A modified concerted exchange mechanism for antisite pair recombination in cubic and hexagonal silicon carbide

The antisite pair is one of the defect species which can be formed during ion beam processing of SiC. It consists of two neighboring atoms on “wrong” lattice sites, namely a Si atom on a C site and a C atom on a Si site. In general the experimental analysis of the different defect types formed during ion irradiation is difficult. Theoretical investigations on defect kinetics and defect evolution can be therefore very helpful to interpret the results of the annealing experiments with the irradiated samples. The antisite pair could not yet be identified unambiguously by experimental methods. Recently, the DI low temperature photoluminescence (PL) center has been correlated with the antisite pair [1]. In that theoretical work it is assumed that the antisite pair is stable up to a temperature of 2000 K. However, the thermal stability of the antisite pair has not yet been investigated. To our knowledge, there is only one work that is related to this topic [2]. Based on Pandey’s concerted exchange originally proposed for silicon [3], the antisite pair formation is studied by static potential energy calculations.

This work shows results of a systematic atomistic study on the thermal stabilty of the antisite pair and on the mechanisms of recombination in cubic (3C) and hexagonal (4H) SiC. At first the structure and energetics of the antisite pair is determined for T = 0 K. The results are compared with literature data which were obtained by the density-functional theory (DFT). The comparison shows that the interatomic potential used in the atomistic simulations yields reasonable data. The thermal stability of the antisite pair was investigated by molecular dynamics (MD) simulations at temperatures between 800 and 2500 K. Due to the statistical nature of the recombination process, it was necessary to perform several statistically independent simulations at every temperature. This was done by using different initial random numbers. The lifetime of the antisite pair was determined by different methods: (i) The evolution of the potential energy of the atoms which belong to the antisite pair and/or the potential energy of the atoms belonging to the defect and to the defect environment were analyzed. (ii) The time dependence of the recombination parameter was followed. (iii) The defect configuration was monitored visually. It is found that the thermal stability of the antisite pair is relatively low. It can be therefore not correlated with the DI low temperature PL center which is stable up to 2000 K. These results are confirmed by DFT-based MD simulations. The detailed study of the atomic rearrangements during the antisite pair recombination revealed a modified concerted exchange mechanism. Due to the different atomic sizes in SiC, this process is not identical with the concerted exchange proposed for Si [3] and considered by Rauls et al. [2] in order to explain the antisite pair formation in cubic SiC. Investigations of antisite pair recombination in hexagonal (4H) SiC yield results which are slightly different to those obtained for the cubic polytype.

[1] A. Gali, P. Deak, E. Rauls, N. T. Son, I. G. Ivanov, F. H. C. Carlsson, E. Janzen,
W. I. Choyke, Phys. Rev. B 67 (2003) 155203.
[2] E. Rauls, Z. Hajnal, A. Gali, P. Deak, T. Frauenheim, Materials Science Forum
353-356 (2001) 435.
[3] K. C. Pandey, Phys. Rev. Lett. 57 (1986) 2287.
[4] F. Cargnoni, C. Gatti, L. Colombo, Phys. Rev. B 57 (1998) 170.
[5] M. Tang, L. Colombo, J. Zhu, T. Diaz de la Rubia, Phys. Rev. B 55 (1997) 14279.