First principles study of oxygen vacancy defects in amorphous SiO2

Abstract

The oxygen vacancy defects of amorphous SiO2 (a-SiO2) in different charge states are investigated by the periodic density functional theory. Five types of the positively charged configurations are obtained including the dimer, forward-oriented, puckered 4×, 5× and back-projected unpuckered configurations. The energy, geometry structure, spin density, Bader charge and Fermi contact are concerned for these systems. These defects can be regarded as the potential microscopic structures for the corresponding centers including Eα′, Eγ′ and Eδ′ in the electron paramagnetic resonance (EPR) experiments. Then, the charge-state transitions of these defects are investigated by intentionally adding one electron to the positively charged systems. For the dimer, puckered 4× and back-projected unpuckered configurations, all of the corresponding neutral species maintain their initial types of geometry structures. For the forward-oriented configurations, the corresponding neutral species transform into the structures of the divalent Si atom. The puckered 5× configurations have the most abundant neutral species: some of them could maintain its style of the puckered 5× configurations, and some collapse to the neutral dimer or forward-oriented configurations. The dimer configurations have the lowest thermodynamic charge-state levels, and the puckered 4× configurations have the highest thermodynamic charge-state levels among the five types of configurations. This work is of benefit to identifying and controlling the oxygen defects in a-SiO2.

Theoretical investigation of vacancy related defects at 4H-SiC(000$\bar{1}$)/SiO$_2$ interface after wet oxidation

“…The formation energies for the dry and wet oxidations The difference in the chemical potential of O atom between the rich and poor conditions, , respectively. In addition, when an O atom is assumed to be taken from SiO 2 with an oxygen vacancy, the difference in the chemical potential from that of an oxygen molecule, r O − O , is larger than 5 eV, 34,35) which is further O-atom poor condition. Thus, the silicon and carbon vacancies are more easily generated by wet oxidation than by dry oxidation near the SiC/SiO 2 interface because the formation energy of the vacancies by wet oxidation is larger than that by the dry oxidation under the O-atom poor condition ( O ≈ p O ).…”

Band Edge Energy Tuning through Electronic Character Hybridization in Ternary Metal Vanadates

“…The formation energy of both charged and neutral defects depends on the chemical potential of the added/removed species . For ZnO, the absolute formation energy is 3.72 eV (0.08 eV/FU) for a neutral V O , 1.94–3.84 eV (0.12–0.24 eV/FU) for FeWO 4 , 2.02–4.9 eV (0.12–0.31 eV/FU) for MnWO 4 , 6.72 eV (0.09 eV/FU) for SiO 2 , and 5.2–6.6 eV (0.08–0.83 eV/FU) for TiO 2 …”

Mechanisms and Models for the Suppressed Defect Dynamics in SiO2–Si Structures under High‐To‐Low Switched Dose Rate Irradiations

“…The rate constants of these two processes can be denoted as k h δ and k e δ , respectively. As indicated by Step 3, E 0 γ centers are generated in the SiO 2 region because holes migrating on relatively shallow V Oδ [20][21][22] are captured by much deeper V Oγ [3,14,18,[23][24][25] V…”

“…The rate constants of these two processes can be denoted as and , respectively. As indicated by Step 3, centers are generated in the SiO 2 region because holes migrating on relatively shallow [ 20–22 ] are captured by much deeper [ 3,14,18,23–25 ] This process is limited by the dispersive migration of holes in disordered SiO 2 . [ 20–22 ] Thus, the mobility of holes is a power‐law decay function of the irradiation time, [ 26,27 ] , where is an attempt frequency and a dispersion parameter, and the generation of centers is decelerated with a time‐decaying rate constant of , where is an estimated critical length similar to the concept of capture cross‐section.…”