Impurity bands inn-type Si/SiO2metal-oxide semiconductors

We calculate the density of states (DOS) for ${\mathrm{Na}}^{+}$ impurity bands in n-type Si/${\mathrm{Sio}}_2$ metal-oxide- semiconductor structures with a Hubbard-type model and using as a basis Martin and Wallis single-impurity states. We show that the intrasite correlation energy increases with the applied electric field on the junction. The same occurs with the bandwidth and with the energy corresponding to the maximum in the DOS. This effect is enhanced by an increase in the impurity concentration, ${\mathrm{N}}_{0\mathrm{x}}$. The asymmetry of the DOS explains why the measured binding energy for finite ${\mathrm{N}}_{0\mathrm{x}}$ is smaller than in the single-impurity case.