Si isotopic structure of the infrared absorption of the fully hydrogenated vacancy in silicon

Abstract

An infrared absorption spectrum consisting in three lines observed around 2223 cm(-1) at liquid helium temperature characterizes a defect common in silicon crystals containing hydrogen. Several investigations of this spectrum have converged towards its assignment to a fully hydrogenated lattice vacancy defect V(Si-H)4. However, the fact that the ratios of the intensities of the three lines have been reported to be proportional to the natural abundances of the three silicon isotopes suggests that only one Si atom is involved in the defect, apparently contradicting the above assignment. In this paper, the spectroscopic investigation of this defect is revisited and the Si-related isotopic structures of V(Si-H)4 and V(Si-D)4 defects are modeled. It is shown that the near proportionalities observed between the intensities of these lines and the abundances of the Si isotopes are fortuitous. Our analysis of the isotope dependence of the 2223 cm(-1) line finds the V(Si-H)4 model to be correct and that the model of a single interstitial Si atom complexed with H can be rejected. The investigation is extended to the analysis of tetra-hydrogenated vacancy trapped by a carbon atom.