Hole injection into silicon dioxide (SiO2) films (8-40 nm thick) is investigated for the first time during substrate electron injection via Fowler-Nordheim (FN) tunneling in n-type 4H-and 6H-SiC (silicon carbide) based metal-oxide-semiconductor (MOS) structures at a wide range of temperatures (T) between 298 and 598 K and oxide electric fields E-ox from 6 to 10 MV/cm. Holes are generated in heavily doped n-type polycrystalline silicon (n(+)-polySi) gate serving as the anode as well as in the bulk silicon dioxide (SiO2) film via hot-electron initiated band-to-band ionization (BTBI). In absence of oxide trapped charges, it is shown that at a given temperature, the hole injection rates from either of the above two mechanisms are higher in n-4H-SiC MOS devices than those in n-6H-SiC MOS structures when compared at a given E-ox and SiO2 thickness (t(ox)). On the other hand, relative to n-4H-SiC devices, n-6H-SiC structures exhibit higher hole injection rates for a given t(ox) during substrate electron injection at a given FN current density j(e, FN) throughout the temperature range studied here. These two observations clearly reveal that the substrate material (n-6H-SiC and n-4H-SiC) dependencies on time-to-breakdown (t(BD)) or injected charge (electron) to breakdown (Q(BD)) of the SiO2 film depend on the mode of FN injections (constant field/voltage and current) from the substrate which is further verified from the rigorous device simulation as well. (C) 2015 Elsevier Ltd. All rights reserved.