Defect-Enhanced Charge Transfer by Ion-Solid Interactions in SiC using Large-Scale Ab Initio Molecular Dynamics Simulations

Large-scale ab initio molecular dynamics simulations of ion-solid interactions in SiC reveal that significant charge transfer occurs between atoms, and defects can enhance charge transfer to surrounding atoms. The results demonstrate that charge transfer to and from recoiling atoms can alter the energy barriers and dynamics for stable defect formation. The present simulations illustrate in detail the dynamic processes for charged defect formation. The averaged values of displacement threshold energies along four main crystallographic directions are smaller than those determined by empirical potentials due to charge-transfer effects on recoil atoms.

Figure 1

(a) Three atomic configurations in a $(1\overline{1}0)$ plane showing defect generation at times of (A) 0.55, (B) 1.02, and (C) 2.0 ps, where the red and green spheres are Si and C atoms, respectively, and the Si PKA is represented by a black sphere and the Si vacancy by a white square. The gray spheres indicate two tetrahedral positions. (b) Charge-density difference contour plot for the final atomic configuration (C) in a $(1\overline{1}0)$ plane in units of $|e|/a_b{}^3$ ($a_b$-Bohr radius).

Figure 2

Variation of effective charge, gain ($+$), and loss ($-$) of electrons, for the C PKA along the $[\overline{1}\overline{1}\overline{1}]$ direction, where the orientations of the atomic configurations are the same as those in Fig. 1. The blue and yellow spheres represent the C PKA and secondary Si recoil atom, respectively, and the black diamonds indicate the charge differences obtained from the Bader charge analysis.

Figure 3

Variation of relative energy of the system as a function of time step, where there are two energy barriers corresponding to atomic configurations (B) and (D), respectively.

Figure 4

Charge-density contours (a), (b), and (c) in a $(1\overline{1}0)$ plane for atomic configurations (B), (D), and (E) in Fig. 2, respectively, where the vacancy and C interstitial are indicated.