Local structure and energy-band alignment of HfO2 and HfO2-La2O3 on strained Si0.65Ge0.35

The local structure, interfacial chemical state and energy-band alignment of plasma-enhanced atomic layer deposited (PEALD) HfO2 and HfO2-La2O3 composite thin films are investigated by synchrotron based extended X-ray absorption fine structure (EXAFS), X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The experimental results show that the valence band offsets (VBOs) of HfO2/SiGe and HfO2-La2O3/SiGe significantly increase after annealing treatment. This can be explained by the proposition that O is transferred from the HfO2 and HfO2-La2O3 layers into the interfacial layer forming positively charged O vacancies and a high internal electronic field built at the interface upon annealing. Moreover, the VBO of HfO2-La2O3/SiGe (3.06 eV) is smaller than that of HfO2/SiGe (3.20 eV), which is mainly due to the enhanced amorphous structure and excellent thermal stability of HfO2-La2O3.