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Influence of surface properties on the electrical conductivity of silicon nanomembranes.

Zhao X, Scott SA, Huang M, Peng W, Kiefer AM, Flack FS, Savage DE, Lagally MG - Nanoscale Res Lett (2011)

Bottom Line: Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared.Re-oxidation rates after these treatments also differ.We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
Because of the large surface-to-volume ratio, the conductivity of semiconductor nanostructures is very sensitive to surface chemical and structural conditions. Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared. The sheet resistance of the SiNMs, measured by the van der Pauw method, shows that HF etching produces at least an order of magnitude larger drop in sheet resistance than that caused by VH treatment, relative to the very high sheet resistance of samples terminated with native oxide. Re-oxidation rates after these treatments also differ. X-ray photoelectron spectroscopy measurements are consistent with the electrical-conductivity results. We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

No MeSH data available.


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XPS spectra of 220-nm SiNMs after 30 days exposure to air, compared to oxidized surface. The F peak persists in the HF-treated SiNM. Take-off angle is 45°, pass energy is 89.45 eV.
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Figure 5: XPS spectra of 220-nm SiNMs after 30 days exposure to air, compared to oxidized surface. The F peak persists in the HF-treated SiNM. Take-off angle is 45°, pass energy is 89.45 eV.

Mentions: There is, however, a caution. Low-doped (1015 cm-3) p-type SiNMs with thicknesses of 220 nm or less show inversion of carrier type from p to n, even before any H termination treatments [10]. The conductivity that is measured is due to electrons, even though the material is nominally p-type [1]. This behavior can be due to trapped charges at the interfaces, whose effect becomes noticeable only for thin sheets, where the total number of bulk dopants is low. The sheet resistance returns to the initial (with native oxide) value within 30 days. Figure 5 shows XPS spectra after 30 days exposure to air. The small F 1s core level peak seen in Figure 3 can still be observed after a month of oxidation. The implication is that the trace surface F does not influence the ultimate sheet resistance. It is clear that the surface terminations with HF and vacuum hydrogenation differ and that the passivation induced by HF is much less effective than that induced by clean-H exposure of a vacuum-cleaned surface, but it appears that presence of F does not ultimately play the decisive role in the re-oxidation kinetics.


Influence of surface properties on the electrical conductivity of silicon nanomembranes.

Zhao X, Scott SA, Huang M, Peng W, Kiefer AM, Flack FS, Savage DE, Lagally MG - Nanoscale Res Lett (2011)

XPS spectra of 220-nm SiNMs after 30 days exposure to air, compared to oxidized surface. The F peak persists in the HF-treated SiNM. Take-off angle is 45°, pass energy is 89.45 eV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211497&req=5

Figure 5: XPS spectra of 220-nm SiNMs after 30 days exposure to air, compared to oxidized surface. The F peak persists in the HF-treated SiNM. Take-off angle is 45°, pass energy is 89.45 eV.
Mentions: There is, however, a caution. Low-doped (1015 cm-3) p-type SiNMs with thicknesses of 220 nm or less show inversion of carrier type from p to n, even before any H termination treatments [10]. The conductivity that is measured is due to electrons, even though the material is nominally p-type [1]. This behavior can be due to trapped charges at the interfaces, whose effect becomes noticeable only for thin sheets, where the total number of bulk dopants is low. The sheet resistance returns to the initial (with native oxide) value within 30 days. Figure 5 shows XPS spectra after 30 days exposure to air. The small F 1s core level peak seen in Figure 3 can still be observed after a month of oxidation. The implication is that the trace surface F does not influence the ultimate sheet resistance. It is clear that the surface terminations with HF and vacuum hydrogenation differ and that the passivation induced by HF is much less effective than that induced by clean-H exposure of a vacuum-cleaned surface, but it appears that presence of F does not ultimately play the decisive role in the re-oxidation kinetics.

Bottom Line: Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared.Re-oxidation rates after these treatments also differ.We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
Because of the large surface-to-volume ratio, the conductivity of semiconductor nanostructures is very sensitive to surface chemical and structural conditions. Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared. The sheet resistance of the SiNMs, measured by the van der Pauw method, shows that HF etching produces at least an order of magnitude larger drop in sheet resistance than that caused by VH treatment, relative to the very high sheet resistance of samples terminated with native oxide. Re-oxidation rates after these treatments also differ. X-ray photoelectron spectroscopy measurements are consistent with the electrical-conductivity results. We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

No MeSH data available.


Related in: MedlinePlus