Single- Versus Multi-Step Trap Assisted Tunneling Currents—Part II: The Role of Polarons

Abstract

Using the framework developed in the first part of this work, we demonstrate the capabilities of the extended two-state nonradiative multi-phonon (NMP) model by reproducing leakage current characteristics of two selected technologies. First, we identify the temperature-activated leakage mechanism in SiC / SiO₂ stacks using a tens of nanometer thick thermally grown oxide as trap-assisted tunneling (TAT) through defects. Interestingly, this effect can be reproduced with the same parameters in a SiC / SiO₂ stack with deposited oxide. Our simulations demonstrate that these charge transition centers are distributed within only a few nanometers from the SiC / SiO₂ interface. The low thermal activation of the leakage current is linked to the low relaxation energies of the involved traps compared with those typically involved in bias temperature instability (BTI) and Random Telegraph Noise (RTN). Second, a similar mechanism can explain TAT characteristics and transient charge trapping currents in Metal-Insulator-Metal (MIM) capacitors with a ZrO₂ insulating layer. By comparison of our model parameters to theoretical density functional theory (DFT) calculations, we identify self-trapped electrons (polarons) as a likely cause for these effects, as they have the required low relaxation energies.