The structural and dynamic properties of H and D in B-doped material were studied, as a function of temperatures ranging from 30 to 400K, by using the path-integral Monte Carlo method. The Si-Si and Si-B interactions were modelled by using Stillinger-Weber type potentials, and the Si-H and B-H interactions were parametrized on the basis of earlier pseudopotential density-functional calculations for this system. Impurity energy, nucleus delocalization, and lattice relaxation were analyzed, with the latter being mass-dependent. The reorientation rate of the complex was obtained from quantum transition-state theory. A break in the slope of the Arrhenius plot for the jump rate of H was found at about 60K. This indicated a cross-over, from thermally activated quasi-classical motion over a barrier to thermally assisted quantum tunnelling, which was in good agreement with previous experimental results. In the case of D, this deviation from the Arrhenius law was found at about 35K. Both the impurity and the host nuclei were treated quantum mechanically, and it was shown that the defect complex undergoing quantum tunnelling consisted of H, B and the nearest Si atoms.

J.C.Noya, C.P.Herrero, R.Ramírez: Physical Review B, 1997, 56[23], 15139-50