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 $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}$ grown on (100) Si substrate with different ${\mathrm{HfO}}_2$ mole fraction x. Al $\text{2p,}$ Hf $\text{4f,}$ O $\text{1s}$ core levels spectra, valence band spectra, and O $\text{1s}$ energy loss all show continuous changes with x in $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}.$ These data are used to estimate the energy gap ${\mathrm{(E}}_g)$ for $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}},$ the valence band offset ${\mathrm{(\Delta E}}_{\nu })$ and the conduction band offset ${\mathrm{(\Delta E}}_c)$ between $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}$ and the (100) Si substrate. Our XPS results demonstrate that the values of $E_g,$ ${\mathrm{\Delta E}}_{\nu },$ and ${\mathrm{\Delta E}}_c$ for $({\mathrm{HfO}}_2{)}_x({\mathrm{Al}}_2{\mathrm{O}}_3{)}_{\text{1−x}}$ change linearly with x.