2.7 Possible atomic origin

Ion contamination as an origin of the is excluded by three reasons. First, the capture and emission times are too fast for ion movement. Second, the hysteresis is already observed and nearly unchanged at low temperatures where ion movement is suppressed (e.g. −60 °C). Third, the sign of caused by typical ion contamination such as K⁺ or Na⁺ would be inverted (e.g. a negative for positive bias stress) [118].

Electrically detected magnetic resonance (EDMR) measurements by Gruber et al. in combination with density functional theory (DFT) simulations by Cottom et al. demonstrate that the dominant hyperfine EDMR spectrum at the SiC-SiO₂ interface of Si-face MOSFETs (see. Fig. 2.32) can be understood in terms of carbon dangling bonds (P_bC centers) [5, 119, 120]. The atomic configuration of this defect is shown schematically in Fig. 2.33. Recent work by Gruber shows an increased P_bC signal on a-face devices indicating an increased density of these traps [121]. Due to this, a possible origin of the observed difference in hysteresis could involve the increased carbon density at the surface of the a-face and therefore a higher density of P_bC centers at the SiC-SiO₂ interface. These results fit well to the difference in trap density extracted via the sweep hysteresis and charge pumping measurements. Therefore, P_bC centers are suggested as the most promising defect candidates for the subthreshold hysteresis effect, although this is still based on limited literature and further studies on the electrical responses of carbon dangling bonds are needed.