Interface characterization of high-k dielectrics on Ge substrates

High-k films are currently deposited on Ge substrate to compensate the mobility loss as Ge offers higher mobility compared to that of silicon. This work deals with the electrical characterization of high-k/Ge interface with Hf-based dielectrics on germanium substrate. Characteristics such as hysteresis, leakage current density, interface state density and flatband voltage shift using I–V, C–V and conductance measurements were performed on Ge/HfO2 MOS capacitors. The results suggest that for thermally evaporated HfO2, the interface trap density at HfO2/Ge interface was found to be in the range of 1012–1013 cm−2 eV−1 after 550 °C annealing in N2 ambient even though significant improvements in hysteresis and leakage current were observed. Higher interface state density is attributed to the growth of interfacial layer. XPS analysis confirmed that after annealing, the gate dielectric was composed of both HfO2 and GeO2. Furthermore, various interface treatments such as surface nitridation of Ge performed prior to HfO2 deposition with an exposure to an atomic N beam from a remote RF source or introduction of SiO2 by oxidizing a few monolayers of silicon deposited on Ge substrates, were considered. Even though improvements were observed, the surface nitrided devices demonstrated major dispersion in inversion region as a function of measured frequency as compared to non-nitrided devices. Introduction of SiO2 seems to improve the interface quality marginally.