Electrical characteristics of Ge/GeOx(N)/HfO2 gate stacks

The electrical properties of Ge-based metal–oxide–semiconductor devices with GeOx(N)/HfO2 gate stacks are investigated. The current–voltage characteristics of the structures are consistent with the tunneling effect, with a transition from Fowler–Nordheim tunneling to direct tunneling as the HfO2 layer thickness is decreased. The capacitance–voltage characteristics of the MOS structures with HF-last Ge surfaces show large frequency-dispersions, indicative of a high density (∼1013 cm−2) of interface states. Much reduced frequency dispersion in the capacitance–voltage characteristics is observed on capacitors with NH3 annealed surfaces. In this case, however, a bump appears near the flat-band voltage of the devices, which we attribute to interface defects and/or border traps related to nitrogen.