Interaction of metal impurities with native oxygen defects in GeO2

Injection of metal atoms from a high-k oxide cap to a passivating GeO2 layer could ultimately affect the quality of Ge-based gate stacks. Here we investigate with first-principles calculations the incorporation of different metal atoms and their effect on the electronic properties of GeO2. We find that tetravalent Hf and Zr substitutional atoms have no beneficial influence on pre-existing defect states in GeO2 whereas trivalent Al species can passivate existing oxygen vacancies. The results are consistent with the improved channel mobility of devices employing Al2O3/GeO2 gate oxides.

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► In the GeO2 interlayer of a Ge/high-k stack, pre-existing oxygen vacancies affect device’s performance.
► Injected metal atoms from the deposited high-k dielectric can substitute Ge atoms and interact with oxygen vacancies.
► The valency of the metal impurity is the key factor for the metal–vacancy interaction.
► Trivalent metal impurities can annihilate oxygen vacancies while tetravalent metals have adverse effects.