Hydrogen in C-rich Si and the diffusion of vacancy-H complexes

The sites, gap levels, and migration barriers of interstitial H in Si are predicted. The hydrogenation of C-rich Si results in the formation of H ₂*(C) and C ₂H ₂, in contrast to FZ-Si where H ₂ molecules dominate. The fully saturated vacancy (VH ₄) also forms. This complex is normally stable up to 650 °C. However, in C-rich Si, VH ₄ anneals around 550 °C while the VH ₃HC complex appears. There, C replaces one of the four Si nearest-neighbors to the vacancy. This implies that VH ₄ begins to diffuse at 550 °C, and then traps at C _s. This in turn implies that all the VH _n complexes (n = 1, 2, 3, 4) are mobile at moderate temperatures. In this paper, we discuss the energetics of H in Si, summarize the key experimental and theoretical results about H interactions in C-rich Si, and discuss the migration paths and activation energies of the four VH _n complexes.