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Effects of Interfacial Energetics on the Effective Surface Recombination Velocity of Si/Liquid Contacts

Gstrein, Florian and Michalak, David J. and Royea, William J. and Lewis, Nathan S. (2002) Effects of Interfacial Energetics on the Effective Surface Recombination Velocity of Si/Liquid Contacts. Journal of Physical Chemistry B, 106 (11). pp. 2950-2961. ISSN 1520-6106. doi:10.1021/jp012997d.

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Photoconductivity decay data have been obtained for NH_4F_((aq))-etched Si(111) and for air-oxidized Si(111) surfaces in contact with solutions of methanol, tetrahydrofuran (THF), or acetonitrile containing either ferrocene^(+/0) (Fc^(+/0)), [bis(pentamethylcyclopentadienyl)iron]^(+/0) (Me_(10)Fc^(+/0)), iodine (I_2), or cobaltocene^(+/0) (CoCp_2^(+/0)). Carrier decay measurements were made under both low-level and high-level injection conditions using a contactless rf photoconductivity decay apparatus. When in contact with electrolyte solutions having either very positive (Fc^(+/0), I_2/I^-) or relatively negative (CoCp_2^(+/0)) Nernstian redox potentials with respect to the conduction-band edge of Si, Si surfaces exhibited low effective surface recombination velocities. In contrast, surfaces that were exposed only to N_2(g) ambients or to electrolyte solutions that contained a mild oxidant (such as Me_(10)Fc^(+/0)) showed differing rf photoconductivity decay behavior depending on their different surface chemistry. Specifically, surfaces that possessed Si−OCH_3 bonds, produced by reaction of H-terminated Si with CH_3OH−Fc^(+/0), showed lower surface recombination velocities in contact with N_(2(g)) or in contact with CH_3OH−Me_(10)Fc^(+/0) solutions than did NH_4F_((aq))-etched, air-exposed H-terminated Si(111) surfaces in contact with the same ambients. Furthermore, the CH_3OH−Fc^(+/0)-treated surfaces showed lower surface recombination velocities than surfaces containing Si−I bonds, which were formed by the reaction of H-terminated Si surfaces with CH_3OH−I_2 or THF−I_2 solutions. These results can all be consistently explained through reference to the electrochemistry of Si/liquid contacts. In conjunction with prior measurements of the near-surface channel conductance for p^+−n−p^+ Si structures in contact with CH_3OH−Fc^(+/0) solutions, the data reveal that formation of an inversion layer (i.e., an accumulation of holes at the surface) on n-type Si, and not a reduced density of surface electrical trap sites, is primarily responsible for the long charge carrier lifetimes observed for Si surfaces in contact with CH_3OH or THF electrolytes containing I_2 or Fc^(+/0). Similarly, formation of an accumulation layer (i.e., an accumulation of electrons at the surface) consistently explains the low effective surface recombination velocity observed for the Si/CH_3OH−CoCp_2 and Si/CH_3CN−CoCp_2 contacts. Detailed digital simulations of the photoconductivity decay dynamics for semiconductors that are in conditions of inversion or depletion while in contact with redox-active electrolytes support these conclusions.

Item Type:Article
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URLURL TypeDescription ItemSupporting Information
Michalak, David J.0000-0002-1226-608X
Lewis, Nathan S.0000-0001-5245-0538
Additional Information:© 2002 American Chemical Society. Received 2 August 2001. Published online 22 February 2002. Published in print 1 March 2002. We acknowledge the National Science Foundation, grant CHE-9974562, for support of this research. We also are grateful to Reiner Nürnberg (Weierstrass-Institut, Berlin) and Adrian Lew (Caltech) for helpful discussions relating to the digital simulations.
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Issue or Number:11
Record Number:CaltechAUTHORS:20170519-064910131
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Official Citation:Effects of Interfacial Energetics on the Effective Surface Recombination Velocity of Si/Liquid Contacts Florian Gstrein, David J. Michalak, William J. Royea, and Nathan S. Lewis The Journal of Physical Chemistry B 2002 106 (11), 2950-2961 DOI: 10.1021/jp012997d
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77594
Deposited By: Ruth Sustaita
Deposited On:19 May 2017 15:57
Last Modified:15 Nov 2021 17:32

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