Full band approach to tunneling in MOS structures

Using atomistic quantum mechanical tight-binding (TB) methods that include the full band structure, we study electron tunneling through three-dimensional models of n⁺-Si/SiO₂/p-Si capacitors with thicknesses between 0.7 and 4.4 nm. We find that the microscopic oxide structure influences transmission coefficients and tunnel currents significantly. The best agreement with experimental current-thickness and current-voltage data is obtained for a model derived from the β-cristobalite polytype of SiO₂ that has a fairly small conduction band mass of 0.34 m₀. Standard approximate effective mass-based methods reproduce the TB results only if an energy and oxide thickness dependence of the mass parameter is introduced.