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Interfacial Energetics of Silicon in Contact with 11 M NH_4F(aq), Buffered HF(aq), 27 M HF(aq), and 18 M H_2SO_4

Michalak, David J. and Gstrein, Florian and Lewis, Nathan S. (2007) Interfacial Energetics of Silicon in Contact with 11 M NH_4F(aq), Buffered HF(aq), 27 M HF(aq), and 18 M H_2SO_4. Journal of Physical Chemistry C, 111 (44). pp. 16516-16532. ISSN 1932-7447. doi:10.1021/jp074971d.

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Open-circuit impedance spectra, channel impedance spectroscopy on solution-gated field-effect devices, and differential capacitance vs potential (Mott−Schottky) measurements were used to determine the energetics of n-Si(111), n-Si(100), and p-Si(111) electrodes in contact with aqueous 11 M (40% by weight) NH_4F, buffered HF (BHF), 27 M (48%) HF(aq), and concentrated (18 M) H_2SO_4. A Mott−Schottky analysis of A_s^2C_(sc)^(-2)-vs-E (where As is the interfacial area, and C_(sc) is the differential capacitance as a function of the electrode potential, E) data yielded reliable barrier heights for some silicon/liquid contacts in this work. Performing a Mott−Schottky analysis, however, requires measurement of the differential capacitance under reverse bias, where oxidation or etching can occur for n-Si and where electroplating of metal contaminants can occur for p-Si. Hence, open-circuit methods would offer desirable, complementary approaches to probing the energetics of such contacts. Accordingly, open-circuit, near-surface channel conductance measurements have been performed using solution-gated n^+-p-Si(111)-n^+ and p^+-n-Si(100)-p^+ devices. Additionally, open-circuit impedance spectra were obtained for silicon electrodes in contact with these solutions. The combination of the three techniques indicated that the surfaces of n-Si(111) and n-Si(100) were under accumulation when in contact with either 11 M NH_4F(aq) or BHF(aq). The barrier heights for n-Si(111) and n-Si(100) in 11 M NH_4F(aq) were −0.065 ± 0.084 V and −0.20 ± 0.21 V, respectively, and were −0.03 ± 0.19 V and −0.07 ± 0.24 V, respectively, for these surfaces in contact with buffered HF(aq). Consistently, p-Si(111) surfaces were determined to be in inversion in contact with these electrolytes, exhibiting barrier heights of 0.984 ± 0.078 V in contact with 11 M NH_4F(aq) and 0.97 ± 0.22 V in contact with buffered HF(aq). In contact with 27 M HF(aq), n-Si(111) and n-Si(100) were in depletion, with barrier heights of 0.577 ± 0.038 V and 0.400 ± 0.057 V, respectively, and p-Si(111) was under inversion with a barrier height of 0.856 ± 0.076 V. Measurements performed in 18 M H_2SO_4 revealed barrier heights of 0.75 ± 0.11 V, 0.696 ± 0.043 V, and 0.889 ± 0.018 V for n-Si(111), n-Si(100), and p-Si(111), respectively, demonstrating that in 18 M H_2SO_4, the band edge positions of Si were different for different doping types. The barrier height data demonstrate that the observed low recombination rates of silicon in contact with 11 M NH_4F, BHF, or 18 M H_2SO_4 cannot necessarily be attributed to a reduction in the number of surface trap states. In part, low surface recombination rates are expected for such systems because the very large or very small barrier height for silicon in contact with these liquids provides a potential barrier that prevents one type of photogenerated carrier (either electrons or holes) from reaching the surface, thereby producing a low steady-state surface recombination rate.

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Michalak, David J.0000-0002-1226-608X
Lewis, Nathan S.0000-0001-5245-0538
Additional Information:© 2007 American Chemical Society. Received 26 June 2007. Published online 12 October 2007. Published in print 1 November 2007. We acknowledge the NSF, Grant CHE-0604894, for support of this work. DJM also acknowledges the generous support of a Link Foundation Energy Fellowship.
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Link FoundationUNSPECIFIED
Issue or Number:44
Record Number:CaltechAUTHORS:20170616-143033829
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Official Citation:Interfacial Energetics of Silicon in Contact with 11 M NH4F(aq), Buffered HF(aq), 27 M HF(aq), and 18 M H2SO4 David J. Michalak, Florian Gstrein, and Nathan S. Lewis The Journal of Physical Chemistry C 2007 111 (44), 16516-16532 DOI: 10.1021/jp074971d
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78297
Deposited By: Ruth Sustaita
Deposited On:16 Jun 2017 22:04
Last Modified:15 Nov 2021 17:38

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