Optical and Electrical Characteristics of Silicon Nanowires Prepared by Electroless Etching

Abstract

Silicon nanowires (SiNWs) were fabricated by the electroless etching of an n-type Si (100) wafer in HF/AgNO₃. Vertically aligned and high-density SiNWs are formed on the Si substrates. Various shapes of SiNWs are observed, including round, rectangular, and triangular. The recorded maximum reflectance of the SiNWs is approximately 19.2%, which is much lower than that of the Si substrate (65.1%). The minimum reflectance of the SiNWs is approximately 3.5% in the near UV region and 9.8% in the visible to near IR regions. The calculated band gap energy of the SiNWs is found to be slightly higher than that of the Si substrate. The I-V characteristics of a freestanding SiNW show a linear ohmic behavior for a forward bias up to 2.0 V. The average resistivity of a SiNW is approximately 33.94 Ω cm.

Keywords: Band gap energy; Electroless etching; Microstructures; Reflectance; Resistivity; Silicon nanowires.

Fig. 1

SEM images of a the pre-cleaned Si wafer and b the Si wafer etched in 5 M HF without AgNO₃ solution

Fig. 2

SEM image showing the formation of SiNWs with silver dendrites after the electroless etching process (before aqua regia cleaning)

Fig. 3

SEM images of SiNW arrays fabricated via the electroless etching method: a 45° view, b, c top view, d cross-section/side view

Fig. 4

EDX analysis results of SiNW arrays after the etching processes: a before aqua regia cleaning (88.96 at.% Si and 11.04 at.% Ag) and b after aqua regia cleaning (100.00 at.% Si and 0.00 at.% Ag)

Fig. 5

TEM images of loose SiNWs: a bundle of SiNWs with various sizes and shapes, b round-shaped SiNW, c rectangular-shaped SiNW, and d triangular-shaped SiNW

Fig. 6

Reflectance (R) versus wavelength (λ) for a Si substrate and the SiNW arrays

Fig. 7

Plot of (F(R)*hν)^1/2 versus photon energy (hν) for a Si substrate and the SiNW arrays

Fig. 8

Schematic diagram of the experimental setup for the electrical measurement by AFM

Fig. 9

SEM and AFM images of the vertically aligned SiNWs. A triangle-shaped wire was chosen for the electrical measurement by AFM

Fig. 10

I–V curves of an individual freestanding SiNW measured by AFM. The characteristics correspond to resistor behavior. The inset shows the AFM scanning area and AFM probe positions for the electrical measurement