Conduction mechanisms of oxide leakage current in p-channel 4H-SiC MOSFETs

Electron and hole leakage current conduction mechanisms under a negative gate bias condition in p-channel 4H-SiC MOSFETs were investigated. Electron leakage current from the gate electrode side was dominant when the gate electrode was n(+) poly Si. From the temperature dependence, it was found that the conduction mechanism consists of the Fowler-Nordheim (FN) and the Pool-Frenkel (PF) mechanisms. On the other hand, analysis of hole leakage current was impeded by hot electrons injected from the gate electrode side. To suppress electron injection, Ni was used as a gate electrode. With the Ni-gate MOSFETs, electron injection was suppressed, and it was possible to analyze the hole leakage current mechanism. The analysis revealed that the hole leakage current also consists of both the FN and PF mechanisms. This study reveals that it is important to select an appropriate gate electrode material when applying a high negative gate bias for 4H-SiC MOSFETs.