Electrical characterisation of Si3N4/SiO2 double layers on p-type 6H-SiC
MNOS, MNS and MOS devices have been fabricated on p-type 6H–SiC substrates without epitaxial layers. They have been characterised using high frequency CV, GV, and IV measurements. The high frequency CV characteristics of p-type 6H–SiC MNOS structures indicate a very similar interface quality to p-type 6H–SiC MOS devices. A lower effective fixed insulator charge QI is found in MNOS devices with a higher oxide thickness xox. An xox of 10 nm is effective in avoiding charge instability. The effective fixed insulator charge QI can be modified in the 10 nm oxide SiC MNOS devices by injecting carriers into the nitride. Similar leakage current characteristics compared to p-type 6H–SiC MNS structures have been found for p-type 6H–SiC MNOS devices, but the SiO2/Si3N4 insulator current is lower, particularly for positive electric fields. At the oxide breakdown limit (−10 MV/cm), Poole–Frenkel conduction is observed in the nitride for negative electric fields due to direct tunnelling of holes into the nitride.