Theoretical investigation of Hf and Zr defects in c-Ge

Abstract

The introduction of high-permittivity gate dielectric materials intocomplementary metal oxide semiconductor technology has reopened the interestin Ge as a channel material mainly due to its high hole mobility. SinceHfO2 and ZrO2 are two of the most promising dielectric candidates, it is important to investigate if Hf andZr may diffuse into the Ge channel. Therefore, using ab initio density functional theorycalculations, we have studied substitutional and interstitial Hf and Zr impurities inc-Ge,looking for neutral defects. We find that (i) substitutional Zr and Hf defects areenergetically more favorable than interstitial defects; (ii) under oxygen-rich conditions,neither Zr nor Hf migration towards the channel is likely to occur; (iii) either under Hf- orZr-rich conditions it is very likely, particularly for Zr, that defects will be incorporated inthe channel.