Effect of Electrolyte Concentration on Anodic Nanoporous Layer Growth for n-InP in Aqueous KOH

摘要

The surface morphology and sub-surface porous structure of (100) n-InP following anodization in 1-10 mol dm{sup}(-3) aqueous KOH were studied using linear sweep voltammetry (LSV) in combination with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). LSV of n-InP in 10 mol dm{sup}(-3) KOH showed a single anodic current peak at 0.41V. As the concentration of electrolyte was decreased, the peak increased in current density and charge and shifted to more positive potentials; eventually individual peaks were no longer discernable. Porous layers were observed in SEM cross-sections following linear potential sweeps and the porous layer thickness increased significantly with decreasing KOH concentration, reaching a maximum value at ～2.2 mol dm{sup}(-3). At concentrations less than 1.8 mol dm"3 the layer thickness decreased sharply, pore diameters became wider and pore walls became narrower until eventually, at 1.1 mol dm{sup}(-2) or lower, no porous layers were observed. It was also observed that the pore width increased and the inter-pore spacing decreased with decreasing concentration. It is proposed that preferential pore propagation occurs along <111> directions, contrary to previous suggestions, and that the resulting nanoporous domains, initially formed, have triangular cross-sections when viewed in one of the {110} cleavage planes, 'dove-tail' cross-sections viewed in the orthogonal {110} cleavage plane and square profiles when viewed in the (100) plane of the electrode surface.