Kaviani, M; Afanas'ev, VV; Shluger, AL; (2017) Interactions of hydrogen with amorphous hafnium oxide. Physical Review B , 95 (7) , Article 075117. 10.1103/PhysRevB.95.075117.

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Abstract

We used density functional theory (DFT) calculations to study the interaction of hydrogen with amorphous hafnia ( a − HfO 2 ) using a hybrid exchange-correlation functional. Injection of atomic hydrogen, its diffusion towards electrodes, and ionization can be seen as key processes underlying charge instability of high-permittivity amorphous hafnia layers in many applications. Hydrogen in many wide band gap crystalline oxides exhibits negative-U behavior (+1 and − 1 charged states are thermodynamically more stable than the neutral state) . Our results show that in a − HfO 2 hydrogen is also negative-U, with charged states being the most thermodynamically stable at all Fermi level positions. However, metastable atomic hydrogen can share an electron with intrinsic electron trapping precursor sites [Phys. Rev. B 94, 020103 (2016).] forming a [ e − t r + O – H ] center, which is lower in energy on average by about 0.2 eV. These electron trapping sites can affect both the dynamics and thermodynamics of the interaction of hydrogen with a − HfO 2 and the electrical behavior of amorphous hafnia films in CMOS devices.

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