Evidence of hole direct tunneling through ultrathin gate oxide using P/sup +/ poly-SiGe gate

P/sup +/ poly-Si and poly-Si/sub 0.75/Ge/sub 0.25/-gated PMOS transistors with ultrathin gate oxides of 25 and 29 /spl Aring/ were used for this study. The difference in the gate work function was used to determine the mechanisms of gate tunneling current in such thin gate oxides, Under negative gate bias (inversion bias), it was found that the source/drain terminal serves as a source of holes for small V/sub g/ value, and as gate bias increases (more negative), it becomes a hole sink. These observations can be interpreted in terms of two competing mechanisms. For the first time, hole direct tunneling is reported, Hole direct tunneling is the dominant mechanism for -2 V