The mechanism of improving germanium metal–oxide–semiconductor field-effect transistors’ reliability by high-k dielectric and yttrium-doping: From the view of charge trapping

The application of germanium (Ge)-based transistors has long been restricted by the poor reliability of the gate dielectrics. One solution proposed in the experiment is capping the GeO2 layer with high-k dielectrics and further doping the dielectric with yttrium (Y) atoms. However, the strategy only works at a very small doping concentration window, and the underlying mechanism remains unclear. Here, we carry out first-principles calculations on a concrete Ge/GeO2/ZrO2 stack to study the structural and electronic properties of various defects before and after Y-doping and further calculate their exact charge-trapping rates by the Marcus charge transfer theory. We show that the Y atoms can effectively weaken the charge-trapping capability of vacancy defects in the ZrO2 layer, but on the other hand, they can induce some new types of active defects if the density is high. In addition, it is found that the Y atoms can have a very different effect even when doped to the same material. These results indicate that a precise control of the doping position and doping concentration is necessary to promote the reliability of Ge transistors.