Band alignment in ultrathin Hf-Al-O/Si interfaces

Band alignment in Hf-Al-O thin films, grown on Si(100) by atomic layer deposition, was determined via x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The changes in conduction band offset, valence band offset, and bandgap were obtained as a function of annealing temperature. The bandgap Eg was found to be 5.7±0.05 eV for as-deposited Hf-Al-O. After annealing at 600 °C, the increase in Eg was 0.2 eV, and then nearly unchanged up to 850 °C. The conduction band offset Δ Ec increased slowly from 0.82±0.05 eV at room temperature to 1.28±0.05 eV at 850 °C. Even though the band profile of Hf-Al-O is still asymmetric with respect to HfO2, it satisfies the minimum requirement for the determination of the carrier barrier height. The band profiles, obtained via reflection electron energy loss spectroscopy, provided us some insight, which is both convenient and at the same time important, into the way to identify high- k dielectric materials, and we also found that the Hf-Al-O is a promising dielectric material for practical applications.