Universidad de Valladolid

Universidad de Valladolid

Energetic characterization

Energetic characterization of defects is very important since energies determine defect dynamics. Usually it is not easy to obtain individual defect energetics with experimental techniques. In turn, atomistic simulations can provide such kind of detailed information. For example, statical calculations using ab initio and tight-binding techniques can be employed to extract defect formation energies and small cluster binding energies. Classical molecular dynamics can be used to characterize bigger defects, and also to carry dynamical calculations in order to determine atomic diffusion paths and migration energies. The events and energies determined with these fundamental simulation techniques are then introduced in a kinetic Monte Carlo code able to reach macroscopic size and time scale

Using classical molecular dynamics techniques, we have shown that the point defect known as bond defect can be seen as the building block of the amorphous phase in semiconductors. We demonstrated that accumulation of bond defects leads to the progressive amorphization of the crystal lattice. We observed that the energy of this defect depends on the number of bond defect neighbors. The energetic characterization of the bond defect allowed us to develop an atomistic model for semiconductor amorphization suitable to kinetic Monte Carlo simulators, able to describe defect structures ranging from small amorphous zones to planar amorphous/crystal interfaces and full amorphous layers.

Defect Energetics
Arrhenius plot and activation energies for regrowth of different damage structures as obtained from classical molecular dynamics simulations.

Silicon self-interstitial configurations
Changes in the Si self-interstitial configuration and diffusion barriers during its diffusion (L. A. Marqués et al., Phys. Rev. B 71, 085204 (2005) - Molecular dynamics study of the configurational and energetic properties of the silicon self-interstitial).

We also used classical molecular dynamics simulation techniques to characterize the different configurations and energetics of the silicon self-interstitial. We found that this point defect may exist in four different configurations with diverse formation energies. These configurations are related to two different diffusion paths. We demonstrated that although the atomistic picture of the silicon self-interstitial is quite complex, its macroscopic behavior can be modeled by a simple description based on a unique interstitial species with effective formation and migration energies.


Structural characterization
Evaluation of the atomic structure of relevant defects and complexes
Energetic characterization
Modeling of the relevant energies that govern the stability and diffusion of defects
Electronic properties
Calculation of the electronic levels of defects to correlate with their macroscopic effects
Dynamical studies
Simulation of dynamics of defects based on fundamental properties