Interactions of hydrogen with amorphous hafnium oxide

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 − tr + 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.

Ligand-Dependent Energetics for Dehydrogenation: Implications in Li-Ion Battery Electrolyte Stability and Selective Oxidation Catalysis of Hydrogen-Containing Molecules

“…In all other cases, hydrogen adsorbs as H + on the anionic ligand and an electron into the conduction band or at localized states close to the conduction band. This general trend can be complicated by the presence of defects, which can introduce additional trapping levels in the band gap, 105,106 disorder, as reported for the hydrogen defect on amorphous silica, 107,108 or coadsorbed species which allows for Lewis acid/base pair adsorption. 109 Secondly, the descriptors that we have identified for the hydrogen adsorption energy, which rely on the position of the ligand states, the band gap and the metal-ligand bond length, can serve to identify and predict materials with adsorption properties suitable for a given applications.…”

The origin of negative charging in amorphous Al2O3 films: the role of native defects

“…To achieve that, we calculate the defect properties in ten statistically independent cells obtained using the method described above and in refs. 49,50 . This allows a variety of local defect geometries to be sampled, which have different bond lengths and local coordination numbers, whilst also allowing for variation in bulk properties that can affect the stability of certain defect configurations and charge states.…”

The role of the disordered HfO2 network in the high-κ n-MOSFET shallow electron trapping

“…The amorphous HfO 2 features various Hf-O-Hf atomic networks that can be found in the supercell, and as revealed in the early studies, disorders of the atomic network typically induces electron traps, which is also evidenced in our simulation work. 34 In Fig. 3, it shows the localized partial electron density of the monoclinic and amorphous HfO 2 after they are negatively charged (À1), respectively.…”

“…Nevertheless, recent defect modeling work in SiO 2 reports that the hydrogen species related defect pairs in the SiO 2 have multiple characteristics under different stress situation. [32][33][34] This suggests that a similar degradation mechanism may exist in the HfO 2 oxide. Furthermore, simulation studies on amorphous HfO 2 networks report that disordered atomic structures in the dielectric (e.g., stretched Hf-O-Hf bond) could be an inherent relatively deep polarons.…”