Time delay as the origin of oscillations in anodic Si electrodissolution

Silicon is a key semiconductor electrode and is known for exhibiting oscillations during anodic oxidation in fluoride-containing solutions. This article introduces a mathematical model that captures these oscillations. It describes the formation and dissolution of an oxide layer, determining the oxide composition and the electrostatic potential perpendicular to the electrode. Oscillations occur if the following three conditions are met: the etching speed increases with defects in the oxide layer, the defect density decreases with increasing electric field at the Si-oxide interface, and a sufficient time delay exists between production and etching of the oxide. Numerical simulations reproduce experimental results well. Based on these results, we derive a simplified time-delay model. Using linear stability analysis, we confirm the essential role of the time delay for the oscillations. The basic mechanisms are universal and in line with the point defect model for growth and dissolution of passive films on metal electrodes.