Energy gap and band alignment for (HfO2)x(Al2O3)1−x on (100) Si

High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.