An investigation by AFM and TEM of the mechanism of anodic formation of nanoporosity in n-InP in KOH

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O'Dwyer, Colm
Buckley, D. Noel
Sutton, David
Serantoni, M.
Newcomb, Simon B.
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The early stages of nanoporous layer formation, under anodic conditions in the absence of light, were investigated for n-type InP with a carrier concentration of ∼3× 1018 cm-3 in 5 mol dm-3 KOH and a mechanism for the process is proposed. At potentials less than ∼0.35 V, spectroscopic ellipsometry and transmission electron microscopy (TEM) showed a thin oxide film on the surface. Atomic force microscopy (AFM) of electrode surfaces showed no pitting below ∼0.35 V but clearly showed etch pit formation in the range 0.4-0.53 V. The density of surface pits increased with time in both linear potential sweep and constant potential reaching a constant value at a time corresponding approximately to the current peak in linear sweep voltammograms and current-time curves at constant potential. TEM clearly showed individual nanoporous domains separated from the surface by a dense ∼40 nm InP layer. It is concluded that each domain develops as a result of directionally preferential pore propagation from an individual surface pit which forms a channel through this near-surface layer. As they grow larger, domains meet, and the merging of multiple domains eventually leads to a continuous nanoporous sub-surface region.
Indium compounds , III-V semiconductors , Porous semiconductors , Nanoporous materials , Porosity , Electrochemical electrodes , Anodes , Atomic force microscopy , Transmission electron microscopy , Ellipsometry , Voltammetry (chemical analysis) , Carrier density , Etching , Surface structure
O'Dwyer, C., Buckley, D. N., Sutton, D., Serantoni, M. and Newcomb, S. B. (2007) 'An investigation by AFM and TEM of the mechanism of anodic formation of nanoporosity in n-InP in KOH', Journal of the Electrochemical Society, 154(2), pp. H78-H85.
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