Fast diffusion mechanism of silicon tri-interstitial defects

Abstract

Molecular dynamics combined with the nudged elastic band method reveals the microscopic self-diffusion process of compact silicon tri-interstitials. Tight-binding molecular dynamics paired with ab initio density functional calculations speed the identification of diffusion mechanisms. The diffusion pathway can be visualized as a five defect-atom object both translating and rotating in a screwlike motion along ͗111͘ directions. The density functional theory yields a diffusion constant of 4 ϫ 10 −5 exp͑−0.49 eV/ k B T͒ cm 2 / s. The low diffusion barrier of the compact tri-interstitial may be important in the growth of ion-implantation-induced extended interstitial defects.

Simulation of Single-Particle Displacement Damage in Silicon—Part III: First Principle Characterization of Defect Properties

“…All the other configurations have a much higher energy or correspond to the diinterstitial surrounded by another interstitial. The MEP for the diffusion of the tri-interstitial from its ground state 3V tetra to a neighbor 3V tetra needs the crossing of a 0.45 eV barrier coherent with previous work (0.49eV [22]) [21], whereas this barrier is 2.59 eV for the diffusion from a 3V block configuration to a 3V block configuration. For this reason, during annealing all the 3V tetra configurations diffuse, whereas the 3V block does not.…”

Diffusion mechanisms for silicon di-interstitials

“…Figure 2 demonstrates the similarity between the structure of the di-interstitial I 2 a and the compact tri-interstitial I 3 b . 15 The removal of one of the four interstitial atoms that form the tetrahedral defect I 3 b results in a structure that relaxes to I 2 a . Therefore, the tri-interstitial diffusion path 15 provides a possible pathway for the ground state di-interstitial I 2 a diffusion.…”

“…15 The removal of one of the four interstitial atoms that form the tetrahedral defect I 3 b results in a structure that relaxes to I 2 a . Therefore, the tri-interstitial diffusion path 15 provides a possible pathway for the ground state di-interstitial I 2 a diffusion. We remove one of the three atoms of I 3 b , that is rotating and translating during the diffusion, from the initial and final state of the I 3 b diffusion-path ͑see Fig.…”

“…The diffusion mechanism of the compact tri-interstitial 15 inspires an initial path for the diffusion mechanism of the I 2 a diinterstitials. Nudged-elastic band ͑NEB͒ calculations 16,17 using density functional methods [18][19][20] refine the transition path and determine the diffusion barriers of the path connecting the three lowest energy di-interstitial structures found in previous tight-binding molecular dynamics simulations.…”

“…The calculations are performed with the Vienna AB-INITIO Simulation Package ͑VASP͒. 18,19 Details of the methods 22 are described in our previous work 15 on the diffusion mechanism of tri-interstitial defects in silicon.…”