Abstract
Silicon nanowires (SiNWs) were fabricated by metal-assisted chemical etching (MACE) where hydrofluoric acid (HF), which is typically used in this method, was changed into ammonium fluoride (NH4F). The structure and optical properties of the obtained SiNWs were investigated in details. The length of the SiNW arrays is about 2 μm for 5 min of etching, and the mean diameter of the SiNWs is between 50 and 200 nm. The formed SiNWs demonstrate a strong decrease of the total reflectance near 5–15 % in the spectral region λ < 1 μm in comparison to crystalline silicon (c-Si) substrate. The interband photoluminescence (PL) and Raman scattering intensities increase strongly for SiNWs in comparison with the corresponding values of the c-Si substrate. These effects can be interpreted as an increase of the excitation intensity of SiNWs due to the strong light scattering and the partial light localization in an inhomogeneous optical medium. Along with the interband PL was also detected the PL of SiNWs in the spectral region of 500–1100 nm with a maximum at 750 nm, which can be explained by the radiative recombination of excitons in small Si nanocrystals at nanowire sidewalls in terms of a quantum confinement model. So SiNWs, which are fabricated by environment-friendly chemistry, have a great potential for use in photovoltaic and photonics applications.
Highlights
In the last years, silicon nanowires (SiNWs) are of great interest because of their potential applications in microand optoelectronics [1, 2], photonics [3], photovoltaics [4, 5], and sensorics [6,7,8]
An alternative method was metal-assisted chemical etching (MACE) by which initially it was believed that the porous silicon (PSi) was obtained [10, 11]
MACE is based on the anisotropic etching of crystalline silicon (c-Si) in aqueous solutions which are usually based on hydrofluoric acid (HF) [10,11,12,13,14,15]
Summary
Silicon nanowires (SiNWs) are of great interest because of their potential applications in microand optoelectronics [1, 2], photonics [3], photovoltaics [4, 5], and sensorics [6,7,8]. SiNWs were obtained by vapor-liquid-solid method with the help of a noble metal (mostly gold, Au) which was first proposed by Wagner and Ellis in 1964 [9]. An alternative method was metal-assisted chemical etching (MACE) by which initially it was believed that the porous silicon (PSi) was obtained [10, 11]. It has been shown that the SiO2 etch rate in aqueous NH4F solutions depends on the pH and on the NH4F concentration [26]. Aqueous NH4F solution was proposed as an alternative of HF in the electrochemical method of obtaining PSi films [27,28,29]. The microstructure properties of the fabricated PSi have shown a strong dependency from the pH of the electrolyte
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