Removal of Ag remanence and improvement in structural attributes of silicon nanowires array via sintering

Paresh Kale,Mihir Kumar Sahoo

doi:10.1038/s41598-021-03654-5

Abstract

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost. The remanence of metal, i.e., silver nanoparticles (AgNPs) used in the MACE, deteriorates the device (especially solar cell) performance by acting as a defect center. The superhydrophobic behavior of nanowires (NWs) array prohibits any liquid-based solution (i.e., thorough cleaning with HNO3 solution) from removing the AgNPs. Thermal treatment of NWs is an alternative approach to reduce the Ag remanence. Sintering temperature variation is chosen between the melting temperature of bulk-Ag (962 °C) and bulk-Si (1412 °C) to reduce the Ag particles and improve the crystallinity of the NWs. The melting point of NWs decreases due to surface melting that restricts the sintering temperature to 1200 °C. The minimum sintering temperature is set to 1000 °C to eradicate the Ag remanence. The SEM–EDS analysis is carried out to quantify the reduction in Ag remanence in the sintered NWs array. The XRD analysis is performed to study the oxides (SiO and Ag2O) formed in the NWs array due to the trace oxygen level in the furnace. The TG-DSC characterization is carried out to know the critical sintering temperature at which remanence of AgNPs removes without forming any oxides. The Raman analysis is studied to determine the crystallinity, strain, and size of Si nanocrystals (SiNCs) formed on the NWs surface due to sidewalls etching. An optimized polynomial equation is derived to find the SiNCs size for various sintering temperatures.

Highlights

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost
X‐ray diffraction (XRD) analysis helps in determining the presence of AgNPs in the NWs array
Since the Ag particles oxidize quickly under atmospheric c onditions[24], at the higher sintering temperature, Ag2O (220) and Ag2O (222) planes are formed (Fig. 3), which remains for all the sintered samples at 54.5°, 69.3° respectively

Summary

Introduction

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost. A popular method, metal-assisted chemical etching (MACE), used for synthesizing SiNWs, fabricates a large surface area and higher aspect ratio of SiNWs array at low temperature and relatively low cost[16,17,18,19]. The superhydrophobic surface of the SiNWs array disallows a liquid-based solution to remove the remanence of metal particles present at the substrate and NWs interface. I.e., heat treatment of SiNWs array above the melting point of the metal catalysts removes the metal particles from the NWs array without melting the NWs. The decreasing order of melting temperature of metal catalysts used in HF-containing solution is Pt (1768 °C), Cu (1084 °C), Au (1064 °C), and Ag (962 °C). Though the melting point of AgNPs is much lesser than the bulk-Ag, a minimum sintering temperature of 1000 °C is chosen to remove the Ag remanence from the NWs array altogether. The sintering temperature is varied from 1000 to 1200 °C to remove the Ag remanence from the SiNWs array

Objectives

Methods

Results

Discussion

Conclusion