A semi-empirical model for the tunnel current-voltage characteristics in Al-SiO2-Si(p) structures

The current-voltage characteristics of forward biased Al-SiO2-Si(p) tunnel diodes having insulator thicknesses in the 20-70 Angstrom range are investigated in this work. A simple model based on the WKB approximation is presented for the direct tunnel process, which fits the experimental curves and their derivatives. The resulting expression corresponds in a natural way to common expressions for Fowler-Nordheim tunneling, extending its validity to thick oxides. The salient features of the model are a constant value for the wave vector in the calculation of the tunneling probability (k(o) = 0.376 Angstrom(-1)) and an attenuation factor in the current integral, which expresses the current contribution of electrons tunneling directly into the silicon to decrease exponentially with the energy distance to the top of the barrier at the SiO2-Si interface. In addition, the dependence of the logarithmic derivative of the current on the applied voltage has been investigated and used to discriminate between different models.