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 O-3 or H2O have been used as oxygen precursors. The valence-band offset (VBO) values, determined by XPS, are 3.0 +/- 0.1 eV and 3.1 +/- 0.1 eV for the samples grown using O-3 and H2O, respectively. A conduction-band offset (CBO) value of 2.0 +/- 0.1 eV has been obtained by IPE for all the samples. Considering a band gap of 5.6 +/- 0.1 eV, 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 O-3 is not affecting the band alignment of the HfO2/Ge heterojunction. (c) 2006 American Institute of Physics.