Enhanced tunnel current through thin oxide due to single-defect scattering

We have studied the conduction current from an n-silicon substrate to n(+)- polycrystalline-silicon gate through an ultrathin oxide layer. Carrier tran smission through the thin oxide layer is enhanced by the presence of an ion ized impurity in the oxide layer. In addition to the normal direct tunnel c urrent, the Coulomb potential of the ionized impurity provides extra conduc tion channels for carriers in the n-silicon substrate to transmit to the po lycrystalline-silicon gate. It has been found that the ratio between the co nduction current through the extra conduction channels and the direct tunne l current can be as large as 1.9. The exact value of the ratio depends on t he location of the charge in the oxide layer. (C) 2001 American Institute o f Physics.