The bonding of Si atoms at the ${\mathrm{SiO}}_2$/Si interface is determined via high-resolution core-level spectroscopy with use of synchrotron radiation. All four oxidation states of Si are resolved, and their distribution is measured for Si(100) and Si(111) substrates. For oxides grown in pure ${\mathrm{O}}_2$, the density of Si atoms in intermediate oxidation states is (1.5±0.5)×${10}^{15}$ ${\mathrm{cm}}^{\mathrm{-}2}$. This value is obtained by measuring the core-level intensity, the escape depth in Si and ${\mathrm{SiO}}_2$, and the relative Si 2p photoionization cross section for different oxidation states. From the density and distribution of intermediate-oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the high density of intermediate-oxidation states (about two monolayers of Si) and by their nonideal distribution. The finite width of the interface is explained by the bond-density mismatch between ${\mathrm{SiO}}_2$ and Si. The electrical properties of the interface (band lineup, Fermi, and vacuum level) are determined. Annealing in ${\mathrm{H}}_2$ is found to influence the electrical parameters by removing the $P_b$ centers that pin the Fermi level. The distribution of oxidation states is not affected.

• Received 7 March 1988

DOI:https://doi.org/10.1103/PhysRevB.38.6084

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Physical Review B 50^th Anniversary Milestones

These Milestone studies represent lasting contributions to physics by way of reporting significant discoveries, initiating new areas of research, or substantially enhancing the conceptual tools for making progress in the burgeoning field of condensed matter physics.