Anisotropic Displacement Threshold Energies in Silicon by Molecular Dynamics Simulations
- PDF / 309,392 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 99 Downloads / 232 Views
ANISOTROPIC DISPLACEMENT THRESHOLD ENERGIES IN SILICON BY MOLECULAR DYNAMICS SIMULATIONS*
LeAnn A. Miller,'
David K. Brice,l Anil K. Prinja, 2 and S. Thomas Picraux1
ISandia National Laboratories, Albuquerque. NM lniversity of Now Mexico, Department of Chemical and Nuclear Engineering, 2
Albuquerque, NM
Abstract A combination of molecular dynamics simulations and theoretical modeling was used to examine the orientation dependent threshold energies for displacement of silicon atoms from their lattice site due to energetic particle collisions. These results are important for a detailed understanding of both radiation effects in silicon devices and beam-enhanced stimulation of molecular beam epitaxial growth. The molecular dynamics code developed for this study, which employs a Tersoff interaction potential, as well as the theoretical model that incorporates the symmetry of the crystal are described. Bulk displacement threshold energies were determined by the molecular dynamics code for four directions through the open face in the . These values were then incorporated into the theoretical model for the average bulk displacement threshold energy. The average bulk displacement threshold energy was found to be 14.8 eV in 30° about and 11.1 eV in 20° about .
Introduction Models of radiation damage in crystalline materials typically assume a sharp energy threshold, Ed, for initiating atomic displacements from their ideal lattice sites (1]. The directional dependence of the displacement threshold energy is important in the development of a detailed understanding of both radiation effects in silicon devices [2] and beam-enhanced stimulation of molecular beam epitaxial growth [3]. To yield a better understanding of this phenomenon a combination of theoretical modeling and Molecular Dynamics (MD) simulations was used. This involved developing a MD code and a theoretical model of the displacement energy. Both of these tasks are discussed below as well as the application of the method to compare our results
with previous experimental measurements and modeling [2].
Theoretical Model
Experimental data for silicon was compared with several simple models for the bulk displacement threshold energy, Ed(8,0), in reference 2. The comparisons favored a model in which the average value of the bulk displacement threshold energy over a 30* cone of angles centered on , toward the open *This
work was performed et Sandie National Laboratories which is operated by the Department of Energy under
Contract Number DE-ACOA-76DPO0789.
Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research Society
172
face of the basic tetrahedron (see Figure 1), was 22 eV. The average value of Ed over a 20° cone of angles centered on was 26 eV, while displacements were not allowed outside these cones. We expand Ed(B,0) as a function of the polar angle, 0, and azimuthal angle, 0, about these two crystallographic directions in order to take advantage of crystal symmetry in evaluating the average value, , for comparison with these previous studies.
Data Loading...
