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

Abstract

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 GeO[Formula: see text] 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/GeO[Formula: see text]/ZrO[Formula: see text] 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 ZrO[Formula: see text] 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.