Path-integral Monte Carlo simulation of hydrogen in crystalline silicon

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Abstract
Isolated hydrogen and deuterium in crystalline silicon have been studied by the path-integral Monte Carlo method. Interactions between Si atoms were modeled by the Stillinger-Weber potential, and the Si-H interaction was parametrized by following the results of earlier pseudopotential-density-functional calculations for this system. Finite-temperature properties of these point defects are analyzed in the range from 50 to 600 K. Hydrogen and deuterium are found to be stable at the bond-center (B) site. Average values of the kinetic 〈K〉 and potential 〈V〉 energy of the defect are compared with those expected for the impurity within a harmonic approximation. At low temperatures, 〈K〉 is larger than 〈V〉, as a consequence of the strong anharmonicity of the potential surface for the impurity around the B site. The density distribution of the impurity at the B site displays axial symmetry around the Si-B-Si axis. The width of the density distribution along the bond direction is roughly one-half of that found for directions perpendicular to the symmetry axis.