Modulation of the charge of a single-electron transistor by distant defects

We have systematically measured two-level fluctuator (TLF) noise in a single-electron tunneling transistor. From the amplitude, duty cycle, and presence of intermediate states, we conclude that there is a cluster of triggered TLF's in this case. The systematic dependence of switching rate on gate voltage, and the lack of rate dependence on a finer scale or on source-drain voltage, tell us unambiguously that the TLF's are not located in the tunnel barriers. We thus conclude, as has been previously inferred, that noisy defects outside the barrier can lead to significant modulation of the transistor island charge (up to about 0.2 e).