Dislocation Kink Motion in Silicon

Electronic Doping Controlled Migration of Dislocations in Polycrystalline 2D WS2

Migration of dislocations not only determines the durability of large-scale nanoelectronic and opto-electronic devices based on polycrystalline 2D transition-metal dichalcogenides (TMDCs), but also plays an important role in enhancing the performance of novel memristors. However, a fundamental question of the migration dependence on the electronic effects, which are inevitable in practical field-effect transistors based on 2D TMDCs, and its interplay with different dislocations, remains unexplored. Here, taking WS₂ as an example, first-principle calculations are used to show that the electronic contributions arising from defect states can greatly influence the migration barriers of dislocations. The barrier height can be reduced by as much as 50%, which is mainly attributed to the change in electronic occupation and the band energy of defect levels controlled by electronic chemical potential (Fermi level). The reduced barriers in turn lead to significantly enhanced migration, and thus the plasticity. Since defect levels from dislocations locate deep inside the bandgap, the doping-induced tuning of barrier height can be achieved at relatively low doping concentration through either chemical doping or electrode gating. The effective electromechanical coupling in 2D TMDCs can provide new opportunities in material engineering for various potential applications.

Finding mechanism of transitions in complex systems: formation and migration of dislocation kinks in a silicon crystal

We demonstrate how a saddle point search method can be used to study dislocation mobility in a covalent material-a non-trivial transition mechanism in a complex system. Repeated saddle point searches have been carried out by using the minimum mode following algorithm and dimer method in combination with several empirical potential functions for silicon in order to determine the mechanisms for the creation and migration of kinks on a non-dissociated screw dislocation in a silicon crystal. For the environment-dependent interatomic potential, three possible kink migration processes have been identified with activation energies of 0.17, 0.25, and 0.33 eV. The Lenosky potential gives a single, low energy migration mechanism with an activation energy of 0.07 eV, in good agreement with density functional theory results. The kink formation mechanism determined using this potential has an activation barrier of 1.2 eV. Calculations were also carried out with the Tersoff potential, Stillinger-Weber potential and Bolding-Andersen potential. The various potential functions give quite different results for the kink structure and the mechanism of transition.

Thermal nucleation of kink-antikink pairs in the presence of impurities: the case of a Remoissenet-Peyrard substrate potential

Thermal nucleation of kink-antikink pairs in a nonlinear Klein-Gordon (NKG) model with a Remoissenet-Peyrard (RP) substrate potential in the presence of impurities and coupled to an applied field is analyzed in the limits of moderate temperature and strong damping. Using the Kolmogorov method, the average velocity of particles of the lattice is calculated and its dependence on the intensity of impurities is discussed in connection with the deformability parameter or the shape of the RP substrate potential. Numerical values are carried out by making use of parameters of the hydrogen atom adsorbed in the tungsten and ruthenium substrates. We show that, for large values of the applied field, the presence of impurities in the system makes the nucleation process of kink-antikink pairs more favorable in the high-temperature regime while they contribute to make it less favorable in the low-temperature regime.

Migration processes of the 30 degrees partial dislocation in silicon

The migration processes of the 30 degrees partial dislocation in silicon have been investigated using first-principles total-energy calculations. We have presented for the first time a reliable determination of the formation and migration energies of kinks, which are consistent with experiments. The obtained results indicate that the 30 degrees partial dominates the dislocation dynamics in Si and suggest the dislocation glide picture based on the no-collision model. We suggest that the interpretation of experimental studies on the dislocation dynamics should be reexamined in light of these results.

Vacancy interaction with dislocations in silicon: the shuffle-glide competition

Competition between the two alternative positions (shuffle and glide 111 plane subsets) for the core of a 30 degrees partial dislocation in Si is examined. Using a combination of ab initio total energy calculations with finite temperature free-energy calculations based on an interatomic potential, we obtained free energies for the relevant vacancy-type core defects. Generally, the free energy of vacancy formation in the core of a 30 degrees glide partial dislocation is considerably lower (by more than 1 eV) than in the bulk. However, even at high temperatures, the predicted thermal concentration of the shuffle segments comprised of a row of vacancies in the core is low, placing the 30 degrees partial dislocation in the glide subset position.

Hydrogen interaction with dislocations in Si

An H plasma has a remarkable effect on dislocation mobility in silicon, reducing its activation energy to 1.2 eV. Applying density functional theory to the interactions of H and H2 with the core of the 90 degrees partial dislocation in Si, we have identified a path for motion involving kink formation and migration at hydrogenated core bonds which conforms exactly to the experimentally measured activation energy.