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Representative atomic configurations of GeO structures: (a) the negatively charged threefold coordinated Ge atom (large gray balls), (b) the charge neutral twofold coordinated Ge atom, and (c) the positively charged threefold coordinated O atom (medium-size red balls). The electronic structure is illustrated through the centers of maximally localized Wannier functions (small black balls).
Electronic density of states (DOS) of the GeO model generated by ab initio molecular dynamics (GeO MD, dashed), of the GeO model generated by bond switching Monte Carlo (GeO MC, dotted), and of a model of amorphous (solid). The alignment is achieved through the levels and the energy scale is referred to the top of the valence band of . The shaded area indicates the Ge band gap aligned through the experimental value of 4.5 eV for the valence band offset (Ref. 22). The valence and conduction band edges (VBE and CBE) of are indicated.
Calculated 0/−2 charge transition level corresponding to the trapping of electrons in the GeO structures generated by ab initio molecular dynamics. The band alignment with Ge and is taken from Fig. 2. The inset illustrates the wave function of the electron trapping state, corresponding to a Ge–Ge bond.
Various Ge–Ge bond formation mechanisms by which the GeO structure traps two electrons, involving (a) two twofold coordinated Ge atoms, (b) a twofold coordinated Ge atom and a Ge atom bonded to a threefold coordinated O atom, and (c) two Ge atoms bonded to threefold coordinated O atoms. The superscripts indicate the charge states. Upon the bond formation in (b), preserves its threefold or fourfold coordination. The lobes indicate either occupied (filled) or unoccupied (open) dangling bonds.
Properties of the GeO models generated by ab initio molecular dynamics (MD) and by bond switching Monte Carlo (MC), compared to a model of amorphous : the number of atoms , the density (in ), the average Ge–O bond length (in Å), the average O–Ge–O angle, and the band gap (in eV).
Percentage of -fold coordinated Ge and O atoms in the low-density and high-density GeO models generated by molecular dynamics. Cutoff radii of 2.8 and 2.2 Å were used for Ge–Ge and Ge–O bonds.
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