Modeling of Defect Related Reliability Phenomena
in SiC Power-MOSFETs
As only briefly outlined in this chapter, the variety of defect candidates that potentially form in SiC/SiO2 structures is much larger compared to Si/SiO2. Their calculated thermodynamic trap levels are distributed over the whole oxide band gap. Moreover, as the active energy regions for negative and positive transistor operation show, almost the entire SiO2 band gap can be scanned by deliberately altering the gate bias, suggesting that thermodynamic charge transitions are possible with almost any candidate proposed. The introduction of another atomic species in the substrate compared to pure Si, namely carbon, gives rise to the formation of additional carbon-dangling bonds at the interface to its native oxide with defect levels in the upper half of the SiC band-gap. Those are likely passivated to a large fraction by N, which when incorporated is also suspected to form traps with defect levels suitable for positive charge accumulation and also form acceptor like states close to the SiC conduction band edge. In Chapter 5, the parameters, i.e. thermodynamic trap level, relaxation energies and defect densities, obtained from ab-initio calculations of most likely defect candidates to explain charge transfer reactions causing BTI and TAT in SiC/SiO2 structures are compared with those used for defects in the presented device simulations.