Fluorination Anodization of n-Type Silicon in the Dark via Schottky-Driven Electron Extraction

Abstract

The band structure of semiconductors governs electron exchange, rendering interfacial electron transfer both controllable and intrinsically time-integrated. Because electron transfer affects the formation and rupture of interatomic bonds, it constitutes the main driving force of chemical and electrochemical reactions. Fluorination anodization of n-type silicon in the dark is traditionally considered impossible because of the scarcity of the required species─holes. Here, we report that sufficiently sustained bias induces fluorination anodization of n-type silicon in complete darkness under standard electrochemical conditions. We attribute this phenomenon to the formation of a Schottky junction at the metal–semiconductor contact. Continuous long-term electron extraction through this interface guides a dynamic charge reconstruction, resulting in hole accumulation and the creation of a provisional inversion layer. Moreover, to validate this Schottky-driven mechanism, we designed a localized laser beam with an irradiation diameter of 1 mm using three distinct wavelengths─corresponding to energies greater than, near, and less than the silicon bandgap─as a probed region during dark electrochemical processing. These experiments reveal that the anodization reaction pathway is controlled by internal carrier redistribution, i.e., self-doped holes. We introduce an “electric-field budget” framework to quantify the cumulative effect of electron transfer and bias duration on electrochemical kinetics. We report that electric-field-induced electron transfer in semiconductors─particularly its time-integrated and cumulative potential dictated by the interfacial energy barrier─enables chemical or electrochemical reactions even without appropriate external excitation.