Hydrogen bubbles and formation of nanoporous silicon during electrochemical etching
Article first published online: 7 APR 2005
Copyright © 2005 John Wiley & Sons, Ltd.
Surface and Interface Analysis
Volume 37, Issue 6, pages 555–561, June 2005
How to Cite
Saraf, L., Baer, D. R., Wang, Z., Young, J., Engelhard, M. H. and Thevuthasan, S. (2005), Hydrogen bubbles and formation of nanoporous silicon during electrochemical etching. Surf. Interface Anal., 37: 555–561. doi: 10.1002/sia.2048
- Issue published online: 23 MAY 2005
- Article first published online: 7 APR 2005
- Manuscript Revised: 11 FEB 2005
- Manuscript Accepted: 11 FEB 2005
- Manuscript Received: 9 SEP 2004
- Pacific Northwest National Laboratory.
- nanoporous Si;
- hydrogen bubbles;
- H2/BOE/Si triple interface
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.