Direct and trap-assisted elastic tunneling through ultrathin gate oxides

The direct and assisted-by-trap elastic tunnel current in metal-oxide-semiconductor capacitors with ultrathin gate oxide (1.5-3.6 nm) has been studied. Bardeen's method has been adapted to obtain the assisted tunnel current, in addition to the direct tunnel current. The dependence of the assisted current on the trap distribution in energy has also been analyzed. This allows us to obtain the trap distribution in energy from experimental current curves. Finally, we have analyzed the role of the image force, the inclusion of which can avoid a barrier height dependence on the oxide thickness.