Energy band alignment of $HfO2$ on Ge

The band alignment of hafnium oxide films grown on Ge (100) by atomic layer deposition has been investigated by x-ray photoelectron spectroscopy (XPS) and internal photoemission (IPE) spectroscopy. $HfO2$ films have been grown using $HfCl4$ as hafnium precursor while $O3$ or $H2O$ have been used as oxygen precursors. The valence-band offset (VBO) values, determined by XPS, are $3.0±0.1eV$ and $3.1±0.1eV$ for the samples grown using $O3$ and $H2O$⁠, respectively. A conduction-band offset (CBO) value of $2.0±0.1eV$ has been obtained by IPE for all the samples. Considering a band gap of $5.6±0.1eV$⁠, as obtained by photoconductivity measurements, XPS and IPE results have been found to be in excellent agreement. The CBO and VBO values are the same in all the samples within the experimental error. The presence of a thick $GeOx$ interfacial layer in the samples grown using $O3$ is not affecting the band alignment of the $HfO2∕Ge$ heterojunction.