It was recalled that O diffused with an activation energy of some 2.53 to 2.56eV. In the case of hydrogenated samples, this activation energy decreased to some 1.6 to 2.0eV. Here, a microscopic mechanism for H-enhanced O diffusion in p-doped material was proposed. A path for the joint diffusion of O and H was deduced from an ab initio molecular dynamics simulation in which the O atom was kicked away from its equilibrium position with a given initial kinetic energy. After reaching a maximum potential energy of 1.46eV above the ground state, the system then relaxed to a metastable state in which a Si-Si bond was broken and the H atom saturated one of the dangling bonds. With an extra 0.16eV, the Si-H bond was broken and the system relaxed to an equivalent ground-state configuration. Therefore, the migration pathway involved an intriguing 2-step mechanism. This path represented an 0.54eV reduction in the static barrier when compared with the diffusion of isolated O; in excellent agreement with experiment. This mechanism therefore assumed that a H atom not only served to open a Si-Si bond to attack by O, but also helped to reduce the energy of an important intermediate state in the diffusion path.

R.B.Capaz, L.V.C.Assali, L.C.Kimerling, K.Cho, J.D.Joannopoulos: Physical Review B, 1999, 59[7], 4898-900

Table 191

Diffusivity of P in Si