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Hydrogen bubbles and formation of nanoporous silicon during electrochemical etching
Author(s) -
Saraf Laxmikant,
Baer Donald R.,
Wang Zheming,
Young James,
Engelhard Mark H.,
Thevuthasan S.
Publication year - 2005
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.2048
Subject(s) - nanoporous , nanopore , etching (microfabrication) , silicon , materials science , x ray photoelectron spectroscopy , oxide , hydrogen , chemical engineering , nanotechnology , electrochemistry , chemical physics , analytical chemistry (journal) , chemistry , layer (electronics) , electrode , optoelectronics , metallurgy , organic chemistry , engineering
Many nanoporous Si structures, including those formed by common electrochemical etching procedures, produce a uniformly etched nanoporous surface. If the electrochemical etch rate is slowed down, details of the etch process can be explored and process parameters may be varied to test hypotheses and obtain controlled nanoporous and defect structures. For example, after electrochemical etching of heavily n‐doped ( R = 0.05–0.5 Ω·cm) silicon 〈100〉 single crystals at a current density of 10 mA cm −2 in buffer oxide etch (BOE) electrolyte solution, defect craters containing textured nanopores were observed to occur in ring‐shaped patterns. The defect craters apparently originate at the hydrogen/BOE bubble interface, which forms during hydrogen evolution in the reaction. The slower hydrogen evolution due to low current density and high BOE viscosity allows sufficient bubble residence time so that a high defect density appears at the bubble edges where local reaction rates are highest. Current‐carrying SiOH species are most likely responsible for the widening of the craters. Reducing the defect/doping density in silicon lowers the defect concentration and thereby the density of nanopores. Measurements of photoluminescence lifetime and intensity show a distinct feature when the few nanopores formed at the ring edges are isolated from each other. Overall features observed in the photoluminescence intensity by XPS strongly emphasize the role of surface oxide that influences these properties. Copyright © 2005 John Wiley & Sons, Ltd.