Analysis of gate leakage current in ultra-thin oxide grown by high water vapor pressure thermal oxidation on 4H-SiC

Ultra-thin SiO₂ layers were grown on n-type 4H-SiC by thermal oxidation in high pressure water vapor ambient. The gate leakage current mechanism at low electric fields and different temperatures was studied. The presence of direct tunneling (DT) and Schottky emission (SE) current mechanisms was observed, with DT dominating at low temperature region of up to 393 K and a combination of DT and SE present at higher temperatures of more than 393 K. The effective barrier height between SiC Fermi level and SiO₂ conduction band edge was extracted by fitting the DT model to the experimental gate oxide leakage current density vs. gate oxide electric field curve. It is shown that effective barrier height decreased with increase in temperature and increase in SiC/SiO₂ interface state density (D_it), giving rise to a higher DT current.