Effects of thermal annealing on the band alignment of lanthanum aluminate on silicon investigated by x-ray photoelectron spectroscopy

Abstract

In this work, we investigate the changes in the band offsets of lanthanum aluminate on silicon after postdeposition annealing at 600 and 800 °C by x-ray photoelectron spectroscopy (XPS). It is found that annealing at 800 °C reduces the conduction band offset from 2.31 to 1.39±0.2 eV. A detailed analysis is performed to ascertain the origin of the changes. We will show that the observed band offset changes are not a consequence of alterations in the bulk properties of the oxide film, but rather a true band alignment change between the two materials. After systematically considering “artefacts” of XPS measurements, including extra-atomic relaxation and differential charging, we conclude that the band offset changes originate mainly from an interfacial effect. While intrinsic gap states dipoles are not sufficient to account for the large band offset shifts, we turned our attention to examine the interface of the gate oxide stack. We show the existence of at least two types of dipoles. One of the dipoles exists at the silicon-silicon oxide interface, while the strength of the other dipole can be correlated with the thickness and the chemical stoichiometry of the interfacial silicate.