Study of Photo-Oxidized n-Type Textured Silicon Surface through Electrochemical Impedance Spectroscopy

Abstract

For crystalline silicon (c-Si) solar cells, it is useful to measure accurately the thickness of silicon oxide (SiO x) layer presents on textured c-Si surface to further adapt the fluoride-based etching treatment. Common techniques used to characterize thin films thicknesses, such as ellipsometry or profilometry, are however not suitable for highly textured surfaces. In this work, a methodology based on Electrochemical Impedance Spectroscopy (EIS) has been developed to determine the thickness of anodic SiO x on n-type textured c-Si surface. EIS measurements have been carried out on bare c-Si surface as well as on c-Si surface with various anodic SiO x thicknesses grown by photo-oxidation. The as-obtained Nyquist and Bode diagrams enabled to plot the related Mott-Schottky curves and determine the corresponding flatband potentials (V fb). A reference standard graph giving the anodic SiO x thickness according to measured V fb has been therefore established. A shift of Mott-Schottky curves towards higher potential values with increased anodic SiO x thickness has been shown and explained. Mott-Schottky curves of photo-oxidized silicon surfaces have demonstrated a particular shape related to the different behaviors of Si/SiO x /electrolyte device depending on the applied overpotential. These results have been used to study the etching rate of anodic SiO x in NaHF 2 fluoride media.