Probing a nonuniform two-dimensional electron gas with random telegraph signals

Abstract

We observe a sequence of two-level random telegraph signals (RTSs) in the drain/source current of a 1.7 nm gate oxide silicon metal-oxide-semiconductor field-effect transistor. The RTS magnitude is transformed into the apparent Debye length around a negatively charged oxide trap. We achieve excellent reproduction of the Debye data (40 down to 5 nm). This leads to the quantified area spanned by the dominant conductive percolation paths in the underlying two-dimensional electron gas (2DEG). We find that most of the 2DEG in inversion is recovered in a largest threshold voltage sample (similar to 0.35 V), while for the lowest threshold (similar to 0.15 V), a certain conductive filament is likely to occur. The gate direct tunneling current further corroborates the percolation picture. (c) 2008 American Institute of Physics.