Band gap and band offsets for ultrathin (HfO2)x(SiO2)1−x dielectric films on Si (100)

Energy band profile of ultrathin Hf silicate dielectrics, grown by atomic layer deposition, was studied by using x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap energy only slightly increases from $5.52\mathrm{eV}$ for ${\left(\mathrm{Hf}{\mathrm{O}}_2\right)}_{0.75}{\left(\mathrm{Si}{\mathrm{O}}_2\right)}_{0.25}$ to $6.10\mathrm{eV}$ for ${\left(\mathrm{Hf}{\mathrm{O}}_2\right)}_{0.25}{\left(\mathrm{Si}{\mathrm{O}}_2\right)}_{0.75}$ , which is much smaller than $8.90\mathrm{eV}$ for $\mathrm{Si}{\mathrm{O}}_2$ . For ultrathin Hf silicate dielectrics, the band gap is mainly determined by the Hf $5d$ conduction band state and the O $2p$ valence band state. The corresponding conduction band offsets are in the vicinity of $1\mathrm{eV}$ , which satisfies the minimum requirement for the carrier barrier heights.