The determination of the energy band gaps of thin-gate insulators has been demonstrated from the onsets of the energy-loss spectra of O 1s (or N 1s) photoelectrons. The valence-band lineups of thin high-dielectric-constant (high-k) dielectrics such as Ta2O5, Al2O3, and ZrO2 formed on metals and Si(100) have also been determined by measuring the energy difference between the valence-band density-of-states curves. The energy band diagrams for metal/high-k dielectrics/Si(100) systems have been derived explicitly from considering the measured band gaps, valence-band lineups, electron affinities, and metal work functions in the systems. It is also demonstrated that total photoelectron yield spectroscopy can be used to quantify the energy distributions of both the defect states in high-k gate dielectrics and at the dielectric/Si(100) interfaces over the entire Si band gap without gate formation.
A theoretical model for tunnel leakage current through 1.65–3.90-nm-thick gate oxides in metal-oxide-semiconductor structures has been developed. The electron effective mass in the oxide layer and the Fermi energy in the n+ poly-Si gate are the only two fitting parameters. It is shown that the calculated tunnel current is well fitted to the measured one over the entire oxide thickness range when the nonparabolic E-k dispersion relationship for the oxide band gap is employed. The electron effective mass in the oxide layer tends to increase as the oxide thickness decreases to less than 2.80 nm presumably due to the existence of compressive stress in the oxide layer near the SiO2/Si(100) interface.
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