MICROSCOPIC STRUCTURE AND REORIENTATION KINETICS OF B-H COMPLEXES IN SILICON

Structural and dynamical properties of hydrogen and deuterium in boron -doped silicon have been studied by the path-integral Monte Carlo meth od as a function of temperature in the range between 30 and 400 K. The Si-Si and Si-B interactions were modeled by Stillinger-Weber-type pot entials, and the SI-H and B-H interactions were parametrized by follow ing the results of earlier pseudopotential-density-functional calculat ions far this system. Impurity energy, nuclei delocalization, and latt ice relaxation an analyzed, the latter resulting to be mass dependent. The reorientation rate of the complex is obtained from quantum transi tion-state theory. A break in the slope of the Arrhenius plot for the jump rate of hydrogen is obtained at T similar to 60 K, indicating a c rossover from thermally activated quasiclassical motion over a barrier to thermally assisted quantum tunneling. in good agreement with previ ous experimental results. For deuterium, this deviation from an Arrhen ius law is found at T similar to 35 K. Both the impurity and the host nuclei are treated quantum mechanically, and it is shown that the defe ct complex undergoing quantum tunneling consists of hydrogen, boron, a nd the nearest silicon atoms.