Computer Simulation of Energy Dependence of Primary Damage States in SiC
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Computer Simulation Of Energy Dependence Of Primary Damage States In SiC R. Devanathan*, F. Gao**, and W. J. Weber** * Department of Metallurgical Engineering, Indian Institute of Technology Madras, Chennai 600036, India ** Pacific Northwest National Laboratory, MS K8-93, P. O. Box 999, Richland, WA 99352, USA
ABSTRACT The primary damage state in 3C-SiC has been comprehensively studied by molecular dynamics using a modified Tersoff potential. The simulations examined damage produced by Si and C primary knock-on atoms (PKA) with energies from 0.25 to 30 keV. The study also generated statistics of defect production by simulating a number of PKAs at each energy. The defect production efficiency decreases with increasing PKA energy, as observed previously in metals. However, the cascade lifetime is very short (less than 1 ps), localized melting does not occur, the defect arrangements are highly dispersed, and the tendency for defects to form clusters is much less compared to the case of metals. Frenkel pairs on the C sublattice are more numerous than Si Frenkel pairs, and 10-20% of the displacements are in the form of anti-site defects.
INTRODUCTION Silicon carbide is a high temperature and radiation resistant semiconductor with potential applications in industries where direct process monitoring is required under adverse environments [1]. SiC-based composite materials are also promising candidates for structural applications in fission [2] and fusion [3] reactors. Both high-dose ion-implantation and neutron irradiation result in the accumulation of non-equilibrium concentrations of point defects. The microstructural changes brought about by these defects need to be understood in order to realize the full potential of SiC-based materials. Direct experimental observation of defect creation processes is not possible because the processes take place on small time (ps) and distance (nm) scales. Realistic molecular dynamics simulations performed in conjunction with experiments are needed to fill the gaps in the current knowledge of defect creation and evolution in SiC. Recently, molecular dynamics simulations using the Tersoff potential [4] have been employed to study displacement events and low-energy cascades in SiC [5-9]. The present study extends understanding of the primary damage state in SiC to higher energies and provides statistics of defect production in displacement cascades.
DETAILS OF THE SIMULATION Molecular dynamics simulations were performed at 300 K using a version of the MDCASK code [10]. The interatomic potential used was a combination of the Tersoff potential and a first principles repulsive potential and has been described previously [6]. Periodic boundary conditions were imposed along with a damping force at the boundaries to prevent energy leaving the simulation cell from re-entering it at the opposite face. The size of the cell varied from 8000 atoms for damage energies of 0.25 and 0.5 keV to 2 million atoms for 30 keV. The cascades with damage energy less than 1 keV were simulated using a desktop
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