The band gap and band offset in ultrathin oxide-semiconductor heterostructures

In ultrathin high-k oxide layers knowledge of the band line up and band gap is essential for modeling the transport properties and to learn about a device's long term stability and reliability. However, such data are hard to determine in such ultrathin layers and usually are extrapolated from values for bulk samples or are taken from the literature. In our in situ approach we use electron energy loss spectroscopy, valence band photoelectron spectroscopy, X-ray absorption spectroscopy, and resonant inelastic X-ray scattering to obtain the loss function and the valence and conduction band densities of states. From such data we derive the values of the band offsets and of the band gap. We discuss the ability of this combination of different techniques for the analysis of such complex ultrathin dielectric systems and discuss in detail the properties of the native oxide in SiO2/Si(001) and SiO2/3C−SiC(001).