XPS and IPE analysis of HfO2 band alignment with high-mobility semiconductors

A detailed analysis of the band alignment between atomic-layer deposition (ALD)-grown HfO2 thin films and n-type Ge(1 0 0) substrate is presented. The valence band offset (VBO) is determined by X-ray photoelectron spectroscopy (XPS) after careful evaluation of the experimental data and accurate removal of the artefacts induced by differential charging phenomena occurring during XPS measurement. VBO values are 2.7±0.1 eV for all samples independent of the different growth conditions. A conduction band offset (CBO) of 2.0±0.1 eV and a band gap of 5.6±0.1 eV have been obtained by internal photoemission (IPE) and photoconductivity measurements, respectively. VBO and CBO values obtained by the different techniques are in excellent agreement within the experimental error.