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Schematics of the atomic configurations studied to model doping effects in TiO2 ReRAM. (a) Dopant and oxygen vacancy created in the 3 × 3 × 4 rutile TiO2 supercell; (b) dopant in the  di-vacancy filament (viewed from ).
Electron DOS calculated for the TiO2 supercells with the 9 kinds of dopants, and (a) without oxygen vacancy, or (b) with one vacancy next to the dopant. (b) shows both the total DOS and projected DOS on the dopant. The undoped case (Ti) is plotted as a reference. The Fermi levels of each system are indicated by red dashed lines.
Calculated electron bandstructures of (a) the oxygen vacancy filament without dopant; and the filament with (b) Hf, (c) V, (d) Ni, (e) Al, (f) Sr as substitutional dopants. The defect states in the bandgap are depicted by colored lines, and the conduction/valence bands are represented by grey lines. The red squares outline the filament direction (Γ-Z) in the bandstructure.
(a) Formation energies of single oxygen vacancy next to different types of dopants, calculated by DFT. (b) Average formation energies of oxygen vacancies in the filament doped with the metal dopants. Energy trends identical to the single vacancy case are observed.
Valence electron configurations and most common oxidization states of the dopants.
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