Suppression of ambipolar behavior in metallic source/drain metal-oxide-semiconductor field-effect transistors

We present a study on suppressing the ambipolar behavior of Schottky barrier metal-oxide-semiconductor field-effect transistors (MOSFET). Inserting a silicon nitride layer of appropriate thickness between the metallic source/drain electrodes and the silicon yields a low Schottky-barrier and simultaneously tunes the properties of the contact from metal-semiconductor-like to the behavior of a doped contact. Moreover, device characteristics of pseudo-MOSFETs reveal an efficient suppression of ambipolar behavior. Comparison with an alternative way of achieving low Schottky-barrier contacts, i.e., by inserting a strong dipole layer such as LiF between the metal and the silicon, reveals that the suppression is not a result of shifting the Fermi level closer to the conduction band but is caused by a reduction of metal-induced gap states. The trade-off between suppression of the ambipolar behavior, contact length and on-state current is investigated with simulations. © 2009 American Institute of Physics.