Anodic current transient for n-Si|SiO2 electrodes in HF solution: the relationship between the current and the interface structure

The anodic current transient for n-Si|SiO2 electrodes is investigated in HF solution in the dark. Usually, the anodic current shows a sharp peak, and the charge QD is determined by integrating the current transient. The charge QD becomes large when measured in solutions with a high pH value or with a low HF concentration, due to successive dissolution of some Si monolayers before the surface is stabilized by hydrogen termination. Such situation can be avoided if an HF solution of high concentration and low pH (e.g., 1 M HF of pH 1) is used, in which HF molecules are the dissolving species. Under these conditions, the QD value is reproducible, and it is dependent on the Si|SiO2 interface formed on Si wafers with different orientations. From the analysis of the experimental results with the help of models of the interface, it is shown that the charge QD originates from the dissolution of the suboxides present at the Si|SiO2 interface and from the reconstruction of the surface that appears after the dissolution of the oxide layer. The QD value is affected by the annealing treatment of the sample, suggesting that it can be a good tool for the evaluation of the Si|SiO2 interface structure.