Electrochemical formation of nanoporosity in n-InP anodes in KOH

Abstract

We review our recent work on anodic formation of nanoporosity in n-InP in aqueous KOH. Typically, a nanoporous sub-surface region is formed beneath a thin, dense near-surface layer. Atomic force microscopy (AFM) shows pit formation on the surface in the earlier stages of etching, and transmission electron microscopy (TEM) shows individual nanoporous domains separated from the surface by a thin InP layer. Each domain develops from a surface pit. We developed a model based on propagation of pores along the <111>A directions. The model predicts porous domains with a truncated tetrahedral shape and this was confirmed by scanning electron microscopy (SEM) and TEM. Pores are cylindrical and have well-developed facets only near their tips. No porous layers are observed at a KOH concentration of 1.1 mol dm -2 or lower. Linear sweep voltammograms (LSVs) show a pronounced anodic peak corresponding to the formation of the porous region. We describe a technique to deconvolute the effects of potential and time in LSVs and explain their shape and their relationship to porous layer formation.