Application of nickel for fabrication of nanoporous silicon and light induced electroless nickel metallization for silicon diode

Abstract

Fabrication of nano textured silicon through metal-assisted chemical etching (MACE) technique has attracted attention as a simple, low-cost and versatile technique for producing antireflective silicon layer. In this study, a novel single-step nickel assisted etching technique was applied to fabricate an antireflective, nonporous mono c-Si (black Si) in an aqueous solution containing hydrofluoric acid (HF), hydrogen peroxide (H2O2) and NiSO4 at 40oC. Field emission scanning electron microscope was used to characterize different morphologies of the textured Si. Optical reflection measurements of samples were carried out to compare the reflectivity of different morphologies. Results indicated that vertical as well as horizontal pores with nanosized diameters were bored in the Si wafer after 1hour treatment in the wet electroless etching solution containing different molar ratios of H2O2 to HF. Increasing H2O2 concentration in electrochemical etching solution had a considerable influence on the morphology of textured Si due to higher injection of positive charges from nickel atoms onto the silicon surface. Optimized concentration of H2O2 led to formation of an nanoporous antireflective Si layer with 2.1% reflectance of incident light.

Result indicated that further increase in molar ratio of H2O2 to HF led to formation of a cobblestone structure of silicon which dramatically enhance the reflection of incident light. nickel assisted etching technique also was applied for producing an antireflective nano-scale porous structures on multi-crystalline silicon wafer. It was observed that nanotextured multi c-Si fabricated through optimized ration of oxidation agent to HF exhibited lower reflection than standard isotropic texturing using a standard acid solution. As a final step, the optimized texturing process was applied to fabricate multi c-si solar cell devices showing promising results regarding cell performance parameters.

In the second part of my study, Light Induced Electroless Plating technique was applied to deposit Ni seed layer on the n-side of a silicon diode structure. Morphology of the nickel seed layer and phase characterization of nickel silicide at different bath conditions and annealing temperatures was examined through scanning electron microscopy, X-ray diffractometer and Raman spectroscopy respectively. Moreover, transmission line measurement (TLM) technique was employed to determine the contact resistance of Ni/Si stack after thermal treatment and to understand its correlation with the chemical-structural properties. Results indicated that low electrical resistive mono-silicide (NiSi) phase as low as 5 mΩ.cm2 was obtained in temperature range of 450oC to 500oC.