWs) fabricated by a single-step metal-assisted chemical etching (MACE) process on highly boron-doped Si were investigated after different chemical treatments. The Si nanowires that result from the etching of a highly doped p-type Si wafer by MACE are fully porous, and as a result, they show intense photoluminescence (PL) at room temperature, the characteristics of which depend on the surface passivation of the Si nanocrystals composing the nanowires. SiNWs with a hydrogen-terminated nanostructured surface resulting from a chemical treatment with a hydrofluoric acid (HF) solution show red PL, the maximum of which is blueshifted when the samples are further chemically oxidized in a piranha solution. This blueshift of PL is attributed to localized states at the Si/SiO2 interface at the shell of Si nanocrystals composing the porous SiNWs, which induce an important pinning of the electronic bandgap of the Si material and are involved in the recombination mechanism. After a sequence of HF/piranha/HF treatment, the SiNWs are almost fully dissolved in the chemical solution, which is indicative of their fully porous structure, verified also by transmission electron microscopy investigations. It was also found that a continuous porous Si layer is formed underneath the SiNWs during the MACE process, the thickness of which increases with the increase of etching time. This supports the idea that porous Si formation precedes nanowire formation. The origin of this effect is the increased etching rate at sites with high dopant concentration in the highly doped Si material.

Highlights

Si nanowires (SiNWs) are interesting building blocks of different nanoelectronic devices [1,2,3], solar cells [4,5], and sensors [6]
We investigated the structure, morphology, and photoluminescence from SiNWs fabricated by a single-step metal-assisted chemical etching (MACE) process on highly doped p-type (100) Si wafers with a resistivity of approximately 0.005 Ω·cm and the effect of different surface chemical treatments on the above
We used scanning and transmission electron microscopy to demonstrate that the obtained nanowires were fully porous, and this result was further supported by the fact that they were fully dissolved in an hydrofluoric acid (HF) solution after successive HF and piranha treatments

Summary

Introduction

Si nanowires (SiNWs) are interesting building blocks of different nanoelectronic devices [1,2,3], solar cells [4,5], and sensors [6]. There are different techniques to fabricate vertical SiNWs on a silicon wafer, which include bottom-up methods using catalysts to initiate nanowire growth [7] and top-down methods using either advanced lithographic techniques, combined with anisotropic etching [8], or chemical etching catalyzed by metals (metal-assisted chemical etching (MACE) method) [9,10]. This last method is a simple low-cost method that permits to obtain vertical Si nanowires on the Si wafer with length that can exceed several tens of micrometers. The chemical composition of the surface of the Si nanostructures composing the porous Si nanowires was investigated after each chemical treatment and correlated with their photoluminescence properties

Methods

Results

Discussion

Conclusion