## On the Validity of the Harmonic Potential Energy Surface Approximation for Nonradiative Multiphonon Charge Transitions in Oxide Defects

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IWCE Presentation. Hole trapping in oxide defects in the gate insulator of MOSFET transistors has been linked to a wide range of phenomena like random telegraph noise, 1/f noise, bias temperature instability (BTI), stress-induced leakage current and hot carrier degradation [1–5]. Charge capture (τc ) and emission (τe ) times of a defect are theoretically described by nonradiative-multiphonon (NMP)-theory, where the potential energy surface (PES) along the reaction coordinate is usually approximated by a parabola [2, 6, 7]. In the classical high-temperature limit, transitions between the different charge states occur at the intersection of those parabolas, which also defines the classical reaction barrier. This harmonic approximation has been in use ever since the introduction of NMP-theory [8–10]. However,the quality of this approximation is rarely investigated [7]. In this work, we compare different approximations of the PES in order to calculate τc and τe and compare them to the results obtained by Density Functional Theory (DFT) calculations. For this we use the DFT-PES as well as two approximations of the PES of several defects to calculate τc and τe in a pMOS device. Our study covers different possible defect candidates, which have been previously identified as sources of degradation in silicon dioxide [11–13]: The oxygen vacancy (OV, see Fig. 1b) in α-quartz, the hydrogen bridge (HB, see Fig. 1c) in both α-quartz and in amorphous silicon dioxide (a-SiO2) and the hydroxyl E’ center (H-E’, see Fig. 1d) in a-SiO2. Since the amorphous structures differ from each other, also the PES varies. Therefore we have investigated 11 HB defects and 12 H-E’ defects from [14] to provide statistical data. We show that the parabolic fit to the PES underestimates τc and τe by several orders of magnitude. Therefore we propose a different approximation that yields to more accurate τc and τe and captures several desired features, also in cases where the parabolic approximation fails.

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In collaboration with A.-M. El-Sayed, T. Grasser, Vienna University of Technology,and A.L. Shluger, University College London.

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North Ballroom, PMU, Purdue University, West Lafayette, IN