Understanding Correlated Drain and Gate Current Fluctuations

Recently, some experimental groups have observed the occurrence of correlated drain and gate current fluctuations, which indicate that both currents are influenced by the charge state of the same defect. Since the physical reason behind this phenomenon is unclear at the moment, we evaluated two different explanations: The first model assumes that direct tunneling of carriers is affected by the electrostatic field of the charged defect. Interestingly, this model inherently predicts the gate bias and temperature dependences observed in the experiments and is therefore quite promising at a first glance. In the second model, our multi-state defect model is employed to describe trap-assisted tunneling as a combination of two consecutive nonradiative multi-phonon transitions - namely hole capture from the substrate followed by hole emission into the poly-gate. The latter transition is found to be in the weak electron-phonon coupling regime, which requires the consideration of all band states instead of only the band edges. Our investigation shows that the electrostatic model must be discarded since it predicts only small changes in the gate current while the extended variant of the multi-state defect model delivers quite promising results.