Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 36: Postersitzung (Elektronische Struktur, Grenzfl
äche fest-flüssig, Halbleiteroberfl
ächen und -grenzfl
ächen, Nanostrukturen, Oberfl
ächenreaktionen, Teilchen und Cluster, Struktur und Dynamik reiner Oberfl
ächen)
O 36.1: Poster
Montag, 7. März 2005, 15:00–18:00, Poster TU F
A Four Point Probe Investigation of the Surface Conductivity of Si(111)-7x7 — •J. Wells1, T.M. Hansen2, and Ph. Hofmann1 — 1iNano Center, Aarhus University, Aarhus, Denmark — 2National Institute for Materials Science (NIMS), Nanomaterials Laboratory (NML), Tsukuba, Japan
An in-vacuum 4 point probe has recently been developed which allows more direct measurements of conductivity to be made than is possible with non-contact methods. As a demonstration of the technique, Si(111)-7x7 has been measured under UHV conditions between 70 K and 300 K. Although this surface has already been studied with many techniques, the nature of the surface conductivity still remains unclear and published estimates vary between 10−9 Ω −1 and 10−4 Ω −1.
The silicon surface has been modeled as an infinite sheet separated from a semi-infinite bulk by a charge depletion layer. When the probe spacing is sufficiently small, and at low temperatures, the 4 point probe conductivity is saturated by the surface component whereas at higher temperatures (or larger probe spacings), the bulk component dominates the measurement. Between these two extremes, the measurement is limited by the conduction across the charge depletion layer, and this is temperature dependent.
Our measurements show that the temperature dependence of the conductivity is accurately described by this model. Both the high and low temperature saturations are observable, and from this, this surface conductivity is estimated as 6 x 10−9 Ω −1, consistent with a semiconducting surface state.