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.