Electron tunneling through SiO2/Si structures in scanning tunneling microscopy

We study electron tunneling through SiO2/Si(001) structures in scanning tunneling microscopy (STM), where the oxide thickness ranges from 0.6 to 2.7 nm. Electron tunneling probabilities through the structures are calculated by employing an exactly solvable one-dimensional model. The calculation reproduces the measured I-V characteristics very well. It is shown by experiment and calculation that a region covered by SiO2 is seen as a higher patch than the Si bare surface in a STM topography (constant current mode measurement). The apparent SiO2 thickness in STM topography is comparable to the calculated one for the 0.6 nm SiO2 but appears to be much thinner than the calculated one for the 2.7 nm SiO2. Origin of the discrepancy is discussed in terms of the electron scattering at the interfaces and in the bulk of SiO2 films.