Influence of Solvents in HF Solutions on Anodic Formation of Mesoporous Silicon, Revealed by the Characterization of Mesoporous Silicon Rugate Filters

Abstract

Formation mechanism of mesoporous silicon by electrochemical dissolution is studied. HF solutions containing a high amount of alcohol were often used for the preparation of mesoporous silicon. The present study focuses the role of alcohol in the HF electrolyte solutions during the anodic formation of mesoporous silicon. To obtain the dynamic information of mesoporous silicon formation, mesoporous silicon rugate filters that is formed by applying a sinusoidal current density is studied in detail. By analyzing the thickness of multilayers as well as the optical spectra of mesoporous silicon rugate filters, gradual change of the local dissolution condition in the vicinity of pore tips is investigated. Deviation of microscopic thickness of rugate filters is prominent when tert-butanol is used as solvent for HF solution. The deviation becomes less remarkable using methanol or ethanol as solvent. However, a nearly ideal porous silicon rugate filters are obtained in an aqueous HF solution containing a surfactant. This study shows that roles of alcohols are not limited to the reduction of surface tension. Their conductivities also have an impact on the dissolution kinetics.