Image Force Effects and the Dielectric Response of SiO2 in Electron Transport across MOS Structures

Copyright © (1997) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics

        Hot electrons of variable energy were injected from a scanning tunneling microscope (STM) tip into a Pd/SiO2/Si(100) MOS structure. An analysis of the emerging collector current in the Si substrate, a technique known as Ballistic Electron Emission Microscopy (BEEM), revealed a monotonic barrier height lowering with increasing positive oxide bias, in excellent agreement with a scaled classical image force theory. Calculations using the WKB approximation suggest a negligible contribution to the observed shifts from electrons tunneling through the barrier. From an extrapolation to zero oxide field the Pd-SiO2 barrier height of 4.08plusmin0.02 eV was deduced. An image-force-dielectric constant of 2.74 in-between the so-called optical (2.15) and static (3.9) dielectric constant was determined. In order to understand this intermediate value, a theoretical calculation of a retarded image force on the moving electron is carried out for the first time. The calculations yield an image-force-dielectric constant of 2.69, that is consistent with the experimentally determined value. This intermediate dielectric constant is evidence for electron-phonon intercation and corresponds to an average dielectric response integrated over the time of progression of the electron in SiO2.

By: H. J. Wen, R. Ludeke, D. M. Newns and S. H. Lo

Published in: Journal of Vacuum Science and Technology A, volume 15, (no 3), pages 784-9 in 1997

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