Ge-related impurities in high-k oxides: Carrier traps and interaction with native defects

Volatilization of a Ge substrate may generate a large number of impurities inside the gate dielectric of a Ge-based device. Here we use density-functional theory calculations to probe the stability of Ge atoms and GeO molecules inside Al2O3 and Y2O3 high-k oxides. We identify the most stable impurity configurations and we show that both types of extrinsic species generate levels inside the energy band gap of the host systems. We also find that Ge and GeO impurities get trapped at O vacancies and replace the vacancy-related carrier traps with different types of levels in the gap. The results identify atomic-scale mechanisms that underlie gate leakage and charge trapping in Ge-based electronic systems.

A GeO impurity is trapped in an oxygen vacancy of a high-k dielectric. The reaction releases energy along with a Ge interstitial atom.Figure optionsDownload as PowerPoint slideHighlights
► Ab initio calculations probe the interactions between Ge-related impurities and high-k dielectrics.
► Ge and GeO impurites are trapped at O vacancy sites.
► Ge-related impurities carrier traps in key high-k dielectrics.
► Hydrogenation is not an effective means of passivation for Ge-related carrier traps.