First principle calculations of iron and iron-boron transition levels in Si1−xGex alloy
This paper investigates, using first principle calculations, the charge transition levels Fe0/+ and FeB0/+, and the FeB binding energy in Si1−xGex alloy with composition x = 3 − 25%. The alloys were generated using an efficient code for the stochastic generation of special quasirandom structures. We found that the separation between Fe0/+ and FeB0/+ donor levels was ~0.24 eV (experimental value =0.28 eV) and was independent on x, in an agreement with the experiment. The pattern of the variation of the levels and band gap energies with x agreed very well with the experiment especially for x< 25 %. The formation of FeB-pairs was found to be favorable over individual Fe formation with average binding energy ~0.2 eV, agreeing with the first-principle calculation report using finite supercell size. In particular, the reliability of our method to reproduce the experimental results associated with the composition controlled FeB donor levels has successfully been demonstrated in the industrially interesting SiGe alloy material.
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