Influence of charged impurities on Si inversion-layer electrons

Abstract

A theoretical investigation of various effects of charged impurities in the oxide on electrons in an inversion layer in the Si${\mathrm{O}}_2$-Si(100) metal-oxide-semiconductor structure has been carried out in the quantum limit. For very low electron density we determine ground- and excited-bound-state energies and wave functions exactly and show their dependence on surface field and impurity distance from the interface. In the high-density limit we treat screening and many-body effects by applying the local-density-functional method. The self-consistent potential gives very good agreement with experimentally determined scattering rates and has one fourfold-occupied bound state. The degeneracy of the bound state is not lifted, even if spin- or valley-density-functional methods are applied. For interfaces under stress, where another subband can be occupied, we study the effect of an impurity on the two-component electron gas. While direct comparison with experiments is not possible, the results seem to indicate that in order to understand mobility measurements under stress, scattering mechanisms additional to those present without stress have to be taken into account. The calculations show that there is only a bound state associated with subband 0′ when no states associated with subband 0 are occupied.